@conference {JRN55350, title = {An extreme precipitation event, abrupt grass recovery, and soil processes in the Chihuahuan Desert}, booktitle = {Ecological Society of America (ESA)}, year = {2022}, month = {07/11/2022}, abstract = {Landscapes in the northern Chihuahuan Desert have been undergoing a gradual shift from perennial grassland to shrubland over the past century, driven primarily by the legacies of historical disturbance events and ongoing aridification. Nonetheless, extreme high rainfall periods can result in instances of remarkable grassland recovery, although they are highly patchy. In one area on the USDA-ARS Jornada Experimental Range, abrupt grass recovery occurred in an eroding Prosopis glandulosa shrubland state in response to a high rainfall period (2007-2009){\textemdash}an event that we did not imagine could happen. We are comparing ecosystem processes in this {\textquotedblleft}recovered savanna{\textquotedblright} to 1) patches of grassland that are in a relatively unaltered {\textquotedblleft}reference{\textquotedblright} state and 2) patches of shrubland state in which grass recovery did not occur. We asked a) is the recovered savanna similar to the reference grassland with respect to structure, composition, and vegetation-soil feedbacks and b) what led to spatial variation in grassland recovery? We compared vegetation and soil chemical and physical properties at twelve replicate study plots in each of the three states: recovered savanna, reference grassland, and shrubland. In addition, we are monitoring soil volumetric water content and aeolian sediment flux within each state. ~ We found that although the species composition of grasses differed strongly between reference grassland and recovered savanna, ecosystem functions measured were largely similar between these states but differed from shrubland states. Infiltration rate, soil aggregate stability, soil organic carbon, and soil C:N ratio were typically similar between reference grassland and recovered savanna but often far higher than in shrubland. Large bare gaps between plant canopies in the shrubland enabled far higher aeolian sediment fluxes than in the reference grassland and recovered savanna where bare gap connectivity was smaller. Static (edaphic) soil properties and volumetric water content in recovered savanna were intermediate between reference grassland and shrubland, suggesting that sites experiencing grass recovery may have been predisposed to grass establishment by virtue of their topoedaphic settings, yet were not resilient enough to avoid grass loss in the first place. The recovered savannas persist after a decade (including extreme dry years), provide ecosystem services comparable to the reference grasslands that originally occupied these sites, and are superior to the shrublands that they recently replaced. The question before us now is how to encourage more shrubland to savanna transitions.}, keywords = {abrupt grass recovery, Chihuahuan Desert, extreme precipitation event, soil, soil processes}, author = {Brandon T Bestelmeyer and Matthew Levi and Neeshia Macanowicz and Heather L. Throop and Nicholas Webb} } @article {JRN55413, title = {Simulated distribution of Eragrostis lehmanniana (Lehmann lovegrass): Soil{\textendash}climate interactions complicate predictions}, journal = {Ecosphere}, volume = {13}, year = {2022}, month = {3/7/2022}, pages = {e3974}, abstract = {The invasive perennial grass Eragrostis lehmanniana has expanded rapidly throughout the Sonoran Desert (SD) while remaining sparse and patchily distributed in the neighboring Chihuahuan Desert (CD). As temperatures and patterns in precipitation change, identifying the drivers limiting spread in the CD is needed. Our objectives were (1) to identify the climatic and edaphic factors limiting recruitment of E. lehmanniana throughout the CD and (2) to predict the edaphic and climatic locations in the CD where this species is expected to have higher probabilities of recruitment under future climatic conditions. Recruitment was simulated at 57 locations throughout the CD with a daily, multilayer soil water model (SOILWAT) that was parameterized and tested to develop recruitment parameters for E. lehmanniana using long-term data from research stations in the SD and CD. Logistic regression was used to predict recruitment across the CD using climate and soil factors to create a map of simulated recruitment under current and alternative climate scenarios. Simulated recruitment under current climate was low for most of the CD. However, localized areas with high probabilities (>0.8) occurred along the western transition between the CD and the SD, and in the southern extent of the CD. In general, the CD climate is too cool and dry for rapid and widespread invasion. However, increases to temperature and precipitation are likely to increase recruitment success. Interactions among soil, tempera-ture, and precipitation were important to increases in recruitment of E. lehmanniana and are expected to lead to heterogeneous increases in abundance as climate continues to change. This patchy increase in abundance will result in changes in its geographic distribution that will make predictions in the future challenging.}, keywords = {Chihuahuan Desert, climate change, Geographic distribution, numerical model, recruitment, seedling establishment, Special Feature: Dynamic Deserts}, doi = {10.1002/ecs2.3974}, url = {files/bibliography/22-022.pdf}, author = {N. Dylan Burruss and Debra.C.P. Peters and Haitao Huang and Jin Yao} } @proceedings {JRN55361, title = {Oryx (Oryx gazella gazella) presence patterns in a long term grazing study in the Chihuahuan Desert of New Mexico}, year = {2022}, month = {2/8/2022}, abstract = {A long term grazing study comparing the impact of grazing heritage (Raramuri Criollo) vs. commercial (Brangus) beef cattle on desert rangelands was initiated in 2020 at the NMSU Chihuahuan Desert Rangeland Research Center (CDRRC). South African oryx (Oryx gazella gazella) were introduced in the 1970s onto White Sands Missile Range, located ca. 20 miles east of the CDRRC, and oryx are frequently observed in our 5,000 ha study pastures. However, patterns of oryx presence in the grazing experiment pastures have not been determined. Hence, we sought to quantify oryx presence in our study pastures to help clarify: a) their potential impact on our experiment treatments; and b) cattle-, vegetation-, season- and ranch infrastructure- related factors associated with patterns of oryx presence in our experimental pastures. We obtained ca. 2,250 images from 40 trail cameras located in our four study pastures (10 cameras/pasture). Images were collected over a nine month phase repeated in two consecutive years, 2020 and 2021. Annually, images were collected during 3 periods: a) pre-grazing (Dec{\textendash}Feb), three months prior to placing cattle in the experiment area; b) grazing, when cattle grazed the experiment pastures (Mar{\textendash}May); and c) post-grazing, the three months after cattle were removed from pastures (Jun{\textendash}Aug). Grazing occurred in pastures only in 2020; no grazing occurred in 2021 because of severe drought conditions. These data will be compared with fecal pellet counts observed on permanent 100m transects at the camera locations to corroborate relative oryx presence. Additionally, vegetation cover data were collected at the permanent transects to determine potential relationships between oryx presence and plant cover. Our poster will report on oryx presence patterns across our study pastures with respect to cattle presence, vegetation, ranch infrastructure (distance to roads and drinkers), and season of the year. }, keywords = {Chihuahuan Desert, grazing study, long term, New Mexico, Oryx, Oryx gazella gazella, patterns, presence}, author = {M. Funk and Matthew M. McIntosh and Bender, L. and Andr{\'e}s F. Cibils and Andrew Cox and Fuentes-Soriano, S. and S. Spiegal and Richard E. Estell} } @conference {JRN55423, title = {Virtual fencing of nursing cattle grazing large pastures of Chihuahuan Desert rangelands}, booktitle = {Society for Range Management}, year = {2022}, abstract = {Virtual fencing (VF) is an emerging technology to control livestock dispersal. This technology includes collars that employ auditory-electric pulse cues to deter animals from trespassing into excluded zones. Our objective was to investigate VF application on extensive rangelands. VF-trained nursing Brangus cows were grazed in a 480 ha pasture at the New Mexico State University{\textquoteright}s Chihuahuan Desert Rangeland Research Center with the VF deactivated (control) or activated using three different polygon configurations. The VF-activated polygons excluded cattle from grazing either the East (209ha), West (200ha), or preferred Vegetation PV (80ha) within the pasture. Each pasture deployment lasted a week and the process was repeated on two groups of 11 and 18 cows, respectively. We analyzed 1) foraging behavior differences (control vs. VF-activated); 2) percentage of daily GPS locations within the excluded zones (control vs. VF-activated); and 3) number of auditory-electric pulses emitted during each VF-activated configuration (Excluded blocks East, West, or PV). The data were analyzed via an ANOVA to compare daily-derived variables. Cattle covered larger areas during control vs. VF-activated deployments (134.2 vs. 86.9ha P=0.04) with no differences in distance traveled nor cumulative activity index derived from the in-built motion sensors. When compared to the control, all VF-activated configurations significantly reduced the percentage of GPS positions within the excluded zone (East 52.27 vs. 0.67\%GPS P0<.01; West 18.49 vs. 0.49\%GPS P<0.01; PV 19.90 vs. 3.04\%GPS P<0.01; control vs. VF-activated respectively). Significantly (P<0.01) higher audio and electric pulses (2.09, 0.51 respectively) were emitted during the PV trials compared to East (1.12, 0.17) or West (1.12, 0.14) blocks. In conclusion, VF holds promise in controlling spatial exploration patterns of cattle in extensive rangelands. Polygon configuration requires further research to understand trade-offs between animal welfare and effective management.}, keywords = {cattle grazing, Chihuahuan Desert, large pastures, nursing, rangelands, virtual fencing}, author = {Nyamuryekung{\textquoteright}e, Shelemia and Andrew Cox and Perea, A. and Matthew M. McIntosh and Richard E. Estell and Andr{\'e}s F. Cibils and Holland, J. and Tony Waterhouse and G. Duff and M. Funk and Skye Aney and S. Spiegal and Brandon T Bestelmeyer and S. A. Utsumi} } @article {JRN55325, title = {Quadrat-based monitoring of desert grassland vegetation at the Jornada Experimental Range, New Mexico, 1915-2016}, year = {2021}, abstract = {The data set covers a 101-year period (1915{\textendash}2016) of quadrat-based plant sampling at the Jornada Experimental Range in southern New Mexico. At each sampling event, a pantograph was used to record the location and perimeter of living plants within permanent quadrats. Basal area was recorded for perennial grass species, canopy cover area was recorded for shrub species, and all other perennial species were recorded as point data. The data set includes 122 1 m by 1 m permanent quadrats, although not all quadrats were sampled in each year of the study and there is a gap in monitoring from 1980{\textendash}1995. These data provide a unique opportunity to investigate changes in the plant community over 100 years of variation in precipitation and other environmental conditions. We provide the following data and data formats: (1) the digitized maps in shapefile format; (2) data table containing coordinates (x,y) of perennial species within quadrats, including cover area for grasses and shrubs; (3) data table of counts of annual plant individuals per quadrat; (4) species list indicating growth form and habit of recorded species; (5) table of dates when each quadrat was sampled; (6) table of the pasture each quadrat was located within (note that pasture boundaries have changed over time); (7) table of depth to petrocalcic layer measurements taken at quadrat locations; (8) table of particle size analysis of soil samples taken at quadrat locations; (9) table of topographic characteristics of quadrat locations (e.g. concave or convex topography). Pantograph sampling is currently conducted at 5 year intervals by USDA-ARS staff, and new data will be added periodically to the EDI Data Portal Repository (see section V.E.2). This information is released under the Creative Commons license - Attribution - CC BY and the consumer of these data is required to cite it appropriately in any publication that results from its use.}, keywords = {arid grasslands, Chihuahuan Desert, long-term research, New Mexico, particle size analysis, plant community, plant populations, quadrat, rangeland, soil texture}, doi = {10.1002/ecy.3530}, url = {files/bibliography/21-041.pdf}, author = {Erica M. Christensen and D. K. James and A. L. Slaughter and Connie J. Maxwell and Peter B. Adler and Kris Havstad and Brandon T Bestelmeyer} } @article {JRN55328, title = {Foraging behavior and body temperature of heritage vs. commercial beef cows in relation to desert ambient heat}, journal = {Journal of Arid Environments}, volume = {193}, year = {2021}, month = {6/20/2021}, pages = {104565}, abstract = {We studied foraging patterns of Raramuri Criollo (heritage breed, {\textquotedblleft}RC{\textquotedblright}) and Angus x Hereford (commercial beef breed, {\textquotedblleft}AH{\textquotedblright}) cows in relation to ambient heat and body temperature during summer (2016 and 2017) and winter (2017 and 2018) in the Chihuahuan Desert. Cows of each breed grazed separately in two adjacent pastures (~1100 ha) in a crossover design for four weeks in each season/year. Animals were fitted with temperature loggers attached to blank CIDRs (Controlled Internal Drug Release device) devoid of hormones that recorded body temperature (BodyT), and GPS collars that recorded position and ambient temperature (CollarT). All sensor data were logged at 10 min intervals. A landscape thermal map (LandT) was developed from Landsat satellite imagery for habitat analysis using GPS locations chosen by individual collared cows, and air temperature (AirT) was recorded by a nearby weather station. Data were analyzed within four daytime segments: dawn (sunrise {\textendash} 9AM); pre-noon (9AM {\textendash} noon); post-noon (noon {\textendash} 3PM); and dusk (3PM {\textendash} sunset). ANOVA was used to determine whether BodyT, CollarT, LandT selection, or animal movement variables within each of the four daily segments differed (P < 0.05) for RC vs. AH cows. BodyT and CollarT increased as day progressed in both seasons. During summer, RC had lower BodyT and higher CollarT than AH (P < 0.05) during the hottest hours of the day. Increasing AirT throughout the day was associated with selection of cooler LandT in RC but not AH during summer. In winter, both breeds selected warmer landscape locations as the day progressed. Compared to AH, RC cows traveled farther, at higher velocities, and spent more time grazing and traveling and less time resting, with largest breed differences observed during the hottest hours of summer days. These results suggest that Raramuri Criollo cows exhibited higher thermotolerance than did AH. Elevated ambient summer temperatures in the Chihuahuan Desert appear to impose fewer constraints on heritage RC movement patterns compared to mainstream commercial AH cows.}, keywords = {Chihuahuan Desert, climate change, Raramuri Criollo, thermotolerance}, doi = {10.1016/j.jaridenv.2021.104565}, url = {files/bibliography/21-038.pdf}, author = {S. Nyamuryekung{\textquoteright}e and Andr{\'e}s F. Cibils and Richard E. Estell and Matthew M. McIntosh and D. VanLeeuwen and Caitriana Steele and Amy L. Gonzalez and S. Spiegal and Leonel Avenda{\~n}o Reyes and Felipe A. Rodr{\'\i}g Almeida and Martha Anderson} } @article {JRN55292, title = {Shrub encroachment, landscape restoration, and intraguild predation}, journal = {Journal of Arid Environments }, volume = {193}, year = {2021}, month = {July 10, 2021}, abstract = {Shrub encroachment into arid grasslands occurs globally with the potential to affect vertebrates and their interactions. In the Chihuahuan Desert of southern New Mexico, shrub encroachment has prompted intensive efforts by land management agencies to remove shrubs and restore historical grassland habitats. We asked if restoration actions involving shrub removal affected dynamics of intraguild predation (IGP) including an IGP predator (coyote, Canis latrans), an IGP prey (kit fox, Vulpes macrotis), plus their shared lagomorph prey. We used camera traps on 14 sites with paired treated and untreated areas to examine spatial and temporal niche partitioning of coyotes and kit foxes. Shrub removal did not produce straightforward effects on abundances of coyotes, kit foxes, or their prey resources. Instead, abundances of kit foxes were constrained when coyote abundance reached a threshold. Below this threshold, kit foxes were more common on areas with low shrub cover, possibly due to lack of hiding cover for lagomorph prey that increased their predation risk. Our system included two alternative states: IGP predator dominated and coexistence of IGP predator and prey. Coexistence may have been facilitated by temporal niche partitioning as diel activity patterns differed for coyotes and kit foxes. Future research on intraguild predation should integrate spatial and temporal niches to understand species coexistence including on dynamic landscapes undergoing restoration.}, keywords = {Canis latrans, Chihuahuan Desert, Diel activity, Intraguild predation, shrub encroachment, Valupes microtis}, doi = {10.1016/j.jaridenv.2021.104588}, url = {files/bibliography/21-026.pdf}, author = {Robert L. Schooley and Brandon T Bestelmeyer and John M. Coffman and Casey Wagnon} } @article {JRN55274, title = {Competition suppresses shrubs during early, but not late, stages of arid grassland{\textendash}shrubland state transition}, journal = {Functional Ecology}, volume = {33}, year = {2019}, month = {3/7/2019}, pages = {1480{\textendash}1490}, abstract = {1. Transitions from grass to woody plant dominance, widely reported in arid systems, are typically attributed to changes in disturbance regimes in combination with abiotic feedbacks, whereas biotic mechanisms such as competition and facilitation are often overlooked. Yet, research in semi-arid and subhumid savannas indicates that biotic interactions are important drivers in systems at risk for state transition. We sought to bridge this divide by experimentally manipulating grass-on-shrub and shrub-on-shrub interactions in early and late stages of grassland{\textendash}shrubland state transition, respectively, and to assess the extent to which these interactions might influence arid land state transition dynamics. 2. Target Prosopis glandulosa shrubs had surrounding grasses or conspecific neighbours left intact or killed with foliar herbicide, and metrics of plant performance were monitored over multiple years for shrubs with and without grass or shrub neighbours. 3. Productivity of small shrubs was enhanced by grass removal in years with above average precipitation, a result not evident in larger shrubs or during dry years. Proxy evidence based on nearest neighbour metrics suggested shrub{\textendash}shrub competition was at play, but our experimental manipulations revealed no such influence. 4. Competition from grasses appears to attenuate the rate at which shrubs achieve the size necessary to modify the physical environment in self-reinforcing ways, but only during the early stages of shrub encroachment. Our results further suggest that at late stages of grassland-to-shrubland state transitions, shrub{\textendash}shrub competition will not slow the rate of shrub expansion, and suggest that maximum shrub cover is regulated by something other than density-dependent mechanisms. We conclude that grass effects on shrubs should be included in assessments of desert grassland state transition probabilities and rates, and that desertification models in arid ecosystems that traditionally focus on disturbance and abiotic feedbacks should be broadened to incorporate spatial and temporal variations in competitive effects.}, keywords = {Chihuahuan Desert, competition, grassland, shrubland, state transition, woody plant encroachment}, doi = {10.1111/1365-2435.13336}, url = {files/bibliography/19-029.pdf}, author = {Nathan Pierce and Steven R. Archer and Brandon T Bestelmeyer} } @article {JRN55134, title = {Grass-Shrub competition in arid lands: An overlooked driver in grassland-shrubland state transition?}, journal = {Ecosystems}, volume = {22}, year = {2019}, month = {04/2019}, pages = {619-628}, chapter = {619}, abstract = {

Traditional models of state transition in arid lands emphasize changes in disturbance regimes and abiotic feedbacks that promote the degradation of grassland into shrubland, while biotic interactions like competition and facilitation are often overlooked. Here, we conducted an experiment to determine whether shrubs have a positive, neutral, or negative effect on grasses, and if these interactions may play a role in grassland-shrubland state transition. Prosopis glandulosa shrub neighbors within 5 m of Bouteloua eriopoda grass patches were left intact (controls) or killed with foliar herbicide, and metrics of grass performance were evaluated over 5 years. We saw no evidence of shrub facilitation of grasses. Instead, grass ANPP responded positively to shrub removal in all years, but more so in years with above-average rainfall. Grass allocation to vegetative reproduction and grass patch size also increased when shrub neighbors were removed. These results demonstrate that biotic interference by shrubs upon grasses reinforce and magnify grazing- and drought-induced abiotic feedbacks during grassland{\textendash}shrubland transitions. Shrub effects on grass should therefore be considered a key process in desert grassland state transitions.

}, keywords = {Bouteloua eriopoda, Chihuahuan Desert, competition, grassland, prosopis glandulosa, Scrublands, state transition, woody plant encroachment}, doi = {doi.org/10.1007/s10021-018-0290-9}, url = {files/bibliography/19-016.pdf}, author = {Nathan Pierce and Steven R. Archer and Brandon T Bestelmeyer and D. K. James} } @article {JRN54924, title = {Synchronous species responses reveal phenological guilds: implications for management}, journal = {Ecosphere}, volume = {9}, year = {2018}, month = {09/2018}, pages = {1-23}, chapter = {1}, abstract = {

Phenological studies are critical for understanding the ability of terrestrial ecosystems to respond to changes in climate. Monitoring seasonal transitions at the species or community level across large areas is challenging and expensive. One approach for lowering costs is to identify phenological guilds{\textemdash}groups of species that exhibit similar timing of seasonal transitions{\textemdash}and limit monitoring to a smaller number of species within a guild. In this study, we evaluated 23 consecutive years of monthly observations of individual species at 15 long-term study sites at the Jornada Basin USDA-Long-Term Ecological Research site to identify patterns in the onset of three phenophases{\textemdash}leaf-out, flower, and fruit{\textemdash}of 16 widely occurring species in the arid southwestern United States and to investigate the existence of phenological guilds. We conducted univariate analyses of distributions in the timing of leaf, flower, and fruit production across time and space and multivariate cluster analysis of the time series to identify coherent groups of species{\textendash}site instances that exhibit coherence in timing of phenophase onsets (i.e., guilds). The six species of C3 shrubs demonstrated greater consistency in timing of all phenophases relative to C4 grasses. Further, we found that in all species, leaf-out occurred prior to the onset of the summer monsoon rains. Cluster analysis revealed six groups of species{\textendash}site observations demonstrating high within-year concordance in timing of leaf-out and first fruit across variable site conditions and rainfall years. The six groups for timing of first fruit differed from those for first leaf in that they exhibited greater multi-species membership and within-year variability in timing. We propose that use of phenological guilds can improve the efficiency of ecosystem monitoring, predictive models of ecosystem cues driving phenological events, and land management outcomes.

}, keywords = {Chihuahuan Desert, drylands, first fruit, first leaf, long-term ecological research, pattern recognition, phenological functional group, plant phenology, Special Feature: Dynamic Deserts, start of season}, doi = {doi.org/10.1002/ecs2.2395}, url = {files/bibliography/18-017.pdf}, author = {Dawn M. Browning and Theresa Crimmins and D. K. James and S. Spiegal and Matthew Levi and John P. Anderson and Debra C. Peters} } @article {JRN54904, title = {Soil water dynamics at 15 locations distributed across a desert landscape: insights from a 27-yr dataset}, journal = {Ecosphere}, volume = {9}, year = {2018}, month = {07/2018}, pages = {36 pp}, abstract = {

Desert ecosystems are primarily limited by water availability. Within a climatic regime, topography, soil characteristics, and vegetation are expected to determine how the combined effects of precipitation, temperature, and evaporative demand of the atmosphere shape the spatial and temporal patterns of water within the soil profile and across a landscape. To forecast how desert landscapes may respond to future climatic conditions, it is imperative to improve our understanding of these ecohydrologic processes. Here, we report on 27 yr of monthly soil volumetric water content (VWC) measurements and associated soils data from a site in the northern Chihuahuan Desert of North America. The dataset includes VWC and soil properties measured to 3 m in depth across 15 locations that encompass a range of Chihuahuan Desert vegetation types. We use this unique dataset (1) to generate insights into general temporal and depth patterns in VWC, (2) to analyze how VWC corresponds to measures of climatic conditions, and (3) to qualitatively evaluate the relative importance of soils, topographic setting, and vegetation type in mediating temporal patterns in VWC. Analyses of this unique dataset emphasize the importance of soil and topographic setting in determining depth and temporal patterns in VWC across time. Results emphasize the episodic nature of deep wetting events in our study system{\textemdash}essentially limited to three large events over the 27-yr record driven primarily by wetter than normal winters. Comparison of soil water dynamics between mesquite shrub coppice dunes and interspace soils suggests the {\textquotedblleft}island of fertility{\textquotedblright} concept does not extend to soil water. Median VWC was strongly coupled to climatic conditions over surprisingly long windows at most locations (6{\textendash}18 months), suggesting that soil water at depth is decoupled from short climatic pulses. However, VWC dynamics and VWC{\textendash}climate relationships varied among locations, depths, and seasons, with unexpected similarities in ecohydrologic dynamics observed among very different vegetation types (e.g., an eroded creosote shrubland and a playa grassland). These results further underscore the importance of ecohydrological investigations in these ecosystems, given forecasts for a warmer and more variable climate in deserts globally.

}, keywords = {Chihuahuan Desert, coppice dunes, critical zone, deep recharge, desertification, ecohydrology, grassland, landscape context, neutron moisture meter, shrubland, soil water, Special Feature: Dynamic Deserts, vadose zone}, doi = {e02335. 10.1002/ecs2.2335}, url = {files/bibliography/18-013.pdf}, author = {Danielle Duni and Matthew D. Petrie and Debra C. Peters and John P. Anderson and K. Crossland and Jeffrey E. Herrick} } @article {JRN54901, title = {Shrub encroachment, productivity pulses, and core-transient dynamics of Chihuahuan Desert rodents}, journal = {Ecosphere}, volume = {9}, year = {2018}, month = {07/2018}, pages = {Article e02330}, abstract = {

Drylands worldwide are experiencing shrub encroachment into grasslands with potential consequences for biodiversity and ecosystem services. Climate change could increase the rate of shrub encroachment, amplify precipitation variability, and thus alter bottom-up processes for animal communities. Desert rodents are important biodiversity elements of arid grasslands and shrublands that exert strong effects on soil, vegetation, and other animal species. We used long-term data from the Jornada Basin Long Term Ecological Research site in the Chihuahuan Desert of southern New Mexico to ask whether bottomup control of desert rodents changes across shrub encroachment gradients. Our design included spatial blocks with replicated ecological states representing transitions from black grama (Bouteloua eriopoda) to honey mesquite (Prosopis glandulosa). Grassland-to-shrubland transitions did not produce degraded ecosystems, on average, with reduced net primary production or decreased rodent biomass. However, more rodent biomass was supported on unencroached grasslands following droughts whose frequency and severity may increase in southwestern United States. Hence, the observed evenness in rodent biomass across ecological states should be sensitive to climate change. The best predictors of rodent biomass also differed markedly for two trophic groups. This outcome was explained by considering core-transient dynamics. Granivores were mostly core species that regularly occurred on sites and responded to lagged net primary production at local scales, whereas folivores included transient species (especially Sigmodon hispidus) that responded to lagged precipitation at broader scales via spillover dynamics. Bottom-up processes for desert rodents across shrub invasion gradients were understood by integrating lagged responses to productivity pulses with core-transient structuring of communities.

}, keywords = {bottom-up control, Chihuahuan Desert, net primary production, precipitation variability, prosopis glandulosa, rodent communities, shrub encroachment, Special Feature: Dynamic Deserts}, doi = {e02330. 10.1002/ecs2.2330}, url = {files/bibliography/18-009.pdf}, author = {Robert L. Schooley and Brandon T Bestelmeyer and A. Campanella} } @article {JRN54905, title = {On the sensitivity of hillslope runoff and channel transmission losses in arid piedmont slopes}, journal = {Water Resources Research}, volume = {54}, year = {2018}, pages = {4498-4518}, abstract = {

Channel transmission losses alter the streamflow response of arid and semiarid watersheds and promote focused groundwater recharge. This process has been primarily studied in dryland channels draining large areas that are displaced away from hillslope runoff generation. In contrast, small watersheds on arid piedmont slopes allow the investigation of interactive hillslope and channel processes that control the partitioning between surface and subsurface flows. In this study, we utilize high-resolution, long-term measurements of water balance components in an instrumented watershed of the Chihuahuan Desert to set up, parameterize, and test a process-based, distributed hydrologic model modified to account for channel losses. A transient method for capturing capillary effects in channels results in simulations with a reliable representation of the watershed energy balance, soil moisture dynamics, hillslope infiltration, channel transmission (or percolation) losses, and streamflow yield over the study period. The simulation also reproduces a conceptual model of hillslope infiltration-excess runoff generation linked to downstream channel percolation losses that depend on the rainfall event size. Model-derived thresholds were obtained for the amount of hillslope runoff (6 mm) and rainfall (12.5 mm) necessary for streamflow yield, such that 40\% of percolation occurs for small events that do not reach the outlet. Using a set of scenarios, we identify that hillslope infiltration controls the rainfall threshold necessary to initiate percolation, while channel infiltration affects the partitioning into percolation and streamflow yield. Thus, the connectivity along hillslope-channel pathways is deemed an essential control on the streamflow generation and groundwater recharge in arid regions with complex terrain.

}, keywords = {channel transmission losses, Chihuahuan Desert, groundwater recharge, hillslope infiltration, hydrologic model, hydrology, percolation losses, piedmont slopes, runoff, soil moisture dynamics, streamflow yield, water balance}, doi = {10.1029/2018WR022842}, url = {files/bibliography/JRN54905.pdf}, author = {A. P. Schreiner-McGraw and Enrique Vivoni} } @article {JRN54812, title = {Percolation observations in an arid piedmont watershed and linkages to historical conditions in the Chihuahuan Desert}, journal = {Ecosphere}, volume = {8}, year = {2017}, pages = {Article e02000}, abstract = {

A critical hydrologic process in arid and semiarid regions is the interaction between ephemeral channels and groundwater aquifers. Generally, it has been found that ephemeral channels contribute to groundwater recharge when streamflow infiltrates into the sandy bottoms of channels. This process has traditionally been studied in channels that drain large areas (tens to hundreds of square kilometers). Since the water table in arid and semiarid regions is typically far from the surface, measured streamflow losses or percolation into the deep vadose zone is equated to groundwater recharge. In this study, we use a water balance approach to estimate deep percolation in a first-order, instrumented watershed (4.7 ha) on a piedmont slope of the Jornada Experimental Range (JER) in the Chihuahuan Desert. Results indicate that runoff generated within the piedmont slope contributes significantly to deep percolation. During the short-term 6-yr study period, we estimated 385 mm of total percolation, 62 mm/yr, or a ratio of percolation to rainfall of 0.26. Based on the instrument network, we identified that percolation occurs inside channel areas when these receive overland sheetflow from hillslopes. We observed less streamflow leaving the watershed as compared to percolation during the study period, leading to an outlet streamflow to rainfall ratio of 0.02. Using long-term data sets available from the JER, we estimate that over the last 100 yr, 48 mm/yr of percolation occurs at the study site, a ratio of percolation to rainfall of 0.19. We then scale this up to determine the contribution of similarly sized watersheds on the piedmont slopes of the JER. These observations highlight the importance of arid piedmont slopes for generating groundwater recharge, in particular during above-average rainfall periods.

}, keywords = {Chihuahuan Desert, dryland ecohydrology, groundwater recharge, long term ecological research, Special Feature: Dynamic Deserts, watershed instrumentation}, doi = {10.1002/ecs2.2000 }, url = {files/bibliography/JRN00659.pdf}, author = {A. P. Schreiner-McGraw and Enrique Vivoni} } @article {JRN54583, title = {Effects of exurban development on trophic interactions in a desert landscape}, year = {2016}, abstract = {

Context. Mechanisms of ecosystem change in urbanizing landscapes are poorly understood, especially in exurban areas featuring residential or commercial development set in a matrix of modified and natural vegetation. We asked how development altered trophic interactions and ecosystem processes in the matrix.
Objectives. We examined the effect of varying degrees of exurban development (housing density) on a trophic system that included an apex mammalian predator (coyote, Canis latrans), mammalian herbivores (lagomorphs and rodents), and herbaceous plants. We tested the hypothesis that plant recruitment would be negatively affected by exurban development due either to increases in herbivores associated with increased resource availability (a bottom{\textendash}up effect) or to a reduction in predators that avoid humans (a top{\textendash} down effect).
Methods. In Las Cruces, New Mexico, USA, four replicate sites were located in each of three urbanization levels: high density exurban, low density exurban, and wildland dominated by Chihuahuan Desert vegetation. Seedling trays measured herbivory rates, live trapping estimated abundance of pocket mice and kangaroo rats, and remotely-triggered wildlife cameras estimated the activity of lagomorphs and coyotes.
Results. Increased herbivory on seedlings and decreased herbaceous plant recruitment were observed in high density exurban areas. Overall rodent abundance, seed consumption rates, and activity of the lagomorph Lepus californicus did not vary with urbanization level. Activity by another lagomorph, Sylvilagus audubonii, and coyotes was highest in dense exurban areas, consistent with a bottom{\textendash}up effect.
Conclusions. Exurban development can have important indirect effects on trophic interactions occurring in adjacent, untransformed ecosystems. Similar to earlier studies, such effects in the Chihuahuan Desert may be mediated by bottom{\textendash}up processes associated with anthropogenic inputs.

}, keywords = {Chihuahuan Desert, coyote, lagomorph, plant recruitment, rodent, urbanization}, doi = {10.1007/s10980-016-0403-9}, url = {/files/bibliography/16-025.pdf}, author = {Kristen Davanon and Lindsey Howard and Karen Mabry and Robert L. Schooley and Brandon T Bestelmeyer} } @article {JRN54388, title = {Quantifying how short-term environmental variation leads to long-term demographic responses to climate change}, journal = {Journal of Ecology}, year = {2015}, pages = {1-12}, abstract = {

1. Climate change is expected to alter not only year-to-year variation in climate but also aspects of within-year variation, such as the length of the intervals between rainfall events and the duration of heat waves. Yet we still have a poor understanding of how intra-annual climate variability and individual weather events alter key vital rates (e.g. individual growth, reproduction and survival) that in part determine population dynamics.

2. Traditionally, ecologists have accounted for this variability across long time periods by attempting to correlate annual vital rates with measures of within-year variability (e.g. the coefficient of variation) to match the scale at which demographic data are collected. An alternative to this aggregate approach is to use within-season yet still relatively infrequent censuses in a probabilistic framework to determine the most likely way that vital rates respond to shorter-term variation in the environment, and how these short-term changes cumulatively lead to the observed yearly vital rates.

3. Here, I present an approach for inferring daily responses of vital rates to short-term weather variability, and apply it to understand how five species of summer annual plants in the Chihuahuan Desert will respond to climate change.

4. Vital rate models reveal that species differ in their responses to above- and below-average conditions, but generally fall into two life histories: (i) species that have fast growth on favourable days, but also experience higher mortality on less favourable days, and (ii) species that have slower growth in the same conditions but lower mortality. Results show that the expected rainfall changes in the Chihuahuan Desert (more late, cool season rainfall and less frequent, more intense rainfall events) could reduce growth and increase mortality of all summer annual plants.

5. Synthesis. My study shows that vital rates can change in response to short-term variability even when the total amount of rainfall and average temperature, common covariates in demographic models, remain constant. Accounting for changes in short-term environmental variation in climate change predictions will likely be important in systems with considerable environmental variation between censuses. The approach I present here can be widely applied to understand how short-term variability and individual weather events will alter organism responses to climate change.

}, keywords = {annual plants, Chihuahuan Desert, climate change, demography, intra-annual variability, missing data, plant{\textendash}climate interactions}, doi = {10.1111/1365-2745.12490}, author = {Shriver, Robert K.} } @article {JRN54151, title = {Scale-dependent feedbacks between patch size and plant reproduction in desert grassland}, journal = {Ecosystems}, volume = {18}, year = {2015}, month = {01/2015}, pages = {146-153}, chapter = {146}, abstract = {

Theoretical models suggest that scale-dependent feedbacks between plant reproductive success and plant patch size govern transitions from highly to sparsely vegetated states in drylands, yet there is scant empirical evidence for these mechanisms. Scale-dependent feedback models suggest that an optimal patch size exists for growth and reproduction of plants and that a threshold patch organization exists below which positive feedbacks between vegetation and resources can break down, leading to critical transitions. We examined the relationship between patch size and plant reproduction using an experiment in a Chihuahuan Desert grassland. We tested the hypothesis that reproductive effort and success of a dominant grass (Bouteloua eriopoda) would vary predictably with patch size. We found that focal plants in medium-sized patches featured higher rates of grass reproductive success than when plants occupied either large patch interiors or small patches. These patterns support the existence of scale-dependent feedbacks in Chihuahuan Desert grasslands and indicate an optimal patch size for reproductive effort and success in B. eriopoda. We discuss the implications of these results for detecting ecological thresholds in desert grasslands.

}, keywords = {Bouteloua eriopoda, Chihuahuan Desert, critical threshold, desertification, dryland, feedbacks, patch size, resilience, state transition}, doi = {10.1007/s10021-014-9818-9}, url = {/files/bibliography/15-008.pdf}, author = {L.N. Svejcar and Brandon T Bestelmeyer and Danielle Duni and D. K. James} } @article {JRN53950, title = {The landscape of fear: The missing link to understand top-down and bottom-up controls of prey abundance?}, journal = {Ecology}, volume = {5}, year = {2014}, month = {06/2014}, pages = {1141-1152}, chapter = {1141}, abstract = {

Identifying factors that may be responsible for affecting and possibly regulating the size of animal populations is a cornerstone in understanding population ecology.\  The main factors that are thought to influence population size are either resources (bottom-up), predation, (top-down), or interspecific competition (called here- parallel influences).\  However, studies of these effects have produced highly variable and often contradictory results regarding the relative strengths and influence of these factors. These varied results are often interpreted as indicating {\textquotedblleft}shifting control{\textquotedblright} among the three forces or existence of a complex, non-linear relationship among precipitation, resource availability, predation, and competition.\  We argue here that these interpretations suggest a {\textquotedblleft}missing link{\textquotedblright} in our understanding of predator-prey dynamics.\  We explore whether the landscape of fear model can clarify the inconsistencies and help us understand the roles, extent, and possible interactions of top-down, bottom-up, and parallel factors on prey population abundance.\  We propose various predictions derived from the landscape of fear model.\  For a single species, we suggest that as the makeup of the landscape of fear changes from relatively safe to relatively risky, bottom up impacts switch from comparatively strong to weak as top-down impacts go from weak to strong.\  For two or more species, interspecific competitive interactions produce various combinations of bottom-up, top-down, and parallel impacts depending on which competing species is superior and whether their landscapes of fear are shared or distinctive.\  We contend that these predications successfully explain many of the complex and contradictory results of current research.\  We end by testing some of these predictions based on long-term data for small mammals from the Chihuahuan Desert in the U.S. and M{\'e}xico.\  We conclude that the landscape of fear model does provide reasonable explanations for many of the results found and should be tested further and that this model has the possibility of being the {\textquotedblleft}missing link{\textquotedblright} in understanding bottom-up, top-down and parallel effects on population dynamics.

}, keywords = {bottom-up, Chihuahuan Desert, Dipodomys merriami, Durango, fox abundance, landscape of fear, Mapimi Biosphere Reserve, Merriami Kangaroo rat, parallel control effects, patch dynamics, predation risk, species conservation and management, top-down control, United States and Mexico}, doi = {10.1890/13-1083.1}, url = {/files/bibliography/14-012.pdf}, author = {John W. Laundre and Lucina Hern{\'a}ndez and Lopez Medina, Pete and A. Campanella and Lopez-Portilla, Jorge and Gonzales-Romero, Alberto and Grajales-Tam, Karina M and Burke, Anna M and Peg Gronemeyer and Dawn M. Browning} } @article {49841, title = {Changes in ecological stability across realistic biodiversity gradients depend on spatial scale}, journal = {Global Ecology and Biogeography}, volume = {22}, year = {2013}, pages = {19-28}, abstract = {

Aim: It is unclear how the stability of natural ecosystems and populations varies with biodiversity at spatial scales relevant to resource managers. This study evaluates whether theory and prior experiments adequately predict how stability varies with a measure of biodiversity, plant species richness, at multiple scales in naturally assembled ecosystems and assesses mechanisms through which biodiversity is proposed to affect stability.

Location: Chihuahuan desert. Historically, grasslands represented the dominant vegetation type in this landscape and shrubs were uncommon. Desertification has degraded many native grassland regions into one of several alternate states dominated by different shrub species and these regions differ in biodiversity.

Methods: Researchers at the Jornada long-term ecological research site have amassed 12 years of data on the primary productivity of individual plant species in 735 permanent 1-m2 plots distributed among 15 regions that were all historically grasslands. I used this information to describe the relationship between biodiversity and stability at the local (1 m2) and regional (3721 m2) scale and to evaluate mechanisms through which biodiversity is proposed to affect stability.

Results: At the local scale, ecosystem stability increased linearly with biodiversity while population stability tended to decline with biodiversity. At the regional scale, both ecosystem and population stability increased as a saturating function of biodiversity. Scale-dependent change in the biodiversity{\textendash}stability relationship can be explained by the spatial insurance hypothesis, asynchrony in the local productivity dynamics of the average species, and a change in species evenness with scale that weakens statistical averaging.

Main conclusions: Results from small-scale experimental studies may not directly translate to larger spatial scales but they appear to predict patterns in natural communities at small spatial scales. These results suggest that the maintenance of high biodiversity over a large spatial area is essential for maintaining ecosystem services and reducing the potential for further species extinctions.

}, keywords = {Chihuahuan Desert, ecosystem dynamics, grasslands, population dynamics, scale dependence, synchrony}, doi = {10.1111/j.1466-8238.2012.00779.x}, url = {files/bibliography/JRN00607.pdf}, author = {Chalcraft, David R.} } @article {49855, title = {Plant responses, climate pivot points, and trade-offs in water-limited ecosystems}, journal = {Ecosphere}, volume = {4}, year = {2013}, abstract = {

Plant species in dryland ecosystems are limited by water availability and may be vulnerable to increases in aridity. Methods are needed to monitor and assess the rate of change in plant abundance and composition in relation to climate, understand the potential for degradation in dryland ecosystems, and forecast future changes in plant species assemblages. I employ nearly a century of vegetation monitoring data from three North American deserts to demonstrate an approach to determine plant species responses to climate and critical points over a range of climatic conditions at which plant species shift from increases to decreases in abundance (climate pivot points). I assess these metrics from a site to regional scale and highlight how these indicators of plant performance can be modified by the physical and biotic environment. For example, shrubs were more responsive to drought and high temperatures on shallow soils with limited capacity to store water and fine-textured soils with slow percolation rates, whereas perennial grasses were more responsive to precipitation in sparse shrublands than in relatively dense grasslands and shrublands, where competition for water is likely more intense. The responses and associated climate pivot points of plant species aligned with their lifespan and structural characteristics, and the relationship between responses and climate pivot points provides evidence of the trade-off between the capacity of a plant species to increase in abundance when water is available and its drought resistance.

}, keywords = {arid, Chihuahuan Desert, climate change, Colorado Plateau, cross-site, desertification, early warning sign, long-term monitoring, plant canopy cover, Sonoran Desert}, doi = {10.1890/ES13-00132.1}, url = {files/bibliography/JRN00612.pdf}, author = {Seth M. Munson} } @article {49856, title = {Regional signatures of plant response to drought and elevated temperature across a desert ecosystem}, journal = {Ecology}, volume = {94}, year = {2013}, month = {09/2013}, pages = {2030-2041}, chapter = {2030}, abstract = {

The performance of many desert plant species in North America may decline with the warmer and drier conditions predicted by climate change models, thereby accelerating land degradation and reducing ecosystem productivity. We paired repeat measurements of plant canopy cover with climate at multiple sites across the Chihuahuan Desert over the last century to determine which plant species and functional types may be the most sensitive to climate change. We found that the dominant perennial grass, Bouteloua eriopoda, and species richness had nonlinear responses to summer precipitation, decreasing more in dry summers than increasing with wet summers. Dominant shrub species responded differently to the seasonality of precipitation and drought, but winter precipitation best explained changes in the cover of woody vegetation in upland grasslands and may contribute to woody-plant encroachment that is widespread throughout the southwestern United States and northern Mexico. Temperature explained additional variability of changes in cover of dominant and subdominant plant species. Using a novel empirically based approach we identified {\textquoteleft}{\textquoteleft}climate pivot points{\textquoteright}{\textquoteright} that were indicative of shifts from increasing to decreasing plant cover over a range of climatic conditions. Reductions in cover of annual and several perennial plant species, in addition to declines in species richness below the long-term summer precipitation mean across plant communities, indicate a decrease in the productivity for all but the most drought-tolerant perennial grasses and shrubs in the Chihuahuan Desert. Overall, our regional synthesis of long-term data provides a robust foundation for forecasting future shifts in the composition and structure of plant assemblages in the largest North American warm desert.

}, keywords = {Chihuahuan Desert, climate change, climate pivot point, desertification, forecasting plant community composition, land degradation, long-term vegetation dynamics, plant canopy cover, species richness}, doi = {10.1890/12-1586.1}, url = {/files/bibliography/13-027.pdf}, author = {Seth M. Munson and E. Muldavin and Jayne Belnap and Debra C. Peters and John P. Anderson and M. Hildegard Reiser and Gallo, Kirsten and Melgoza-Castillo, Alicia and Jeffrey E. Herrick and Christiansen, Tim A.} } @article {49862, title = {Precipitation legacies in desert grassland primary production occur through previous-year tiller density}, journal = {Ecology}, volume = {94}, year = {2013}, month = {04/2013}, pages = {435-443}, chapter = {435}, abstract = {In arid ecosystems, current-year precipitation often explains only a small proportion of annual aboveground net primary production (ANPP). We hypothesized that lags in the response of ecosystems to changes in water availability explain this low explanatory power, and that lags result from legacies from transitions from dry to wet years or the reverse. We explored five hypotheses regarding the magnitude of legacies, two possible mechanisms, and the differential effect of previous dry or wet years on the legacy magnitude. We used a three-year manipulative experiment with five levels of rainfall in the first two years (-80\% and -50\% reduced annual precipitation (PPT), ambient, +50\% and +80\% increased PPT), and reversed treatments in year 3. Legacies of previous two years, which were dry or wet, accounted for a large fraction (20\%) of interannual variability in production on year 3. Legacies in ANPP were similar in absolute value for both types of precipitation transitions, and their magnitude was a function of the difference between previous and current-year precipitation. Tiller density accounted for 40\% of legacy variability, while nitrogen and carryover water availability showed no effect. Understanding responses to changes in interannual precipitation will assist in assessing ecosystem responses to climate change-induced increases in precipitation variability.}, keywords = {aboveground net primary production, ANPP, black grama, Bouteloua eriopoda, Chihuahuan Desert, desert grasslands, mesquite, precipitation legacies, prosopis glandulosa, rainfall manipulation, tiller dynamics}, doi = {10.1890/12-1237.1}, url = {/files/bibliography/13-017.pdf}, author = {Lara Reichmann and O. E. Sala and Debra C. Peters} } @article {49861, title = {Water controls on nitrogen transformations and stocks in an arid ecosystem}, journal = {Ecosphere}, volume = {4}, year = {2013}, pages = {Article 11}, abstract = {

Following water, nitrogen (N) is the most frequent limiting factor to aboveground net primary production in arid ecosystems. Increased water availability can stimulate both plant nitrogen uptake and microbial nitrogen mineralization, but may also stimulate losses from the ecosystem. Here, we assess the effect of water availability on nitrogen stocks and transformations in an arid ecosystem. We conducted a field experiment with five levels of precipitation input (-80\%, -50\%, ambient, +50\%, +80\%) and two levels of N fertilization (ambient or 10 gm-2yr-1 NH4NO3) in a desert grassland of the Chihuahuan Desert. We measured in situ net N mineralization, plant N uptake, foliar N, N leaching under grass-rooting zone, and soil N availability during two years. Our results showed that increased water availability did not affect net N mineralization, but there was higher plant N uptake than with drought. Soil inorganic N pools were 2{\textendash}4 times lower with increased water availability compared to drought conditions. N leaching below grass-rooting zone was higher in dry than wet conditions because of higher available N. Increased water availability differentially affected N species significantly reducing the NO3:NH4 ratio. The accumulation of inorganic N during drought was the result of a decoupling between microbial and plant activity, and suggests that the cycling of N is more open in dry years than in wet years.

}, keywords = {arid ecosystems, Chihuahuan Desert, net N mineralization, nitrogen leaching, nitrogen-water interactions, soil inorganic N}, doi = {10.1890/ES12-00263.1}, url = {/files/bibliography/13-003.pdf}, author = {Lara Reichmann and O. E. Sala and Debra C. Peters} } @article {49876, title = {Hierarchial analysis of vegetation dynamics over 71 years: soil-rainfall interactions in a Chihuahuan Desert ecosystem}, journal = {Ecological Applications}, volume = {22}, year = {2012}, month = {04/2012}, pages = {909-926}, chapter = {909}, abstract = {

Proliferation of woody plants in grasslands and savannas is a persistent problem globally. This widely observed shift from grass to shrub dominance in rangelands worldwide has been heterogeneous in space and time largely due to cross-scale interactions among soils, climate, and land-use history. Our objective was to use a hierarchical framework to evaluate the relationship between spatial patterns in soil properties and long-term shrub dynamics in the northern Chihuahuan Desert of New Mexico, USA. To meet this objective, shrub patch dynamics from 1937 to 2008 were characterized at patch and landscape scales using historical imagery and a recent digital soils map. Effects of annual precipitation on patch dynamics on two soils revealed strong correlations between shrub growth on deep sandy soils and above-average rainfall years (r = 0.671, P = 0.034) and shrub colonization and below-average rainfall years on shallow sandy soils (r = 0.705, P = 0.023). Patch-level analysis of demographic patterns revealed significant differences between shrub patches on deep and shallow sandy soils during periods of above- and below-average rainfall. Both deep and shallow sandy soils exhibited low shrub cover in 1937 (1.0\% {\textpm} 2.3\% and 0.3\% {\textpm} 1.3\%, respectively [mean {\textpm} SD]) and were characterized by colonization or appearance of new patches until 1960. However, different demographic responses to the cessation of severe drought on the two soils and increased frequency of wet years after 1960 have resulted in very different endpoints. In 2008 a shrubland occupied the deep sandy soils with cover at 19.8\% {\textpm} 9.1\%, while a shrub-dominated grassland occurred on the shallow sandy soils with cover at 9.3\% {\textpm} 7.2\%. Present-day shrub vegetation constitutes a shifting mosaic marked by the coexistence of patches at different stages of development. Management implications of this long-term multi-scale assessment of vegetation dynamics support the notion that soil properties may constrain grassland remediation. Such efforts on sandy soils should be focused on sites characterized by near-surface water-holding capacity, as those lacking available water-holding capacity in the shallow root zone pose challenges to grass recovery and survival.

}, keywords = {aerial photography, Chihuahuan Desert, cross-scale linkages, ecological-state mapping, hierarchy theory, Jornada Basin LTER, New Mexico USA, object-based change detection, petrocalcic soil, prosopis glandulosa, shrub patch dynamics, shrub proliferation, soil depth}, doi = {10.1890/11-1193.1}, url = {/files/bibliography/12-026.pdf}, author = {Dawn M. Browning and Danielle Duni and Andrea S. Laliberte and A. Rango} } @article {JRN54212, title = {Long-term experimental loss of foundation species: consequences for dynamics at ecotones across heterogeneous landscapes}, journal = {Ecosphere}, volume = {3}, year = {2012}, month = {03/2012}, pages = {1-23}, chapter = {Article 27}, abstract = {

Biome transition zones where species co-exist near their geographic limits are expected to be among the most responsive to changes in climate that result in mortality of foundation species. Long-term (.13 years) patterns in dominance and cover of functional types were examined following the annual experimental removal of one of three foundation species at an arid-semiarid biome transition zone.\  Objectives were to identify key processes influencing these patterns, and to predict future landscape-scale dynamics following mortality of different foundation species. Aboveground biomass of dominant species was removed from 334 m plots. Cover by species on control and removal plots was estimated annually in communities with a single dominant species, and in ecotonal communities with two dominant species across two types of ecotones (semiarid grassland-arid grassland, arid grassland-arid shrubland).\  For most species and functional types, trends in cover through time were related to the remaining species assemblages rather than to variable climatic conditions. In ecotonal communities, resident co-dominant species increased to dominance following the loss of a foundation species with little change in community composition. In mono-dominated communities, dominant species loss resulted in a shift to species that are currently sub-dominants of the same functional type as the species that was removed. \ Subdominant perennial grass and shrub species increased rapidly following removals in most grassland locations.\  Annuals and perennial forbs had variable cover values through time that were not clearly related to pulses in precipitation and were not synchronized across locations. The most common response regardless of the identity of the foundation species removed or the community type was an increase in cover by subdominant grasses and by the arid grass species (Bouteloua eriopoda). The rate of increase by B. eriopoda depended on initial cover, and resulted from both vegetative growth and seedling recruitment from other locations. Seed dispersal and seedling recruitment from other locations were not found for the semiarid grass, Bouteloua gracilis or the arid shrub, Larrea tridentata. Because B. eriopoda is more susceptible to shrub invasion, drought, and livestock grazing than the other two foundation species, widespread loss of either of the other species and subsequent increase in B. eriopoda is expected to result in an increase in landscape scale vulnerability to these environmental drivers. The extent and magnitude of this change invulnerability will depend on the ability of B. eriopoda to respond based on the micro-environmental conditions of the site regardless of which species (B. gracilis, L. tridentata) is lost.

}, keywords = {arid, biome transitions, Chihuahuan Desert, dominant species, experimental removals, grasslands, mortality, semiarid, Shorrgrass Steppe, shrublands}, doi = {10.1890/ES11-00273.1}, url = {/files/bibliography/12-042.pdf}, author = {Debra C. Peters and Jin Yao} } @article {49901, title = {Landform influences on the resistance of grasslands to shrub encroachment, Northern Chihuahuan Desert, USA}, journal = {Journal of Maps}, year = {2012}, month = {11/2012}, pages = {1-7, iFirst Article}, abstract = {

In arid and semiarid regions, vegetative boundaries are often strikingly similar to landform boundaries. However, it is not well documented whether landforms exert an influence on the resistance of desert grassland to shrub encroachment. Dominant grassland communities have been displaced by woody shrubs over the last 150 years in the Jornada Basin, southern New Mexico. Digital vegetation maps from 1858, 1915{\textendash}1916, 1928{\textendash}1929, 1938, and 1998, in conjunction with a detailed landform map, were analyzed in a Geographical Information System. The generated time series maps and spatial data compiled from these datasets were used to quantify the extent and rate that grasslands were replaced by shrubs on eight contiguous landforms. From this assessment, we generated a resistance index that revealed desert grasslands were least resistant (most susceptible) to shrub expansion on sandy landforms and bajadas and most resistant to shrub invasion on ephemerally flooded playas. This study demonstrates that landforms both provide the broad-scale background for detailed mechanistic studies and affect the sensitivity of grasslands to shrub encroachment.\ 

}, keywords = {arid geomorphology, Chihuahuan Desert, desertification, grassland resistance, shrub encroachment}, doi = {10.1080/17445647.2012.727593}, url = {/files/bibliography/12-027.pdf}, author = {Rachal, David M. and Curtis H. Monger and Gregory S. Okin and Debra C. Peters} } @article {49916, title = {Spatial patterns of grasses and shrubs in an arid grassland environment}, journal = {Ecosphere}, volume = {2}, year = {2011}, month = {09/2011}, chapter = {Article 103}, abstract = {In the Chihuahuan Desert of Mexico and New Mexico, shrub invasion is a common problem, and once-abundant grassland ecosystems are being replaced by shrub-dominated habitat. The spatial arrangement of grasses and shrubs in these arid grasslands can provide better insight into community dynamics and can provide information on grass shrub interactions. To better understand the dynamics of the Chihuahuan Desert ecosystem and to provide information regarding the interactions between grasses and shrubs, we examined the spatial patterns of grasses and shrubs in remaining grass-dominated areas, interspersed with some shrubs. We developed 18, 10320 m vegetation distribution plots by mapping the location of all grasses and shrubs on each and repeating the measurements three years later. Spatial patterns were then assessed for each plot using a second-order spatial statistic, Ripley\’s K-function, as well as any observed changes in the spatial patterns over a three-year period. We observed clumped grass distributions, indicating a lack of competition among grasses; random shrub distributions; and even grass distribution with respect to shrub locations, indicating competition between grasses and shrubs. We also observed a tendency for grass distributions to become more even over time, and grasses to become less even with respect to shrub locations over time. These changes occurred during a period of greater than average rainfall, indicating that greater water availability may lead to increased competition among grasses and decreased competition between grasses and shrubs.}, keywords = {arid grasslands, Bouteloua eriopoda, Chihuahuan Desert, grass and shrub interactions, Jornada Experimental Range, prosopis glandulosa, Ripley{\textquoteright}s K-function, shrub expansion, spatial patterns, sporobolus spp.}, doi = {10.1890/ES11-00104.1}, url = {/files/bibliography/11-041.pdf}, author = {Lorelei Alvarez and Howard Epstein and Junran Li and Gregory S. Okin} } @article {49923, title = {Geomorphology of the Chihuahuan Desert based on potential dust emissions}, journal = {Journal of Maps}, year = {2011}, pages = {249-259}, abstract = {

The Chihuahuan Desert of central northern Mexico and southern Arizona, New Mexico and Texas, USA, is a regionally significant dust {\textquoteleft}hot-spot{\textquoteright} in North America. Typical of other such hot-spots, this desert consists of a mosaic of geomorphological settings, each of which has a varying propensity for dust emission. Recently, a classification system of dust emission potential based on surface geomorphic characteristics that establishes a common framework for describing the land surface has been proposed. The classification is readily applicable to different dust source regions and designed to facilitate comparison of the relative potential dust contributions and emissivity of varying geomorphological environments in such regions.

The map here (1:3,500,000) was compiled by applying the new classification to a base map of polygons from existing soil and landform maps that were produced by national government agencies. Within the study area, 11 of the 17 possible geomorphic classes were present, the most extensive being unarmoured, unincised high relief alluvial surfaces, which covered 43\% of the area.

As an example of how empirical dust source point data can be used with the classification, the satellite observed origins of dust plumes for 26 major wind erosion events from 2001 to 2009 were overlain on the map. Despite a total area of only 4\%, ephemeral lakes were the source of 48\% of the observed plumes. This map and the relationships derived from it provide the basis for developing equivalent maps in other dusty regions, and mark a step toward improving the representation and documentation of the strength of dust sources in numerical mineral aerosol models.

}, keywords = {Chihuahuan Desert, dust emissions, ephemeral lakes, geomorphology, playas}, doi = {10.4113/jom.2011.1178}, url = {files/bibliography/JRN00566.pdf}, author = {Matthew C. Baddock and Thomas E. Gill and Joanna E. Bullard and Acosta, Dominguez and Rivera Rivera, Nancy I.} } @article {49928, title = {Spatial perspectives in state-and-transition models: A missing link to land management?}, journal = {Journal of Applied Ecology}, volume = {48}, year = {2011}, month = {03/2011}, pages = {746-757}, chapter = {746}, abstract = {Conceptual models of alternative states and thresholds are based largely on observations of ecosystem processes at a few points in space. Because the distribution of alternative states in spatially-structured ecosystems is the result of variations in pattern-process interactions at different scales, we argue that data and models need to explicitly consider ecosystem processes in the context of the spatial pattern of drivers, spatial dependence in responses to drivers, and the spatial structure of feedbacks. Here, we review the literature on spatial patterns and processes in the context of state transitions (or regime shifts) and draw upon examples from semiarid ecosystems to illustrate these linkages. We suggest three spatial perspectives be used to expand conceptual state-and-transition (S\&T) models to landscape systems. First, S\&T models should represent how spatial patterns of natural and anthropogenic drivers interact to initiate transitions. This would account for often observed situations wherein contrasting states occur along gradients of disturbance intensity or in different management units. Second, spatial dependence in response to drivers and triggers should be represented. This would help account for observed differences in ecological resilience tied to inherent spatial variation in environmental variables (e.g., soil and landform attributes) that mediate driver effects and lead to variation in the likelihood of state transitions. Third, the nature of feedbacks, how they propagate over time and space, and how they are conditioned by patterns of spatial dependence and drivers should be represented. At fine scales, changes in the nature and intensity of feedbacks may be associated with predictable changes in patch structure (e.g., fragmentation or coalescence processes foreshadowing thresholds). At coarser scales, feedbacks may be associated with the spatial extent and arrangement of land cover states, broad-scale resource redistribution (e.g., wind/water erosion/deposition) or land surface/climate interactions. S\&T conceptual models with a spatial component would make use of readily-obtainable patch-scale data to predict how the likelihood of transitions might vary across landscapes and to forecast changes leading to degradation or recovery. Such predictions would be valuable in the design of monitoring schemes aimed at adjusting management to avert crossing degradation thresholds and to take advantage of environmental conditions required to restore desired states.}, keywords = {Chihuahuan Desert, contagion, Iceland, monitoring, patch dynamics, regime shift, southern Great Plains, spatial dependence, thresholds}, doi = {doi: 10.1111/j.1365-2664.2011.01982.x}, url = {/files/bibliography/11-007.pdf}, author = {Brandon T Bestelmeyer and D. Goolsby and Steven R. Archer} } @article {49945, title = {The association of land cover with aeolian sediment production at Jornada Basin, New Mexico, USA}, journal = {Aeolian Research}, volume = {3}, year = {2011}, pages = {55-66}, abstract = {

We investigated amounts and particle size distributions (PSDs) of aeolian sediments collected at five heights in five ecosystem types at the Jornada Basin, Chihuahuan Desert, New Mexico, USA. Particle size distributions, mass fluxes, and percent of dust-sized (650 lm) mass flux were determined for all heights and all ecosystem types. Differences between sites were determined using ANOVA followed by Tukey{\textendash}Kramer post hoc tests to find groupings. For creosote shrublands, grasslands, and two tarbush-dominated alluvial flats, samples collected at 5, 10, and 20 cm had \>80\% sand-sized (\>50 lm) particles, while one playa and tarbush site yielded ~45\% dust-sized particles at 5 and 10 cm. The transition from saltation to suspension was ~20 cm for most sites. Two mesquite dune sites and an anthropogenically devegetated site, all with high overall mass fluxes, shifted to suspension at ~50 cm. Highest dust fluxes occurred at the devegetated site, followed by the playa, a mesquite site with unvegetated {\textquoteleft}{\textquoteleft}streets,{\textquoteright}{\textquoteright} and tarbush sites.
These field observations are consistent with laboratory-based dust emission experiments and remote sensing studies in the Chihuahuan Desert. Playas and tarbush sites are major dust producers due to high proportions of fines, whereas the mesquite site produces much dust because of greater overall mass flux. Mesquite dunes covering most of the basin likely produce the most dust overall, though playas and tarbush-
dominated alluvial flats (which cover about 8\%) can emit large amounts of dust. Continuing shrubland encroachment will likely increase dust emissions from the Jornada Basin, as well as in other arid regions. {\textcopyright} 2011 Elsevier B.V. All rights reserved.10.1016/j.aeolia.2011.02.002

}, keywords = {BSNE, Chihuahuan Desert, dust collection, dust flux, Jornada Basin LTER, land cover, NPP sites, particle size, sand transport, vegetation communities}, doi = {10.1016/j.aeolia.2011.02.002}, url = {files/bibliography/JRN00587.pdf}, author = {Floyd, Kevin W. and Thomas E. Gill} } @article {49969, title = {Foraging behavior of heritage versus recently introduced herbivores on desert landscapes of the American Southwest}, journal = {Ecosphere}, volume = {2}, year = {2011}, month = {05/2011}, pages = {1-14}, chapter = {Article 57}, abstract = { Since the 1800s managed grasslands and shrublands of the arid American Southwest have been grazed predominantly by cattle originally bred for temperate climates in northern Europe. A heritage breed, the criollo cattle, has survived in northern Mexico for more than 400 years under desert-like conditions of low and variable rainfall, hot temperatures in the growing season, and both spatially and temporally scarce levels of primary production. We tested the hypothesis that the heritage breed has a broader spatial foraging distribution under harsh environmental conditions, and that its distribution is driven by environmental variables which differ from those that control the distribution of the introduced European breed. Movements of individual criollo and Angus breed animals were monitored autonomously in the northern Chihuahuan desert of southern New Mexico, USA. Georeferenced foraging locations acquired at 5-minute intervals for each animal were fit to a logistic regression using environmental factors as predictors. In the spring, when forage availability was high and more uniformly distributed across the landscape, animal foraging patterns were similar for both breeds. In the fall when forage availability was low and non-uniformly distributed, the two breeds exhibited very different foraging patterns: heritage animals foraged across a much larger spatial extent whereas their domestic counterparts remained in close proximity to the permanent source of water. These differences in foraging behavior driven by environmental variables have important implications for sustainability of rangelands in spatially and temporally variable environments. Heritage breeds of animals that are generalist foragers during unfavorable conditions can reduce environmental impacts compared to more recently introduced breeds.}, keywords = {Chihuahuan Desert, criollo cattle, GPS monitoring, herbivory, landscape foraging patterns, resource selection functions}, doi = {doi:10.1890/ES11-00021.1}, url = {/files/bibliography/11-009.pdf}, author = {H. Raul Peinetti and E.L. Fredrickson and Debra C. Peters and Andr{\'e}s F. Cibils and Roacho-Estrada, J.O. and Andrea S. Laliberte} } @proceedings {49981, title = {Plant-soil feedbacks and the reversal of desertification with climate change}, year = {2011}, month = {04/2011}, pages = {292-296}, publisher = {International Rangeland Congress}, address = {Rosario, Argentina}, abstract = {Our objective was to provide a conceptual framework for perennial grass recovery in a series of wet years, which includes both plant-soil feedbacks that increase available water to grasses and effects of precipitation on a sequence of recovery-related processes. We tested hypotheses based on this framework for grasslands and shrublands in the Chihuahuan Desert, the largest desert in North America. Results show that a sequence of 5 wet years following 14 years of variable rainfall increased production in resource conserving ecosystem types greater than predicted based on rainfall alone. The increase in production was primarily by herbaceous plants, which captured water locally to increase plant available water to both existing plants and new recruits. The sequence of wet years allowed a series of linked plant processes to occur that resulted in the establishment and survival of perennial grasses and forbs. We predict that a continued series of wet years will maintain the herbaceous component of these systems, and may act to reverse desertification on degraded shrublands, and to maintain perennial grasslands without management inputs. Degraded shrublands located on slopes susceptible to runoff of water responded linearly to annual precipitation in multiple wet years, and are expected to be resistant to a shift back towards grasslands under a directional increase in precipitation.}, keywords = {Chihuahuan Desert, grasslands, precipitation, regime shift, shrublands}, url = {/files/bibliography/11-017.pdf}, author = {Debra C. Peters and Jin Yao and John P. Anderson and O. E. Sala} } @mastersthesis {49997, title = {Insights on seasonal fluxes in a desert shrubland watershed from a distributed sensor network}, year = {2011}, pages = {171}, school = {Arizona State University}, type = {Masters}, abstract = {

\ \ \ \  The North American Monsoon System (NAMS) contributes ~55\% of the annual rainfall in the Chihuahuan Desert during the summer months. Relatively frequent, intense storms during the NAMS increase soil moisture, reduce surface temperature and lead to runoff in ephemeral channels. Quantifying these processes, however, is difficult due to the sparse nature of coordinated observations.
\ \ \ \  In this study, I present results from a field network of rain gauges (n = 5), soil probes (n = 48), channel flumes (n = 4), and meteorological equipment in a small desert shrubland watershed (~0.05 km2) in the Jornada Experimental. Using this high-resolution network, I characterize the temporal and spatial variability of rainfall, soil conditions and channel runoff within the watershed from June 2010 to September 2011, covering two NAMS periods. In addition, CO2, water and energy measurements at an eddy covariance tower quantify seasonal, monthly and event-scale changes in land-atmosphere states and fluxes.
\ \ \ \  Results from this study indicate a strong seasonality in water and energy fluxes, with a reduction in Bowen ratio (B, the ratio of sensible to latent heat fluxes) from winter (B = 14) to summer (B = 3.3). This reduction is tied to shallow soil moisture availability during the summer (s = 0.040 m3/m3) as compared to the winter (s = 0.004 m3/m3). During the NAMS, I analyzed four consecutive rainfall-runoff events to quantify the soil moisture and channel flow responses and how water availability impacted the land-atmosphere fluxes. Spatial hydrologic variations during events occur over distances as short as ~15 m.
\ \ \ \  The field network also allowed comparisons of several approaches to estimate evapotranspiration (ET). I found a more accurate ET estimate (a reduction of mean absolute error by 38\%) when using distributed soil moisture data, as compared to a standard water balance approach based on the tower site. In addition, use of spatially-varied soil moisture data yielded a more reasonable relationship between ET and soil moisture, an important parameterization in many hydrologic models. The analyses illustrates the value of high-resolution sampling for quantifying seasonal fluxes in desert shrublands and their improvements in closing the water balance in small watersheds.

}, keywords = {carbon dioxide flux, Chihuahuan Desert, CO2 flux, eddy covariance, evapotranspiration, hydrology, NAMS, North American Monsoon System, rainfall, runoff, soil moisture, soil temperature, Tromble Weir Watershed}, url = {files/bibliography/JRN00569.pdf}, author = {Ryan Templeton} } @conference {50009, title = {Grassland restoration following mesquite invasion in the northern Chihuahuan Desert: Persistence, patience, and perspectives from the past and present}, booktitle = {Society for Range Management}, volume = {63rd Society for Range Management}, year = {2010}, pages = {Sym-22}, address = {Denver, CO}, abstract = {The widespread invasion of grasslands by woody plants in the northern Chihuahuan Desert over the past 100-150 years is well-documented, and has stimulated a large body of research about the mechanisms driving this conversion, as well as approaches to grassland restoration. Progressive invasion and eventual domination by mesquite (Prosopis glandulosa Torr.) is often associated with dramatic redistribution of soils, loss of herbaceous cover, and severely reduced ecological function. Restoration in this region is problematic due to low soil moisture availability and the instability of mesquite-dominated communities, particularly on coarse sandy soils. Historical efforts to rehabilitate invaded sites initially focused on implementing individual control methods and reseeding to restore vegetation structure. Progressively, the focus of restoration research has incorporated integrated management approaches aimed at recovering both structure and function. We provide a brief review of historical approaches, lessons learned, and the results of recent research involving simultaneous manipulations of vegetation, soils, and the soil seedbank.}, keywords = {Chihuahuan Desert, ecological, restoration}, author = {Laurie Abbott and Jeffrey E. Herrick and Kendal Young} } @article {JRN52698, title = {Rapid response of a grassland ecosystem to an experimental manipulation of a keystone rodent and domestic livestock}, journal = {Ecology}, volume = {91}, year = {2010}, month = {2010}, pages = {3189-3200}, chapter = {3189}, abstract = {

Megaherbivores and small burrowing mammals commonly co-exist and play important functional roles in grassland ecosystems worldwide. The interactive effects of these two functional groups of herbivores in shaping the structure and function of grassland ecosystems are poorly understood. In North America\’s central grasslands, domestic cattle (Bos taurus) have supplanted bison (Bison bison), and now co-exist with prairie dogs (Cynomys spp.), a keystone burrowing rodent. Understanding the ecological relationships between cattle and prairie dogs and their independent and interactive effects is essential to understanding the ecology and important conservation issues affecting North American grassland ecosystems. To address these needs, we established a long-term manipulative experiment that separates the independent and interactive effects of prairie dogs and cattle using a 2 x 2 factorial design. Our study is located in the Janos-Casas Grandes region of northwestern Chihuahua, Mexico, which supports one of the largest remaining complexes of black-tailed prairie dogs (C. ludovicianus). Two years of post-treatment data show nearly 2-fold increases in prairie dog abundance on plots grazed by cattle compared to plots without cattle. This positive effect of cattle on prairie dogs resulted in synergistic impacts when they occurred together. Vegetation height was significantly lower on the plots where both species co-occurred compared to where either or both species was absent. The treatments also significantly affected abundance and composition of other grassland animal species, including grasshoppers and banner-tailed kangaroo rats. Our results demonstrate that two different functional groups of herbivorous mammals, burrowing mammals and domestic cattle, have distinctive and synergistic impacts in shaping the structure and function of grassland ecosystems.

}, keywords = {cattle, Chihuahuan Desert, ecosystem engineers, grasshoppers, grassland, grazing, herbivores, keystone species, prairie dogs, vegetation}, url = {/files/bibliography/10-038.pdf}, author = {A.D. Davidson and Ponce, Ed and David C. Lightfoot and E.L. Fredrickson and Joel R. Brown and Burzado, J. and David P. Toledo and S.L. Brantley and Sierra, R. and Lisk, R. and G. Ceballos} } @article {50021, title = {Spatial and temporal variability of plant-available water in calcium carbonate-cemented soils and consequences for arid ecosystem resilience}, journal = {Oecologia}, volume = {163}, year = {2010}, note = {August 14, 2008-Ecology; resubmitted to Oecologia 3-19-2009 w/new title}, pages = {215-226}, chapter = {215}, abstract = {

Increased variability in precipitation, including frequency of drought, is predicted for many arid and semiarid regions of the world. The ability of soils to retain water can increase resilience by buffering vegetation communities against precipitation extremes. Little is known, however, about water retention by carbonate cemented soil horizons, which occur extensively in arid and semiarid ecosystems. It has been speculated that they may significantly modify vertical and temporal distribution of plant-available water (PAW). To investigate this hypothesis, PAW was monitored at three sites in a mixed shrub-grass community in southern New Mexico, USA, across soils with differing degrees of carbonate horizon development: no carbonate horizon, a partially cemented calcic horizon, and a continuously cemented petrocalcic horizon. Results are presented from three years that included extremely dry and wet periods. Calcic and petrocalcic horizons absorbed and retained significantly greater amounts of PAW for several months following an extremely wet winter and summer compared to the non-carbonate soil. Following a wet summer, petrocalcic horizons retained very high PAW (16 to 18\% volumetric or ~72 to 80\% of soil water holding capacity) through early spring of the following year, more than double the PAW retained by similar depths in the non-carbonate soil. Drying dynamics indicate calcic and petrocalcic horizons release stored water into the grass rooting zone during growing seasons following extreme events. Water dynamics of calcic and petrocalcic horizons during extreme events provide a mechanism to explain previous observations that perennial grasses exhibit greater resilience to drought when high carbonate horizons occur at shallow depths (\< 50 cm). Water holding capacity of the entire profile, including rock-like material such as calcium carbonate, should be considered when evaluating the potential resilience of vegetation communities to disturbance, including the increased variability in precipitation expected to occur as a result of global climate change.

}, keywords = {calcic, Chihuahuan Desert, climate change, desert grassland, ecosystem, horizon, Petrocalcic, precipitation}, doi = {10.1007/s00442-009-1530-7}, url = {/files/bibliography/10-03.pdf}, author = {Danielle Duni and Jeffrey E. Herrick and Curtis H. Monger} } @article {50091, title = {Camel spider (Solifugae) use of prairie dog colonies}, journal = {Western North American Naturalist}, volume = {69}, number = {2}, year = {2009}, month = {07/2009}, pages = {272-276}, chapter = {272}, abstract = {

Solifugids (camel spiders) are widespread throughout arid regions of western North America and are thought to be important in structuring desert arthropod communities. Despite the ubiquity of camel spiders, little is known about their ecology. Black-tailed prairie dogs (Cynomys ludovicianus) are also widespread in western North America and are important ecosystem engineers, but they have been reduced in extent because of human activity. Here we report significantly greater numbers of camel spiders on black-tailed prairie dog colonies in southern New Mexico. The difference in vegetation structure created by prairie dog activity is likely the reason for the increased prevalence of camel spiders on colonies. Because camel spiders are important predators and prey, the observation that colonies support higher numbers of these animals provides a mechanism explaining differences in arthropod communities on and off colonies and explaining the preferential foraging behavior of vertebrates associated with prairie dog colonies.

}, keywords = {black-tailed prairie dogs, Chihuahuan Desert, ecosystem engineering, grassland ecology, Solifugae}, doi = {10.3398/064.069.0220}, url = {/files/bibliography/09-018.pdf}, author = {B.D. Duval and Walter G. Whitford} } @article {50094, title = {Animal disturbances promote shrub maintenance in a desertified grassland}, journal = {Journal of Ecology}, volume = {97}, year = {2009}, note = {//NMSU,USDA//LTER V//entered 10/14/2009; pdf available}, month = {2009}, pages = {1302-1310}, chapter = {1302}, abstract = {

Soil disturbance by animals affects the availability of water, nutrients, sediment and seeds, which are critical for the maintenance of functional ecosystems. We examined long-lived faunal structures across six vegetation communities in the northern Chihuahuan desert of New Mexico, USA, testing the proposition that disturbances in undesertified grassland differ in magnitude and effect from those in desertified grassland.\  Vertebrate and invertebrate disturbances totalled 18.9 structures ha)1 across 18 sites. The most common were pits and mounds of American badgers (Taxidea taxus, 32\%), nests of the ant Aphaenogaster cockerelli (18.8\%) and mounds of kangaroo rats (Dipodomys spectabilis, 31\%).\  Desertification was associated with a doubling of the density of structures, but no effects on cover or volume. The greatest density was in desertified mesquite and creosote bush shrublands, and the lowest density in undesertified grass swales. Badger and wood rat (Neotoma sp.) mounds were significant indicators of desertified communities. Desertification did not affect the density of kangaroo rat mounds (6.7 ha)1 in black grama grasslands and creosote bush shrublands). However, mounds in creosote bush shrubland were smaller and had more and larger shrubs than adjacent inter-mound hummocks. Desertification was associated with increases in the density of Aphaenogaster cockerelli and Trachymyrmex smithii nests, and declines in Pogonomyrmex rugosus nests. Substantial increases in soil nitrate and electrical conductivity on Myrmecocystus nests were associated with desertification. Synthesis. Desertification shaped this desert environment in two main ways. First, while kangaroo rat mound density changed little with desertification, mounds in shrubland continued to enhance shrub persistence long after abandonment, reinforcing desertification processes. Second, marked changes in the density of nests of the key ant species altered the spatial distribution of soil nitrate and electrical conductivity, likely affecting soil fertility and the distribution of desert plants. Our results highlight the importance of animal activity in shaping desert plant communities, and in maintaining or reinforcing desertification processes.

}, keywords = {animal activity, article, Biopedturbation, Chihuahuan Desert, desertification, disturbance, ecosystem engineering, journal, pedogenesis}, doi = {10.1111/j.1365-2745.2009.01558.x}, url = {/files/bibliography/10-036.pdf}, author = {D.J. Eldridge and Walter G. Whitford and B.D. Duval} } @article {50123, title = {Scale and the isotopic reocrd of C4 plants in pedogenic carbonate: from the biome to the rhizosphere}, journal = {Ecology}, volume = {90}, number = {6}, year = {2009}, note = {//USDA,OTHER//LTER V//entered 07/13/2009; pdf available}, month = {2009}, pages = {1498-1511}, abstract = {The 13C/12C ratio in pedogenic carbonate (i.e., CaCO3 formed in soil) is a significant tool for investigating C4 biomes of the past. However, the paleoecological meaningof d13C values in pedogenic carbonate can change with the scale at which one considers the data. We describe studies of modern soils, fossil soils, and vegetation change in the Chihuahuan Desert of North America and elsewhere that reveal four scales important for paleoecologic interpretations. (1) At the broadest scale, the biome scale (hundreds to millions of km2), an isotopic record interpreted as C3 vegetation replacing C4 grasslands may indicate invading C3 woody shrubs instead of expanding C3 forests (a common interpretation). (2) At the landscape scale (several tens of m2 to hundreds of km2), the accuracy of scaling up paleoclimatic interpretations to a regional level is affected by the landform containing the isotopic record. (3) At the soil-profile scale (cm2 to m2), soil profiles with multiple generations of carbonate mixed together have a lower-resolution paleoecologic record than soil profiles repeatedly buried. (4) At the rhizosphere scale (lm2 to cm2), carbonate formed on roots lack the 14{\textendash}17{\o} enrichment observed at broader scales, revealing different fractionation processes at different scales. A multi-scale approach in dealing with d13C in pedogenic carbonate will increase the accuracy of paleoecologic interpretations and understanding of soil{\textendash}geomorphic{\textendash}climatic interactions that affect boundaries between C4 and C3 vegetation.}, keywords = {article, C3 vs C4 vegetation, carbon isotopes, Chihuahuan Desert, climate change, desertification, Jornada Experimental Range, journal, landscape ecology, pedogenic carbonate, peleoclimate, peleoecology, soil-geomorphic-clmatic interaction, southern New Mexico, USA}, author = {Curtis H. Monger and David R. Cole and B. J. Buck and R. A. Gallegos} } @article {50202, title = {Resource regulation by a twig-girdling beetle has implications for desertification}, journal = {Ecological Entomology}, volume = {33}, year = {2008}, note = {//USDA//LTER V//entered 04/03/2008}, month = {2008}, pages = {161-166}, abstract = {

1. Resource regulation by insects is the phenomenon by which herbivory enhances resources for the progeny of the herbivore. This report provides an example of resource regulation with implications for desertification in the Chihuahuan Desert of North America.

2. Female Oncideres rhodosticta beetles chew girdles around mesquite ( Prosopis glandulosa ) stems before ovipositing in those stems. The mesquite plants respond by producing compensatory stems below the girdle. Mesquite volume was significantly correlated with the total number of beetle girdles across a suite of low shrub density grassland and high shrub density dune sites, and plants in dune sites had more old and new girdles than mesquite in grasslands.

3. Smaller, younger shrubs in grassland responded more vigorously to girdling than did larger, older shrubs in dune landscapes. Stems on shrubs within grassland produced significantly more and longer compensatory stems per girdle than stems on shrubs in dunes. Soil capture by individual plants positively correlated with stem density, and stem density is increasing in the younger plants as a response to beetle damage.

4. This study suggests that the interaction between O. rhodosticta and mesquite is an example of resource regulation that increases the stem density and soil capture ability of mesquite. Because the conversion of productive grasslands to mesquite dune landscapes is one of the most important drivers of desertification in the Chihuahuan Desert, feedbacks between organisms that promote an increase in the size and soil capture ability of mesquite may exacerbate desertification.

}, keywords = {arthropod, mesquite, arthropod, Prosopis, article, Chihuahuan Desert, desertification, resource regulation, journal, landscape conversion, Oncideres, plant-herbivore interactions, Prosopis}, doi = {10.1111/j.1365-2311.2007.00928.x}, url = {files/bibliography/JRN00511.pdf}, author = {B.D. Duval and Walter G. Whitford} } @conference {50207, title = {Landscape histories, livestock management, and mesquite expansion in the Chihuahuan Desert of New Mexico}, booktitle = {Society for Range Management Annual Meeting}, year = {2008}, month = {January 26, 2008}, pages = {2188}, address = {Louisville, KY}, abstract = {During the past 125 years the northern Chihuahuan Desert has undergone a significant shift from desert grasslands to desert shrub conditions, with mesquite (Prosopis glandulosa) dramatically increasing in dominance during this period. The transition from desert grasslands is viewed as deleterious, decreasing forage availability for both wildlife and livestock while negatively impacting air, water, and soil processes that support ecosystem services important to rapidly growing, human populations. Causes leading to this transition include formulation of government and industry policies, and later application of some range management principles, without an understanding of the evolutionary and landscape history of the northern Chihuahuan Desert. In addition, as causes of mesquite expansion were determined, primary factors leading to mesquite{\textquoteright}s eventual dominance did not receive adequate attention, most likely because they did not fit within dominant scientific paradigms, or social-political realities of the time. Future work needs to focus on better understanding evolutionary and landscape legacies of this region; including factors that created and maintained the original desert grasslands prior to desert scrub conditions. Using this understanding we must create appropriate theory that will guide future human-ecological interactions and assessment of ecological trajectories. This knowledge must affect policy and eventual management. We must relax the need for ecosystems to adapt to human behaviors and consider how human behaviors can best adapt to the ecosystems on which they depend.}, keywords = {Chihuahuan Desert}, author = {E.L. Fredrickson and Jeffrey E. Herrick and H. Raul Peinetti and Andrea S. Laliberte} } @conference {50235, title = {Rodent density and the landscape of fear in the Chihuahuan Desert}, booktitle = {93rd Ecological Society of America Annual Meeting}, series = {93rd ESA Annual Meetings}, year = {2008}, month = {August 3-8, 2008}, pages = {COS 118-8}, abstract = {Small mammals in desert environments are important links in ecosystem energy flow, with their densities often effecting the abundance of their primarily predators. Granivorous small mammals also affect seed dispersal and can shape vegetation characteristics. Consequently, factors affecting small mammal abundance are important in understanding community and ecosystem structure and dynamics. Small mammal abundance has been attributed to levels of precipitation/primary productivity (bottom up) and/or removal by predation (top down). However, small mammal abundance can vary greatly over the landscape in relatively short (< 5 km) distances. Similarities in precipitation amounts and predator abundance on this small scale do not explain this within-landscape variation in abundance. However, on this scale, habitat heterogeneity can be high. Under the landscape of fear model, such habitat heterogeneity can result in proportionally different amounts of safe vs risky habitat and consequently, predation risk among adjacent areas. We predicted that density of small mammals in an area is inversely related to the proportion of risky habitat/level of predation risk of an area. We tested this prediction with kangaroo rats (Dipodomys spp.) in two geographically separate areas of the Chihuahaun Desert: Mapimi Biosphere reserve in Durango Mexico and the Jornada Experimental range in New Mexico. We measured giving up densities (GUDs) in 8 distinct areas of similar shrub/grass habitat with different densities of kangaroo rats. GUD{\textquoteright}s were measured with commercial 50 x30 x 10 cm aluminum buffet trays containing 3 kg of sand and 4 g of millet seed. The specific prediction was that GUDs would be inversely related to kangaroo rat densities.}, keywords = {abstract, Chihuahuan Desert, desnity, rodent}, author = {John W. Laundre and Lucina Hern{\'a}ndez and A. Campanella and D. K. James} } @conference {50307, title = {Linking ground observations, simulation model output, and remote sensing data to characterize phenology across diverse arid landscapes}, booktitle = {American Society of Photogrammetry and Remote Sensing Meetings}, series = {Southwest Region}, year = {2007}, month = {October 5, 2007}, abstract = {We combined long-term data on plant phenology with simulation modeling output and remote sensing data to characterize diverse landscapes at the Jornada Experimental Range in the northern Chihuahuan Desert of southern New Mexico. Phenology of 15 key species in Chihuahuan Desert plant communities have been monitored monthly for 15 sites since 1992. Phenological state (non-reproductive, in bud, in flower, dormant) is noted for all plants of selected grass and shrub species at three replicate sites of five major plant communities (upland grasslands, playa grasslands, creosotebush shrublands, mesquite shrublands, tarbush shrublands). We combined these long-term data with simulation model results of key species to extrapolate back in time and to forecast future dynamics under a changing climate. We used a daily timestep model of soil water dynamics (SOILWAT) to simulate recruitment of the dominant grass for the entire Jornada Basin. We also compared the long-term data with remotely sensed images through time for one year from the ASTER satellite. The ability of the ASTER images to sense phonological changes varied by community type. Linking different technologies has great potential for improving understanding and prediction for arid landscapes that vary both temporally and spatially.}, keywords = {Chihuahuan Desert, phenology, remote sensing, simulation}, author = {John P. Anderson and Debra C. Peters and A. Rango and Caitriana Steele} } @article {50313, title = {Does shrub invasion indirectly limit grass establishment via seedling herbivory? A test at grassland-shrubland ecotones}, journal = {Journal of Vegetation Science}, volume = {18}, year = {2007}, month = {March 1, 2007}, pages = {363-370}, abstract = {Does shrub invasion at ecotones indirectly limit grass establishment by increasing mammalian seedling herbivory, Chihuahuan Desert, New Mexico? We tested the hypothesis that herbivore-related mortality of seedlings of the dominant perennial grass Bouteloua eriopoda would be highest in shrub-dominated portions of grassland-shrubland ecotones. We tested the hypothesis in two Chihuahuan Desert sites featuring similar shrub encroachment patterns but different shrub species, grass cover, and different abundances of small mammals. Within each site we transplanted B. eriopoda seedlings to grass-dominated, middle, and shrub-dominated positions of replicate ecotones during the time of year (mid-summer) when they would naturally appear and monitored seedling fates. We estimated population size/activity of putative small mammal herbivores. Seedlings were killed by mammals in greater number in shrubland than in grassland or middle ecotone positions at the site withlarge herbivore numbers. At the site with low herbivore numbers, most seedlings were killed in middle ecotone positions. The abundance patterns of herbivores did not parallel patterns of seedling herbivory across the ecotones or between sites. Seedling herbivory is an improtant process and is related to vegetation composition, but the mechanisms underlying the relationship are not clear. We speculate that variation in small mammal foraging behvior may contribute to seedling herbivory patterns. Restoration strategies in the Chihuahuan Desert need to account for the abundance and/or behavior of native herbivores.}, keywords = {alternative state, Bouteloua eriopoda, Chihuahuan Desert, desertifiction, Dipodomys, foraging behavior, Lepus californicus, restoration, small mammal}, url = {/files/bibliography/07-005.pdf}, author = {Brandon T Bestelmeyer and Khalil, N.I. and Debra C. Peters} } @conference {50320, title = {Rodent community landscape ecology in grassland-shrubland ecotones and gradients in the Chihuahuan Desert}, booktitle = {22nd Annual Symposium of U.S. Regional Chapter of International Association of Landscape Ecology}, year = {2007}, month = {April 9-11, 2007}, pages = {p. 21}, address = {Tucson, AZ}, abstract = {It is believed that the abundance and diversity of Chihuahuan Desert rodents increases with shrub encroachment accompanying desertification although grassland specialist species decline with loss of perennial grasses. It has been reported, however, that rodent population responses to spatial variation in habitat are mediated by a complex suite of biotic-abiotic interactions. The consistency of such patterns across a landscape has not been examined. We tested the hypothesis that rodent richness, biomass, and density/abundance were highest in shrub-dominated portions of replicate grassland-shrubland ecotones and across a grassland-shrubland gradient. Rodents were trapped on permanent grids scattered over an area of 200 km2. Mark-recapture procedures were used to estimate population density and the software eCognition to estimate landscape structure using an object-oriented spatial analysis approach. We found that rodent abundance, biomass, and species composition were highly variable and related to the details of vegetation structure across the landscape, rather than being simply positively correlated with shrub cover.}, keywords = {Chihuahuan Desert, diversity, rodent}, author = {A. Campanella and Brandon T Bestelmeyer and G. Roemer and Debra C. Peters} } @conference {50334, title = {Using the GIS to study the past and present of a northern Chihuahuan Desert playa}, booktitle = {60th Annual Meeting and Trade Show, Society for Range Management}, year = {2007}, month = {02/09/2007}, pages = {Paper No. 179}, address = {Sparks/Reno, NV}, abstract = {The encroachment of mesquite (Prosopis glandulosa Torr.) and other desert shrubs into the desert grasslands of the northern Chihuahuan Desert is commonly associated with increased rates of soil erosion. The processes associated with vegetation shifts are still poorly understood. One such example of vegetation shift is the replacement of tobosa (Pleuraphis mutica Buckely) grasslands by mesquite dunelands on the Red Lake playa, an ephemeral lake on the USDA-ARS Jornada Experimental Range in south central New Mexico, USA. The objective of this project was to describe grass-shrubland transitions for vegetation patches based on soil characteristics and spatial context. We used aerial photos from 1942 and 1973 and a digital orthophoto quarter quadrangle from 1996 to define changes in the mesquite-dominated area since 1942. We used the 1996 photos to compare GIS-based mesquite canopy intercept measurements with line-point and canopy intercept measurements completed in 2005. We then used a QuickBird satellite image from 2004 to identify current vegetation community patches based on vegetation type, soil reflectance, and the spatial distribution of plants and bare ground within each patch. Plots were then established in the field within these patches to characterize the soils and vegetation of the site and create highly-detailed soil and vegetation maps of the site. After the initial characterization, the field data and 2004 satellite image were compared against the older imagery and past vegetation and soil maps to identify areas requiring more intensive soil and vegetation measurements. We plan to use these data to identify relationships between various soil properties and vegetation community composition and structure. This information will be used on patterns and processes to propose changes to state-and-trainsition models correlated with soils in this area.}, keywords = {Chihuahuan Desert, GIS, mesquite, soil erosion}, author = {N.K. Hansen and Jeffrey E. Herrick and Laurie Abbott and Debra C. Peters and D. Parker} } @article {50358, title = {Calcium carbonate in termite galleries {\textendash} biomineralization or upward transport?}, journal = {Biogeochemistry}, volume = {82}, year = {2007}, note = {//NMSU, USDA//LTER V//entered 06/14/2007}, month = {2007}, pages = {241-250}, abstract = {

Termites and soil calcium carbonate are major factors in the global carbon cycle: termites by their role in decomposition of organic matter and methane production, and soil calcium carbonate by its storage of atmospheric carbon dioxide. In arid and semiarid soils, these two factors potentially come together by means of biomineralization of calcium carbonate by termites. In this study, we evaluated this possibility by testing two hypotheses. Hypothesis 1 states that termites biomineralize calcium carbonate internally and use it as a cementing agent for building aboveground galleries. Hypothesis 2 states that termites transport calcium carbonate particles from subsoil horizons to aboveground termite galleries where the carbonate detritus becomes part of the gallery construction. These hypotheses were tested by using (1) field documentation that determined if carbonate-containing galleries only occurred on soils containing calcic horizons, (2) 13C/12C ratios, (3) X-ray diffraction, (4) petrographic thin sections, (5) scanning electron microscopy, and (6) X-ray mapping. Four study sites were evaluated: a C4-grassland site with no calcic horizons in the underlying soil, a C4-grassland site with calcic horizons, a C3-shrubland site with no calcic horizons, and a C3-shrubland site with calcic horizons. The results revealed that carbonate is not ubiquitously present in termite galleries. It only occurs in galleries if subsoil carbonate exists within a depth of 100 cm. 13C/12C ratios of carbonate in termite galleries typically matched 13C/12C ratios of subsoil carbonate. X-ray diffraction revealed that the carbonate mineralogy is calcite in all galleries, in all soils, and in the termites themselves. Thin sections, scanning electron microscopy, and X-ray mapping revealed that carbonate exists in the termite gut along with other soil particles and plant opal. Each test argued against the biomineralization hypothesis and for the upward-transport hypothesis. We conclude, therefore, that the gallery carbonate originated from upward transport and that this CaCO3 plays a less active role in short-term carbon sequestration than it would have otherwise played if it had been biomineralized directly by the termites.

}, keywords = {arid and semiarid soils, atmospheric carbon dioxide, carbon isotopes, carbon sequestration, Chihuahuan Desert, pedogenic carbonate, termite, calcium carbonate, termite, gallery construction}, isbn = {DOI: 0.1007/s10533-006-9067-x}, doi = {10.1007/s10533-006-9067-x}, url = {files/bibliography/07-Bgchmstry-Whitford.pdf}, author = {Liu, X. and Curtis H. Monger and Walter G. Whitford} } @inbook {50420, title = {A Holistic View of an Arid Ecosystem: A Synthesis of Research and Its Applications}, booktitle = {Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {354-368}, publisher = {Oxford University Press}, organization = {Oxford University Press}, chapter = {17}, address = {New York}, abstract = {A primary objective of the Jornada Long-Term Ecological Research (LTER) program has been to provide a broad view of desert grassland ecology. Early architects of the LTER program felt that existing ecological datasets were usually of too short a duration and represented too few ecosystem components to provide a foundation for predicting dynamics in response to disturbances (NSF 1979). This recognition gave rise to the LTER approach{\textemdash}using long-term and multidisciplinary research at particular places to advance a holistic and broad-scale, but also mechanistic, view of ecological dynamics. Such a view is essential to applying ecological research to natural resources management (Golley 1993; Li 2000). In this synthesis chapter we ask: What has this approach taught us about the structure and function of a desert grassland ecosystem? How should this knowledge change the way we manage arid ecosystems? What gaps in our knowledge still exist and why?}, keywords = {Chihuahuan Desert, desert grassland ecosystem, holistic view, Jornada Basin, LTER, multidisciplinary, patch-based correlations, research, synthesis book}, url = {/files/bibliography/06-068.pdf}, author = {Brandon T Bestelmeyer and Joel R. Brown and Kris Havstad and E.L. Fredrickson}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @article {50417, title = {Soil-Geomorphic Heterogeneity Governs Patchy Vegetation Dynamics at an Arid Ecotone}, journal = {Ecology}, volume = {87}, number = {4}, year = {2006}, month = {April 2006}, pages = {963-973}, abstract = {

Soil properties are well known to affect vegetation, but the role of soil heterogeneity in the patterning of vegetation dynamics is poorly documented. We asked whether the location of an ecotone separating grass-dominated and sparsely-vegetated areas reflected only historical variation in degradation or was related to variation in inherent soil properties. We then asked whether changes in the cover and spatial organization of vegetated and bare patches assessed using repeat aerial photography reflected self-organizing dynamics unrelated to soil variation or the stable patterning of soil variation. We found that the present-day ecotone was related to a shift from more weakly to more strongly developed soils. Parts of the ecotone were stable for over 60 year, but shifts between bare and vegetated states, as well as persistently vegetated and bare states, occurred largely in small (\<40 m2) patches throughout the study area. The probability that patches were presently vegetated or bare, as well as the probability that vegetation persisted and/or established over the 60 year period, was negatively related to surface calcium caronate and positively related to subsurface clay content. Thus, only a fraction of the landscape was susceptible to vegetation change and the sparesely-vegetated area likely featured a higher frequency of susceptible soil patches. Patch dynamics and self-organizing processes can be constrained by subtle (and often unrecognized) soil heterogeneity.

}, keywords = {autocorrelation, Chihuahuan Desert, patch dynamics, rangeland, self-organization, state-and-transition model, threshold}, doi = {10.1890/0012-9658(2006)87[963:SHGPVD]2.0.CO;2}, url = {/files/bibliography/06-015.pdf}, author = {Brandon T Bestelmeyer and J.P. Ward and Kris Havstad} } @article {50423, title = {Modeling flow patterns in a small vegetated area in the northern Chihuahuan Desert using QUIC (Quick Urban \& Industrial Complex)}, journal = {Environmental Fluid Mechanics}, volume = {6}, number = {4}, year = {2006}, note = {//USDA//LTER V//Entered 11/20/2006; updated 08/19/2008}, month = {2006}, pages = {359-384}, abstract = {

Sandstorms are frequent in the northern Chihuahuan Desert in New Mexico, an area characterized by open areas lacking vegetation, individual mesquite bushes, and mesquite coppice dunes. Field measurements of sand fluxes and wind velocities over a two year period provided a description of the area {\textendash} suggesting that the {\textquotedblleft}streets{\textquotedblright}, the flat, elongated, non-vegetated areas aligned with the dominant wind directions are the principal sources of wind-dispersed soil and dust. However, since soil erosion and dust movement depend on the pattern, strength, and gradients in the wind field, modeling soil erosion and dust movement requires a continuous wind velocity field. Consequently, air flow patterns at this site were simulated using a semi-empirical mass-consistent diagnostic wind field model: QUIC version 3.5 (Quick Urban \& Industrial Complex). Two hundred and fifty-one simulations were run encompassing several dust storms occurring in April 2003. Wind velocity vectors were compared between the model and field data at three heights for six locations and were found to correlate well for a majority of the situations suggesting that the flow patterns are consistent throughout the domain. In particular, good agreement was found for wind speeds at 0.75\ m, the height for which the model was tuned. However, it overestimated velocities at 1.5\ m (10\%) and 3.15\ m (13\%). Generally, the model successfully identified locations of the highest wind velocities and wind stresses, predominately found in {\textquotedblleft}streets{\textquotedblright} aligned with the driving wind, and locations of wake flow downwind of mesquite bushes where there was separation flow or otherwise shelter from the wind.

}, keywords = {aeolian processes, roughness elements, aeolian processes, vegetation effects, aeolian processes, wind erosion, aeolian processes, wind-transported dust, article, Chihuahuan Desert, desert vegetation, journal, mesquite, model, air flow patterns, model, QUIC, NPP sites, sand transport, wind modeling, wind steering}, doi = {10.1007/s10652-005-6021-8}, url = {files/bibliography/JRN00448.pdf}, author = {Bowker, George E. and D. E. Gillette and Gilles Bergametti and B{\'e}atrice Marticorena} } @article {50434, title = {Effects of altered temperature and precipitation on desert protozoa associated with biological soil crusts}, journal = {Journal of Eukaryotic Microbiology}, volume = {53}, number = {6}, year = {2006}, note = {//USDA//USGS//Entered 11/21/2006}, month = {2006}, pages = {507-514}, abstract = {Biological soil crusts are diverse assemblages of bacteria, cyanobacteria, algae, fungi, lichens, and mosses that cover much of arid land soils. The objective of this study was to quantify protozoa associated with biological soil crusts and test the response of protozoa to increased temperature and precipitation as is predicted by some global climate models. Protozoa were more abundant when associated with cyanobacteria/lichen crusts than with cyanobacteria crusts alone. Amoebae, flagellates, and ciliates originating from the Colorado Plateau desert (cool desert, primarily winter precipitation) declined 50-, 10-, and 100-fold, respectively, when moved in field mesocosms to the Chihuahuan Desert (hot desert, primarily summer rain). However, this was not observed in protozoa collected from the Chihuahuan Desert and moved to the Sonoran desert (hot desert, also summer rain, but warmer than Chihuahuan Desert). Protozoa in culture began to encyst at 37 1C. Cysts survived the upper end of daily temperatures (37{\textendash}55 1C), and could be stimulated to excyst if temperatures were reduced to 15 1C or lower. Results from this study suggest that cool desert protozoa are influenced negatively by increased summer precipitation during excessive summer temperatures, and that desert protozoa may be adapted to a specific desert{\textquoteright}s temperature and precipitation regime.}, keywords = {article, Chihuahuan Desert, climate change, Colorado Plateau, cryptobiotic crust, environmental stress, journal, soil change, soil function, soil crust, biological, soil fauna, soil food webs, soil protozoa, soil, ecosystem function, soil, food web, soil, methods, thermotolerance}, isbn = {DOI: 10.1111/j.1550-7408.2006.00134.x}, author = {Darby, Brian J. and Housman, David C. and Zaki, Amr M. and Shamout, Yassein and Adl, Sina M. and Jayne Belnap and Neher, Deborah A.} } @article {50444, title = {Wind characteristics of mesquite streets in the northern Chihuahuan desert, New Mexico, USA}, journal = {Environmental Fluid Mechanics}, volume = {6}, year = {2006}, month = {June 1, 2006}, pages = {241-275}, abstract = {

Past research has shown that the most important areas for active sand movement in the northern part of the Chihuahuan Desert are mesquite-dominated desert ecosystems possessing sandy soil texture. The most active sand movement in the mesquite-dominated ecosystems has been shown to take place on elongated bare soil patches referred to as {\textquotedblleft}streets{\textquotedblright}. Aerodynamic properties of mesquite streets eroded by wind should be included in explaining how mesquite streets are more emissive sand sources than surrounding desert land. To understand the effects of wind properties, we measured them at two {\textquoteright}at mesquite sites having highly similar soil textures but very different con{\textquoteright}gurations of mesquite. The differences in wind properties at the two sites were caused by differences of size, orientation, and porosity of the mesquite, along with the presence of mesquite coppice dunes (sand dunes stabilized by mesquites growing in the dune and on its surface) found only at one of the two sites. Wind direction, u{\textquoteright} (friction velocity), z0 (aerodynamic roughness height) and D (zero plane displacement height) were estimated for 15-m tower and 3-m mast data. These aerodynamic data allowed us to distinguish {\textquoteright}ve categories with differing potentials for sediment transport. Sediment transport for the {\textquoteright}ve categories varied from unrestricted, free transport to virtually no transport caused by vegetation protection from wind forces. In addition, {\textquotedblleft}steering{\textquotedblright} of winds below the level of the tops of mesquite bushes and coppice dunes allowed longer parallel wind durations and increased wind erosion for streets that aligned roughly SW{\textendash}NE. http://www.springerlink.com/content/y572665mn2j7n828/fulltext.pdf

}, keywords = {Chihuahuan Desert, desert vegetation, desert winds, dunes, dust emissions, flow around and above roughness elements, friction velocity, sand transport, vegetation}, doi = {10.1007/s10652-005-6022-7}, url = {/files/bibliography/06-026.pdf}, author = {D. E. Gillette and Jeffrey E. Herrick and Herbert, G.A.} } @inbook {50451, title = {Grazing Livestock Management in an Arid Environment}, booktitle = {Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {266-277}, publisher = {Oxford University Press}, organization = {Oxford University Press}, chapter = {13}, address = {New York}, abstract = {The history of livestock grazing in the Jornada Basin of southern New Mexico is a relatively recent story, but one of profound implications. For four centuries this region has supported a rangeland livestock industry, initially sheep, goats, and cattle, but primarily beef cattle for the past 130 years. Throughout this brief history of a domesticated ruminant in an ecosystem without a significant presence of large hoofed mammals as part of its evolutionary development, the livestock industry has continually grappled with high degrees of temporal and spatial variation in forage production. Management of this consumptive use, whether during Spanish, Mexican, United States Territorial, United States federal, or New Mexican governments, has constantly reaffirmed the need for grazing management to be flexible and responsive to the stress of droughts. The history of anecdotal experiences has been more recently augmented by scientific investigations first initiated in 1915. This chapter outlines the general history of livestock in this region, the historical specifics of ranching in the Jornada Basin, and resulting principles of grazing management derived from nearly a century of studies on grazing by large, domesticated herbivores.}, keywords = {Chihuahuan Desert, grazing, Jornada Basin, livestock management, LTER, synthesis book}, url = {/files/bibliography/06-064.pdf}, author = {Kris Havstad and E.L. Fredrickson and L. Huenneke}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @inbook {50448, title = {Introduction}, booktitle = {Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {3-14}, publisher = {Oxford University Press}, organization = {Oxford University Press}, chapter = {1}, address = {New York, NY}, abstract = {Arid lands throughout the world, including lands at the border of arid regions, are increasingly subject to human impact, leading to degradation of soils, losses of plant production, and a diminished economic potential to support human populations. Focusing on the human impact and consequent losses in economic potential, we often call these changes \"desertification.\" With the potential for global climate change, however, the definition of desertification and its potential must be expanded. Indeed, the 1992 United Nations\’ Desertification Convention defined desertification as \"land degradation in arid, semiarid and dry subhumid areas resulting from various factors, including climatic variations and human activities.\" It is more recently recognized that desertification involves human and environmental drivers but is a symptom evident at regional spatial scales that emerges from degradation at finer spatial scales. Assertions relative to an updated and revised paradigm regarding desertification have been developed. In l981, a group of scientists based in Las Cruces, New Mexico, and associated with New Mexico State University proposed a program of long-term ecological research in the Jornada Basin of southern New Mexico (USA) to gain a better understanding of processes that determine the structure and function of desert ecosystems. To an extent, this book represents both a synthesis of that effort and a benchmark of our progress over the last 23 years. In addition, this book draws on a longer history of research in the Jornada Basin that dates back to the early part of the twentieth century. Both the group and its mission have evolved since 1981, but an initial motivation for our studies was the dramatic, historic records of vegetation change in the Jornada.}, keywords = {Chihuahuan Desert, introduction, Jornada Basin, LTER, synthesis book}, url = {/files/bibliography/06-052.pdf}, author = {Kris Havstad and W. H. Schlesinger}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @booklet {50450, title = {Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {492}, publisher = {Oxford University Press}, address = {New York, NY}, abstract = {

This book is a synthesis of the arid rangeland research conducted in southern New Mexico for nearly a century. The Jornada Basin is truly a long-term research site, and this history is reflected in the databases described in many of the chapters in this book. Research in this basin formally began in 1912 with the creation by Presidential Order within the US Department of Agriculture of the 77,000-ha Jornada Range Reserve. Early publications, primarily USDA bulletins or journal articles in Ecology and the Botanical Gazette, appeared in print beginning in 1917. Researchers such as C.L. Forsling, J.T. Jardine, R.S. Campbell, and R.H. Canfield authored many of these early works, which are both classics in rangeland management and part of the foundation of studies decades later. The creation in 1927 of the Chihuahuan Desert Rangeland Research Center (initially known as the College Ranch) under the jurisdiction of New Mexico State University on 24,000 ha adjacent to the Jornada Range established the 101,000-ha area for long-term research in the basin that operates today. This history of research during the early twentieth century had numerous themes. Much of the early emphasis was on management related to agricultural production. Many of the principles that have been developed about livestock grazing management and rangeland improvement practices in the southwestern US and for arid lands in general can be traced to studies in the Jornada Basin. Yet, during these earlier decades there were also classic papers published on vegetation dynamics, resource redistribution, and small-mammal ecology. Over 40 years ago the first interdisciplinary studies were initiated; these studies served as a forerunner for the collaborative studies of the International Biological Programme (IBP) of the 1970s and those of the Jornada Basin that continue today. This 18-chapter book concludes with a description of future research for important issues in the twenty-first century

}, keywords = {Chihuahuan Desert, ecosystem, Jornada Basin, LTER, synthesis book}, url = {files/bibliography/JRN00461.pdf}, author = {Kris Havstad and L. Huenneke and W. H. Schlesinger}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @inbook {50459, title = {Remediation Research in the Jornada Basin: Past and Future}, booktitle = {Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {278-304}, publisher = {Oxford University Press}, organization = {Oxford University Press}, chapter = {14 }, address = {New York, NY}, abstract = {Land degradation in most of the Chihuahuan Desert is characterized by a shift from grass- to shrub-dominated plant communities. Consequently, most remediation efforts are focused on grassland restoration. Early experiments and trials focused on grazing management. Beginning in the 1930{\textquoteright}s and continuing through the 1980{\textquoteright}s, various methods of shrub control were evaluated. Early investigators had an intuitive and practical understanding of the system in which they worked. They saw the individual limitations to grassland recovery and attempted to address them. In order to be more successful than they were, we must begin to work at spatial and temporal scales relevant to the processes we hope to affect and target our interventions to those locations and during those periods when the processes are most susceptible to change. We must also, as the earlier workers did, simultaneously target multiple processes with the objective of increasing the resistance and resilience of the modified ecosystems.}, keywords = {Chihuahuan Desert, Jornada Basin, LTER, synthesis book}, url = {/files/bibliography/06-065.pdf}, author = {Jeffrey E. Herrick and Kris Havstad and A. Rango}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @inbook {50490, title = {Future Directions in Jornada Research: Applying an Interactive Landscape Model to Solve Problems}, booktitle = {Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {369-386}, publisher = {Oxford University Press}, organization = {Oxford University Press}, chapter = {18}, address = {New York, NY}, abstract = {In this book chapter, we propose a new model of arid and semiarid landscapes that focuses explicitly on the processes and properties that generate spatial variation in ecosystem dynamics. We are specifically interested in three interrelated aspects of landscapes: (1) feedbacks among plants, animals, and soils generated from interactions among biotic processes, a heterogeneous physical template, and the disturbance regime across a range of spatial and temporal scales, (2) neighborhood or contagious processes that generate fluxes and flows within and among spatial units, and (3) the landscape context and the condition of the study area of interest relative to its surroundings that modifies the transfers of materials. We first describe our spatially interactive model and compare it to previous models then introduce an approach to identify the landscape locations where spatial processes and information are needed in order to understand and predict ecosystem dynamics. The local, regional, and global implications of our interactive landscape model are also discussed.}, keywords = {Chihuahuan Desert, Jornada Basin, LTER, synthesis book}, url = {/files/bibliography/06-069.pdf}, author = {Debra C. Peters and W. H. Schlesinger and Jeffrey E. Herrick and L. Huenneke and Kris Havstad}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @inbook {50487, title = {Plant Communities in the Jornada Basin: The Dynamic Landscape}, booktitle = {Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {211-231}, publisher = {Oxford University Press}, organization = {Oxford University Press}, chapter = {10}, address = {New York, NY}, abstract = {Plant communities of the Jornada Basin LTER are characteristic of the northern Chihuahuan Desert, both in structure and dynamics. Five major vegetation types are often distinguished that differ in plant species cover and composition, as well as other factors, such as animal populations, soil properties, and elevation. Similar to many other parts of the Chihuahuan Desert, these plant communities have experienced major shifts in vegetation over the past 50-150 years. The most dramatic changes in vegetation have occurred as a result of woody plant encroachment into perennial grasslands. In this chapter, we describe the characteristics of each vegetation type and the documented changes in each type at the Jornada. We also discuss the key drivers (small and larger animal activity, drought, fire, and directional changes in climate) influencing these vegetation dynamics.}, keywords = {Chihuahuan Desert, Jornada Basin, LTER, synthesis book}, url = {/files/bibliography/06-061.pdf}, author = {Debra C. Peters and Gibbens, Robert P.}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @inbook {50507, title = {Patterns and Controls of Soil Water in the Jornada Basin}, booktitle = {Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {107-132}, publisher = {Oxford University Press}, organization = {Oxford University Press}, chapter = {5}, address = {New York, NY}, abstract = {This chapter focuses on the controls and patterns of soil moisture in the Jornada Basin. First, we describe general properties that commonly contribute to soil water heterogeneity; secondly, we offer a brief overview of soil water research in the Jornada Basin; and lastly, we describe specific patterns of soil water content and availability observed in the Jornada Basin. Our goal is to describe general patterns of soil water that are likely to occur across the Chihuahuan Desert region.}, keywords = {Chihuahuan Desert, Jornada Basin, LTER, synthesis book}, url = {/files/bibliography/06-056.pdf}, author = {K. A. Snyder and K. A. Mitchell and Jeffrey E. Herrick}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @inbook {50522, title = {Chihuahuan Desert Fauna: Effects on Ecosystem Properties and Processes}, booktitle = {Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {247-265}, publisher = {Oxford University Press}, organization = {Oxford University Press}, chapter = {12}, address = {New York, NY}, abstract = {This chapter addresses the direct and indirect effects of animals on ecosystem processes and/or their effects on ecosystem properties. This has been the primary focus of animal studies on the Jornada Experimental Range (JER) and the Chihuahuan Desert Rangeland Research Center (CDRRC) during the twentieth century. Early studies dealt with animal species that were thought to reduce the amount of primary production that was available to support livestock. With the establishment of the International Biological Programme (IBP) in the late 1960s and its premise that ecosystems could be modeled based on the energy flow conceptual model, animal studies were designed to measure energy flow through consumer populations. Those studies yielded estimates of consumption of live plant biomass between 1 and 10\% of the annual net primary production. It was concluded that, in most ecosystems, consumers process only a small fraction of the net primary production as live plant material and consumers play important roles in ecosystems as regulators of ecosystem processes and a less important role in energy flow. This hypothesis has been the focus of animal studies in the Jornada Basin for nearly 30 years. Studies of animals as regulators of ecosystem processes led to the expansion of this hypothesis to include the effects of animals on ecosystem properties. Expanding the spatial scale of studies from the patch to the watershed and landscape engendered hypotheses that animals have an effect on processes at those scales because of animal activities that affect redistribution of soil and organic matter.}, keywords = {Chihuahuan Desert, Jornada Basin, LTER, synthesis book}, url = {/files/bibliography/06-063.pdf}, author = {Walter G. Whitford and Brandon T Bestelmeyer}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @article {50548, title = {Desert grassland canopy arthropod species richness: temporal patterns and effects of intense, short-duration livestock grazing}, journal = {Journal of Arid Environments}, volume = {60}, number = {4}, year = {2005}, month = {March 1, 2005}, pages = {627-646}, abstract = {

Arthropods living in the canopies of two woody shrub species (a sub-shrub (Gutierrezia sarothrae) and a large shrub (Prosopis glandulosa)) and perennial grasses plus associated herbaceous species, were sampled on 18, 0.5 hectare plots in a Chihuahuan Desert grassland for five consecutive years. Mesquite shrubs were removed from nine plots, six plots were grazed by yearling cattle in August and six plots were grazed in February for the last 3 years of the 5 year study. Arthropod species richness ranged between 154 and 353 on grasses, from 120 to 266 on G. sarothrae, and from 69 to 116 on P. glandulosa. There was a significant relationship between the number of families of insects on grass and G. sarothrae and growing season rainfall but species richness was not a function of growing season rainfall on any of the plants. Several of the arthropod families that were the most species rich in this grassland were found on all of the plants sampled, i.e. Salticid spiders, Bruchid and Curculionid beetles, Cicadellid and Psyllid homopterans, and ants (Formicidae). There were more species rich families that were shared by grasses and the sub-shrub G. sarothrae than with mesquite. The absence of a relationship between growing season rainfall and species richness was attributed to variation in life history characteristics of arthropods and to the non-linear responses of annual and perennial desert grassland plants to rainfall.

There were no significant differences in insect family or species richness on any of the plant types as a result of removal of mesquite (P. glandulosa) from selected plots. Intense, short duration (24\ h) grazing by livestock during in late summer resulted in reduced species richness in the grass-herb vegetation layer but had no effect on insect species richness on snakeweed or mesquite shrubs. Livestock grazing in winter had no effect on insect species richness on any of the vegetation sampled.

}, keywords = {arthropods, canopy, Chihuahuan Desert, desert grassland, livestock grazing, species richness}, doi = {10.1016/j.jaridenv.2004.07.004}, url = {/files/bibliography/05-020.pdf}, author = {Gregory S. Forbes and Justin Van Zee and W. E. Smith and Walter G. Whitford} } @conference {50557, title = {Ecological sustainability in the Chihuahuan Desert: Is rangeland health relevant?}, booktitle = {Society for Range Management, 58th Annual Meeting and Trade Show}, year = {2005}, month = {February 5, 2005}, pages = {Paper No. 169}, address = {Fort Worth, TX}, abstract = {Rangeland health is increasingly promoted as a universal rangeland management objective. A protocol for interpreting indicators of rangeland health developed by a US interagency team has been extensively applied throughout the US and northern Mexico. A new version based on input from both the US and Mexico will be available in both Spanish and English in 2005. The protocol has been used to increase understanding of ecological properties and processes, and to assess the current status of those processes relative to their potential. While debates about the appropriate application of the protocol continue, it has been accepted and applied by many scientists and land managers in the US and Mexico. There has, however, been little critical evaluation of the relevance of either the specific protocol or the general concept of rangeland health to sustainability. The objectives of this paper are to provide an overview of the application of rangeland health on both sides of the border, and to critically evaluate not only its relevance to ecological sustainability, but also to socioeconomic sustainability, in order to better focus evaluations on those regions where management decisions are likely to be influenced by an increased understanding of rangeland health. We conclude that even a relatively rudimentary socioeconomic analysis may increase the cost-effectiveness of rangeland health evaluations.}, keywords = {Chihuahuan Desert, ecological properties and processes, ecological sustainability, rangeland health}, author = {Jeffrey E. Herrick and Foladori, G. and Melgoza, A.} } @conference {50626, title = {Endophytic fungi associated with shrubs and grasses of the northern Chihuahuan Desert and a potential role in drought tolerance}, booktitle = {Annual Meeting, Canadian Botanical Association}, year = {2004}, month = {June 26-30, 2004}, pages = {p. 10}, address = {Winnipeg, Manitoba, Canada }, abstract = {Native grasses and shrubs of the northern Chihuahuan Desert are predominantly colonized by dark septate endophytes. Methods using stains that target fungal chitin and internal lipids with high-magnification, light microscopy and scanning electron microscopy revealed a much greater incidence of colonization than was previously thought. In-vitro-regenerated plants from meristematic stem cells were also found to be colonized with the same fungi observed in plants from native populations. Originally thought to be restricted to roots, they are conspicuously present in meristems, sieve elements, xylem vessels of roots and leaves and in photsynthetic cells and stomata. Differing from pathogens and mycorrhizal fungi that have localized patterns of colonization, they systemically inhabit the entire apoplastic network of below- and aboveground organs. They encapsulate host cell protoplasts and are vertically transmitted by seed. Hyphal networks and biofilms that encapsulate all cells and tissues of micropropagated and native plants prevent their direct exposure to harsh external environments. The intimate nature of the association with all plant cells and organs indicates that these native desert shrubs and grasses function as composite plant-fungus organisms. A potential role in managing basic physiological processes that positively enhance plant survival in arid ecosystems is suggested.}, keywords = {Chihuahuan Desert, colonization, endophytes, fungi}, author = {J.R. Barrow and Aaltonen, R.E. and P. Osuna-Avila and I. Reyes-Vera} } @conference {50631, title = {Applications of multi- and cross-scale analyses to management of dynamic systems}, booktitle = {Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region}, year = {2004}, month = {October 15, 2004}, pages = {19}, address = {Alpine, TX}, abstract = {Decades of research on the management and monitoring of Chihuahuan Desert grasslands have emphasized (1) fine-scale patterns, (2) uniformity of dominant processes, and thus (3) standard, vegetation-based protocols for directing and measuring change. Although this was a necessary step, alone it is an insufficient approach to detecting and responding to degradation. We describe recent conceptual and empirical approaches to measuring the variety of pattern and process in vegetation transition based on soil-geomorphic-climate relationships, multiple scales of vegetation/soil pattern, and cross-scale interactions among grass loss in patches, patch connectivity and flux regulation, and climate-forcing functions. These approaches are being used to develop and refine tools that classify different pathways of vegetation response (state-and-transition models) according to soil and climate variables (ecological site descriptions). Pathways featuring cross-scale interactions can explain irreversible and nonlinear rates of change in time and space. These interactions indicate that different processes drive change at particular times and spatial locations, even within same vegetation type. Identification of the dominant processes governing vegetation change indicates the spatial pattern of change. In turn, this pattern indicates the appropriate scale and strategy for monitoring and designing and implementing management responses.}, keywords = {Chihuahuan Desert, climate, cross-scale, geomorphic, management, monitoring, multi-scale, soil, vegetation change}, author = {Brandon T Bestelmeyer and Jeffrey E. Herrick and Kris Havstad and E.L. Fredrickson and Joel R. Brown} } @article {50637, title = {Land management in the American Southwest: A state-and-transition approach to ecosystem complexity}, journal = {Environmental Management}, volume = {34}, number = {1}, year = {2004}, month = {July 1, 2004}, pages = {38-51}, abstract = {

State-and-transition models are increasingly being used to guide rangeland management. These models provide a relatively simple, management-oriented way to classify land condition (state) and to describe the factors that might cause a shift to another state (a transition). There are many formulations of state-and-transition models in the literature. The version we endorse does not adhere to any particular generalities about ecosystem dynamics, but it includes consideration of several kinds of dynamics and management response to them. In contrast to previous uses of state-and-transition models, we propose that models can, at present, be most effectively used to specify and qualitatively compare the relative benefits and potential risks of different management actions (e.g., fire and grazing) and other factors (e.g., invasive species and climate change) on specified areas of land. High spatial and temporal variability and complex interactions preclude the meaningful use of general quantitative models. Forecasts can be made on a case-by-case basis by interpreting qualitative and quantitative indicators, historical data, and spatially structured monitoring data based on conceptual models. We illustrate how science- based conceptual models are created using several rangeland examples that vary in complexity. In doing so, we illustrate the implications of designating plant communities and states in models, accounting for varying scales of pattern in vegetation and soils, interpreting the presence of plant communities on different soils and dealing with our uncertainty about how those communities were assembled and how they will change in the future. We conclude with observations about how models have helped to improve management decision-making.

}, keywords = {Chihuahuan Desert, community dynamics, desert grassland, grazing management, rangeland, resilience, simulation models, soil maps, thresholds}, doi = {10.1007/s00267-004-0047-4 }, url = {/files/bibliography/04-015.pdf}, author = {Brandon T Bestelmeyer and Joel R. Brown and Jeffrey E. Herrick and D. Trujillo and Kris Havstad} } @conference {50634, title = {Scales of pattern and process in the management of the Chihuahuan Desert biodiversity}, booktitle = {11th Annual Conference, The Wildlife Society}, year = {2004}, month = {September 18-22,}, address = {Calgary, Alberta, Canada}, abstract = {In the Chihuahuan Desert concern about both the loss of biodiversity and economic productivity centers on the loss of grasslands and their transition to shrublands (i.e., desertification). Decades of research on this process have emphasized relatively fine scales. Although this was a necessary step, alone it is insufficient to explain instances and broader patterns of change. Furthermore, these processes have been only tenuously linked to biodiversity. We describe recent conceptual and empirical approaches to describing the process of transition based on cross-scale interactions between grass-shrub relationships and losses of grass in patches, between-patch connectivity and interactions with climate forcing functions, and landscape to regional-level feedbacks to climate. These processes create nonlinear changes in time and space such that different processes are important at particular times and spatial locations. This notion has important implications for monitoring and management. The variety of dynamics and patterns in vegetation and soils these processes create drive spatial and temporal variation in biodiversity. We discuss ongoing work to link ecosystem models to biodiversity data and to integrate management strategies based on rangeland and wildlife concerns.}, keywords = {approaches, biodiversity, Chihuahuan Desert, cross-scale}, author = {Brandon T Bestelmeyer and Debra C. Peters and Kris Havstad} } @conference {50632, title = {Soil-geomorphic basis of divergent landscape trajectories in the Chihuahuan Desert}, booktitle = {89th Annual Meeting, Ecological Society of America}, year = {2004}, month = {August 1, 2004}, pages = {p. 45}, address = {Portland, OR}, abstract = {A major emphasis of rangeland ecology and management is to understand the factors that regulate rates of vegetation and soil change. Explanations of change have traditionally ignored subtle soil heterogeneity and emphasized single processes. We sought to employ a multiscale, multifactor framework to interpret variability in rates of vegetation change occurring within a Chihuahuan Desert grassland under similar management. We used a combination of ground-based measures and remote-sensed data from 1936 and 1996 to construct a scenario explaining different rates of grass loss in two adjacent grassland areas on a piedmont slope. The two areas now merge at sharp ecotone separating a high-grass, low-shrub cover state and a state with lowgrass, high-shrub, and high-bare ground cover. The basis for these divergent trajectories is related to differences in the spatial pattern of soil calcium carbonate content and argillic horizon development. Where high carbonate soils with weak argillic horizons are relatively continuous, single-crown and stoloniferous grasses dominate at the expense of a rhizomatous grass. Grazing appears to have contributed to higher connectivity of bare ground where single-crown grasses predominated, leading to increased susceptibility to erosion, lower soil aggregate stability, lower rainfall infiltration, and soil truncation leading to accelerated rates of grass and shrub mortality. Under these conditions, grass and shrub cover are positively correlated at fine scales even when they are negatively correlated at a broad scale. Eroded soil accumulates on the highgrass side of the ecotone, contributing to ecotone contrast. This example illustrates the need for multiscale perspectives in explaining ecosystem resistance and resilience.}, keywords = {Chihuahuan Desert, ecology, management, rangeland, vegetation and soil change}, author = {Brandon T Bestelmeyer and J.P. Ward and Jeffrey E. Herrick and A.J. Tugel} } @article {50644, title = {Modeling the reflectance anisotropy of Chihuahuan Desert grass-shrub transition canopy-soil complexes}, journal = {International Journal of Remote Sensing}, volume = {25}, number = {14}, year = {2004}, month = {2004}, pages = {2725-2745}, abstract = {The goal of the research presented is to understand better the factors controlling the remotely sensed signal returned in the red wavelengths from grass-shrub transition canopy-soil complexes. The specific objectives were to evaluate the importance of the different elements (overstory, understory, soil) in the bi-directional reflectance distribution function (BRDF) and to explore the behavior of simple parametric and explicit scattering models with respect to observations. The first objective was approached by simulations using the Radiosity Graphics Method (RGM) with surface parameters provided by measurements of plant locations and dimensions surveyed over 25m plots. The second was approached through simulations of bi-directional reflectance by both the RGM and a Simplified Geometric Model (SGM). The simulated reflectance values were assessed against samples of the BRDF at a wavelength of 650nm acquired from the air at six view zenith angles and three solar zenith angles by a tilting, radiometrically-calibrated multispectral digital camera providing multi-angle observations (MAO). The results show that the understory of small forbs and sub-shrubs plays a very important role in determining the brightness and to some extent reflectance anisotropy of these landscapes. This is owing to the potential large number density of broom snakeweed and to a varying proportion of black grama grass and prone grass litter. Both of these components darken the scene. The SGM performed well measured against both the RGM and the MAO (r2 of 0.98 and 0.92 against the RGM and MAO, respectively). Both models underestimated reflectance by a small amount, less than 6\% over all angles, with both showing increasing divergence from the backcsattering into the forward-scattering direction.}, keywords = {BRDF, canopy-soil complexes, Chihuahuan Desert, grass-shrub transition, reflectance anisotropy, remote sensing, RGM, SGM}, url = {/files/bibliography/04-005.pdf}, author = {M. Chopping and L. Su and A. Rango and Connie J. Maxwell} } @conference {50648, title = {The role of heteromyid rodents in establishment and survival of mesquite in Chihuahuan Desert black grama (Bouteloua eriopoda) grasslands}, booktitle = {Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region}, year = {2004}, month = {October 15, 2004}, pages = {21}, address = {Alpine, TX}, abstract = {We conducted experiments to examine the relative influence of fire, small mammal activity, and microsite location on the germination and survival of honey mesquite (Prosopis glandulosa) in Chihuahuan Desert black grama (Bouteloua eriopoda) grassland. Mesquite seeds were placed in simulated heteromyid rodent cache pits in unburned and burned black grama grassland and on banner-tailed kangaroo rat (Dipodomys spectabilis) burrow mounds. Germination was highest in the unburned grassland, but over-winter survival was greater in the burn microsites. A large proportion seed pits were partially excavated (between 15.6 to 21.1\% of the uncaged pits and between 1.1 to 5.5\% of the caged pits). However, between 0 to 50.0\% of the seedlings germinated in pits that had previously been excavated. Of the seeds placed in the field in the early monsoon season, 8.0\% survived over winter and 13.6\% of the germinants from the post-monsoon season survived over winter. There was higher germination (13.8\%) from the early monsoon experiment than in the post-monsoon experiment (3.9\%). There were seasonal differences in numbers of emergent seedlings with a peak in September 2002 following late summer rains. There were no significant differences in numbers of germinants in burn and grass microsites, but there were significantly fewer germinants on banner-tailed kangaroo rat mounds. These studies suggest that heteromyid rodents may serve as agents of dispersal for honey mesquite in Chihuahuan Desert black grama grasslands.}, keywords = {agents of dispersal, black grama, Chihuahuan Desert, fire, heteromyid rodents, mesquite, microsite location, small mammal activity}, author = {B.D. Duval and Aaron Killgore and E. Jackson and Walter G. Whitford} } @conference {50653, title = {Mesquite recruitment: historic patterns with long-term impacts}, booktitle = {Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region}, year = {2004}, month = {October 15, 2004}, pages = {24}, address = {Alpine, TX}, abstract = {Mesquite (Prosopis glandulosa Torrey) has increased in dominance over large areas of the Chihuahuan Desert, chiefly at the expense of once expansive desert grasslands. Excessive grazing and seed dissemination by livestock are often attributed as the cause of this transition. We propose an alternate hypothesis that expansion of mesquite is not due to simple cause and effect relationships, but rather a network of cause and effect relationships. We assert that mesquite expansion may have occurred even in the absence of the widespread livestock grazing occurring during the last 130 years. We then look at factors that attenuate or intensify mesquite expansion and how a series of small-scale but temporally seminal events propagate across multiple scales. Lastly, we examine how acceptance of this hypothesis, or its parts, might be useful in enhancing 21st century efforts focused on remediation of desert grasslands.}, keywords = {Chihuahuan Desert, excessive grazing, long-term impacts, mesquite, patterns, seed dissemination, small-scale events}, author = {E.L. Fredrickson and Laurie Abbott and D.M. Anderson and Richard E. Estell} } @article {50656, title = {Sand flux in the northern Chihuahuan desert, New Mexico, USA, and the influence of mesquite-dominated landscapes}, journal = {Journal of Geophysical Research}, volume = {109}, number = {F04003, doi:10.J029/2003JF000031}, year = {2004}, month = {2004}, abstract = {

Measurements of sand flux over areas with different vegetation in the Chihuahuan desert show that mean, height-integrated, horizontal flux values for mesquite-dominated sites were higher than those for other kinds of vegetation. Sand transport over mesquite areas displayed seasonal variability for most years. This seasonal variability roughly followed the variability of strong winds. Sand transport rates for collectors within a short distance downwind of mesquite bushes were small compared to those for collectors at the end of streets (elongated patches of bare soil) aligned with wind direction. The increased rate of sand transport (wind erosion) associated with mesquite is important because mesquite-dominated areas are increasing in the northern Chihuahuan desert and are therefore responsible for increasing land degradation (desertification).

}, keywords = {Chihuahuan Desert, desert vegetation, dust emissions, journal article, mesquite, sand flux, sand transport}, doi = {10.1029/2003JF000031}, url = {/files/bibliography/04-010.pdf}, author = {D. E. Gillette and Pitchford, A.M.} } @conference {50676, title = {Fire in Chihuahuan Desert grassland: effects on vegetation, small mammal populations, and biopedoturbation}, booktitle = {Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region}, year = {2004}, month = {October 15, 2004}, pages = {30}, address = {Alpine, TX}, abstract = {We studied the effect of a prescribed burn in a black-grama-(Bouteloua eriopoda)-dominated desert grassland on vegetation, small mammals and biopedoturbation (soil disturbance by animals). The burn was conducted during the hot-dry season just prior to monsoon rains. One month post-burn, there were significant decreases in canopy cover of the grasses (Bouteloua eriopoda, Sporobolusflexuosus, and Aristida purpurea). One year post-burn, percent cover of B. eriopoda remained significantly lower than in unburned areas. There were no differences in cover of all other grass species in burned and unburned plots 1 year after the burn. Fire killed 100\% of the snakeweed shrubs (Gutierrezia sarothrae), 77\% of the Torrey ephedra (Ephedra torreyana), and 36\% of the soap tree yucca (Yucca elata). One year post-burn, the surviving Y. elata were significantly smaller than the soap tree yucca in the unburned sites. The fire resulted in top kill of all P. glandulosa in the burn areas but all of the mesquite resprouted from root crowns within 1 month after the burn. Fire had no effect on the abundance and diversity of small mammals. Area and volume of soil disturbed by animals (ant nest soil mounds, burrowing spider tunnels and ejected soil, and excavations by small mammals) were not significantly different in burned areas and unburned areas. The area and volume of soil in termite galleries and sheeting were significantly larger in the unburned grassland than in the burned areas.}, keywords = {biopedoturbation, Chihuahuan Desert, effects, fire, grassland, small mammal populations, vegetation}, author = {Aaron Killgore and E. Jackson and Walter G. Whitford} } @conference {50686, title = {Spatial variation in remnant black grama plants in a creosote-dominated bajada}, booktitle = {Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region}, year = {2004}, month = {October 15, 2004}, pages = {33}, address = {Alpine, TX}, abstract = {Much of the Chihuahuan Desert has converted from perennial grasslands to shrub-dominated systems over the past century. Although shrub-dominated systems appear homogeneous with very few grass plants, observations suggest that perennial grasses can occur within these areas. Our overall objective was to quantify the presence and abundance of the perennial grass, Bouteloua eriopoda (black grama), in creosotebush-dominated bajadas at the Jornada Experimental Range in southern New Mexico. In 2002 and 2003, we obtained the geo-referenced location, aspect, two diameters, and location within shrub canopies for all black grama plants in a 530 m x 550 m area located inside and outside an exclosure constructed in the 1930s. Spatial data layers in a GIS were used as explanatory variables in our analyses. Our results show that a total of 3335 black grama plants were found with an average density of 0.01 plants/m2. Most black grama plants were found inside and adjacent to arroyos (66.7\%), at a northern aspect (47\%), and outside the exclosure (62\%). Black grama most likely dominated this site in 1858, although by 1915 the area was dominated by tarbush, and by 1998 it was dominated by creosote. Thus, the source population for these current black grama plants is most likely remnant plants that historically dominated the area, although seed inputs from nearby mountainous pastures are also possible. Our results showing the location of black grama plants within creosote-dominated systems can be used for remediation of these areas.}, keywords = {black grama, Bouteloua eriopoda, Chihuahuan Desert, creosote-dominated bajada, remediation, spatial variation}, author = {Mariotto, I. and Debra C. Peters and Kris Havstad and L. W. Murray} } @conference {50689, title = {Broad-scale landscape, soil, and wind influences on fine-scale dynamics}, booktitle = {Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region}, year = {2004}, month = {October 15, 2004}, pages = {35}, address = {Alpine, TX}, abstract = {Desertification and other ecogeomorphic changes in the Chihuahuan Desert are connected to broad-scale landscape, soil, and wind drivers via fine-scale processes. Landscapes function as a driver by their lithic composition and topographic configuration. These impact water redistribution and wind movement across the landscape that influence soil patterns at the landscape scale. Strong winds in the Jornada Basin, for example, have decapitated sandy soils, formed erosional streets, pushed sand grains up the piedmont slope and over ridges into intermountain valleys where they have accumulated as thick, eolian deposits overlying bedrock. Fine-scale processes are influenced by these broad-scale drivers in several ways. Wind erosion, for instance, removes organic matter and coarsens soil texture, thereby lowering water-holding capacity, cation exchange capacity, and nutrient availability. Because such fine-scale processes exert important controls on plants, vegetation patterns at the landscape scale reflect patterns of the broad-scale drivers. Consequently, some ecogeomorphic conditions, such as black grama on sandy, eolian upland soils, are more prone to desertification than other conditions, like tobosa grass on silty, alluvial soils in run-in positions.}, keywords = {broad-scale, Chihuahuan Desert, desertification, ecogeomorphic, fine-scale dynamics, landscape, soil, wind}, author = {Curtis H. Monger and D. E. Gillette and Brandon T Bestelmeyer} } @conference {50701, title = {Nonlinear dynamics in arid systems: interactions among drivers and processes across scales}, booktitle = {Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region}, year = {2004}, month = {October 15, 2004}, pages = {38}, address = {Alpine, TX}, abstract = {Conversion from perennial grasslands to shrub-dominated systems has occurred globally in arid and semiarid systems and regionally in the Chihuahuan Desert over the past 100-150 years. Broad-scale drivers, such as grazing and extreme drought, are often invoked to explain shrub invasion dynamics. We use long-term, spatially explicit data to show that these drivers are frequently insufficient to explain patterns in shrub invasion and grass persistence at the landscape scale. At the Jornada Experimental Range, we are developing a new conceptual framework to explain high temporal and spatial variation in landscape patterns and dynamics. Our framework focuses on five key aspects of these systems: (1) threshold behavior, (2) spatially contagious processes, (3) landscape context, (4) feedbacks between biotic and abiotic processes at multiple scales, and (5) landscape legacies. We show how accounting for these key aspects of system behavior can explain nonlinear dynamics across spatial and temporal scales. This talk provides the background for the remaining talks in the special session {\textquotedblleft}Landscape linkages and cross-scale interactions in the Chihuahuan Desert.{\textquotedblright}}, keywords = {arid systems, broad-scale drivers, Chihuahuan Desert, drivers, feedbacks, interactions, landscape contest, nonlinear dynamics, processes, scales, spatially contagious processes, threshold behavior}, author = {Debra C. Peters and Kris Havstad} } @conference {50717, title = {Temporal variation in water availability}, booktitle = {Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region}, year = {2004}, month = {October 15, 2004}, pages = {42}, address = {Alpine, TX}, abstract = {Desert regions in the southwestern United States and northern Mexico exhibit a high degree of temporal variability in water availability. This temporal variability is a result of shifting climate regimes over centuries and decades, interannual variation in weather patterns, seasonal differences n the nature of winter and summer precipitation, within-season variability of precipitation frequency and magnitude, soil textural properties, differences in vegetation structure, and soil water. Pulses of rainfall during the summer growing season are highly unpredictable and punctuated by intervening dry periods of variable lengths. These dry periods are frequently severe enough to limit biotic activity and modify abiotic processes. Therefore, within a landscape type the relationship between aboveground net primary productivity and annual rainfall lacks predictive power due to the pulse-driven nature of these systems. In the Chihuahuan Desert encroachment of C3 shrub species into areas formerly dominated by C4 grasses appears to interact with water variability and create positive feedbacks that facilitate further shrub encroachment and loss of grass cover. In order to understand these systems, we need to develop knowledge of how temporal patterns in water availability affect ecosystem water use, nutrient availability, productivity, and species composition. Data from rainfall manipulation experiments, Bowen-Ration towers, and long-term soil moisture illustrate that mesquite shrubs respond to both small and large rainfall events, respiratory losses of carbon dioxide often offset photosynthetic uptake of carbon dioxide, and the capacity for carbon sequestration during summer months is largely driven by rainfall patterns.}, keywords = {Chihuahuan Desert, pulse-driven nature, shifting climate regimes, temporal variation, water availability, weather patterns}, author = {K. A. Snyder and S. Tartowski and V. P. Gutschick} } @article {50730, title = {Pairwise species associations in the perennial vegetation of the northern Chihuahuan Desert}, journal = {The Southwestern Naturalist}, volume = {49}, number = {1}, year = {2004}, month = {March 1, 2004}, pages = {1-10}, abstract = {We analyzed pairwise species associations based on presence/absence data from transects of perennial vegetation at 129 sites located in the northern Chihuahuan Desert. The sites were chosen to represent the range of commonly encountered desert vegetation types from grassland to shrubland. Twenty-four significant associations were found, all of which were positive (i.e., the species pairs co-occurred more frequently than would be expected by chance). Some of the species associations identified by our analysis have been noted in the literature previously but others have not and warrant further investigation. Given the nature and scale of the data used in our analysis, the associations we uncovered most likely represent species with similarities in ecological requirements or tolerances but might or might not indicate strong interaction at the scale of individual plants.}, keywords = {Chihuahuan Desert, pairwise species, perennial vegetation}, url = {/files/bibliography/04-077.pdf}, author = {S.J. Turner and A. R. Johnson and Walter G. Whitford} } @article {50749, title = {Applying species diversity theory to land management}, journal = {Ecological Applications}, volume = {13}, number = {6}, year = {2003}, month = {December 1, 2003}, pages = {1750-1761}, abstract = {

Many theories and hypotheses have been proposed to explain patterns of species diversity and distribution/abundance at particular scales, but they are often unclear on how these ideas relate or how they apply across multiple scales. It has been difficult to use diversity theory to understand patterns at the intermediate scales at which biodiversity is managed. Here, we present a framework for studying diversity based on the ecological processes influencing distribution of organisms at different scales. We use this framework to organize diversity theories into several classes. The framework highlights that processes contributing to diversity patterns depend on the characteristics of the taxa considered, the spatial scales at which organisms respond to environment, and the scales and other characteristics of the particular environments in which investigators hope to explain variation in diversity. At the scales traditionally considered by land managers and conservation biologists, biodiversity is determined b the interactions among habitat occupancy, landscape distribution, and geographic range for a variety of taxa. The framework suggests that, in each case, managers should address the following general questions: 1) which groups of organisms will be considered, 2) how do their domains of scale relate to the land area under consideration, 3) what processes are likely to be important determinants of species distribution at management scales, and 4) how will the proposed management activities interact with these processes? We emphasize the value of considering species diversity theories in a pluralistic and case-specific way, rather than seeking singular explanations or "general laws" explaining diversity variations.

}, keywords = {Chihuahuan Desert, competition, conservation, dispersal, land management, landscape ecology, limitation geographic, macroecology, natural resources management, range habitat, Selection, species diversity}, doi = {10.1890/02-5089}, url = {files/bibliography/JRN00376.pdf}, author = {Brandon T Bestelmeyer and J.R. Miller and J.A. Wiens} } @article {50789, title = {Desertification and biopedturbation in the northern Chihuahuan Desert}, journal = {Journal of Arid Environments}, volume = {53}, number = {1}, year = {2003}, month = {January 1, 2003}, pages = {1-14}, abstract = {

We examined the relationship between biopedturbation (animal-caused soil disturbance) and several vegetation and soil-based indicators of rangeland condition to evaluate the effects of desertification on animal soil disturbance. The area, volume, and abundance of various biopedturbation types were assessed at 117 sites in south-central New Mexico where vegetative cover and composition had previously been measured. There were significant relationships between biopedturbation and selected rangeland condition indicators. Increasing percentages of grass cover were positively associated with increasing total area of biopedturbation. Increasing percentages of shrub cover and mean bare patch size were negatively associated with total biopedturbation area. Biopedturbation area and volume were related to indicators of rangeland condition and percent shrub cover best predicts the area of soil disturbed by animals. This relationship, however, cannot reliably predict total biopedturbation area or the area of soil disturbance types.

}, keywords = {Biopedturbation, Chihuahuan Desert, condition indicators, desertification, disturbance, rangeland, soil}, doi = {10.1006/jare.2002.1022}, url = {/files/bibliography/03-009.pdf}, author = {E. Jackson and Krogh, S.N. and Walter G. Whitford} } @article {50819, title = {Investigating landscape instability in the northern Chihuahuan Desert at multiple scales using 137 Cesium}, journal = {Journal of Arid Environments}, volume = {55}, year = {2003}, note = {//?//LTER IV//}, month = {2003}, pages = {737-746}, keywords = {article, articles, Chihuahuan Desert, instability, landscape, isotopes, 137Cesium, journal, journals, landscape, evolution, landscape, instability}, author = {Jerry Ritchie and Jeffrey E. Herrick and Ritchie, C.A.} } @article {50900, title = {Presence/absence of a keystone species as an indicator of rangeland health}, journal = {Journal of Arid Environments}, volume = {50}, number = {3}, year = {2002}, month = {March 1, 2002}, pages = {513-519}, abstract = {

We examined the relationship between a Chihuahuan Desert grassland keystone species (banner-tailed kangaroo rat, Dipodomys spectabilis) and several vegetation and soil indicators of rangeland health in order to define a threshold indicator value for irreversible change in ecosystem structure and function. The abundance of occupied and/or abandoned D. spectabilis burrow-mounds was assessed at 117 sites in south central New Mexico where previous studies had reported vegetation cover and composition. The most robust indicator for presence/absence of D. spectabilis was shrub cover. D. spectabilis did not occur at sites with shrub cover greater than 20\%. It was concluded that a threshold value of 20\% shrub cover could be applied to assessment and monitoring of Chihuahuan Desert rangelands because higher shrub cover results in the local extinction of this keystone species. The combination of data on the presence/absence of a keystone species with vegetation and soil indicators provides a method for identifying thresholds of degradation that may be irreversible.

}, keywords = {banner-tailed kangaroo rat, Chihuahuan Desert, degradation threshold, desertification, Dipodomys spectabilis, environmental indicators}, doi = {10.1006/jare.2001.0900}, url = {files/bibliography/02-JAE-Whitford.pdf}, author = {Krogh, S.N. and Zeisset, M.S. and E. Jackson and Walter G. Whitford} } @article {50926, title = {Plant species dominance at a grassland-shrubland ecotone: An individual-based gap dynamics model of herbaceous and woody species}, journal = {Ecological Modelling}, volume = {152}, number = {1}, year = {2002}, month = {June 1, 2002}, pages = {5-32}, abstract = {

Transition zones or ecotones between biomes are predicted to be particularly sensitive areas to directional changes in climate. However, for many ecotones, there is little understanding of the key processes that allow dominant species from adjacent biomes to coexist at transition zones and how differences in these processes affect species responses to changes in environmental conditions. The objective of this study was to examine the relationship between plant life history traits and patterns in dominance and composition at a grassland{\textendash}shrubland transition zone in order to predict shifts in dominance with directional changes in climate. It was hypothesized that differences in life history traits allow species from adjacent biomes to coexist at this transition zone, and that these dominance patterns are dynamic through time as a result of species-specific responses to changes in climate. A mixed lifeform individual plant-based gap dynamics model (ECOTONE) was developed to examine consequences of differences in recruitment, resource acquisition, and mortality to patterns in species dominance and composition under a variety of soils and climatic conditions. This model is unique because it represents interactions among multiple potential dominant species that include congeneric species of one lifeform as well as herbaceous and woody lifeforms across multiple spatial scales. Similar to other gap models, ECOTONE simulates the recruitment, growth, and mortality of individual plants on a small plot through time at an annual timestep. ECOTONE differs from other gap models in the degree of detail involved in determining successful recruitment by each species and in the simulation of belowground resources. Individual plant root distributions and resource availability by depth are dynamic. Soil water content is simulated on a daily timestep and nitrogen is simulated monthly. Multiple spatial scales can be simulated using a grid of plots connected by seed dispersal. ECOTONE was parameterized for two soil types at the Sevilleta National Wildlife Refuge (SEV), a site located within the transition zone between two major biomes in North America. Shortgrass steppe communities are dominated by the perennial grass Bouteloua gracilis (blue grama) and Chihuahuan desert communities are dominated by the perennial grass Bouteloua eriopoda (black grama) or the shrub Larrea tridentata (creosotebush). Experiments were conducted to provide key parameters related to recruitment and growth that were supplemented with information from the literature for remaining parameters. Model output was verified using field estimates of cover and biomass for the three dominant species as well as other groups of species. Simulation analyses were conducted under current climate and for a directional change in climate. Nitrogen was assumed constant for all runs to allow a focus on water availability constraints as affected by climate. Under current climatic conditions, simulated biomass on sandy loam soils was dominated by B. eriopoda with smaller biomass of B. gracilis and other species groups. By contrast, simulated biomass on a loamy sand soil was codominated by B. eriopoda and L. tridentata with very small biomass attributed to other species groups. Under a GFDL climate change scenario of increased year-round temperatures and increased summer precipitation, vegetation patterns shifted to a clear dominance of biomass by B. eriopoda on both soil types. These results show that temporal partitioning of soil water is important to codominance by the two Bouteloua species, and that spatial and temporal partitioning of soil water is important for grass{\textendash}shrub interactions. The results also suggest that global climate change may provide a mechanism for the recovery of B. eriopoda following shrub invasion in the Southwestern U.S. Thus, an individual-based modeling approach is capable of representing complex interactions among herbaceous and woody species as well as between congeneric species with different life history traits at a biome transition zone. This modeling approach is useful in improving our understanding of key processes driving these vegetation dynamics as well in predicting shifts in dominance as environmental conditions change in the future.

}, keywords = {Bouteloua species, Chihuahuan Desert, climate change, creosotebush, ECOTONE, shortgrass steppe}, doi = {10.1016/S0304-3800(01)00460-4}, url = {files/bibliography/JRN00362.pdf}, author = {Debra C. Peters} } @proceedings {50982, title = {Fire, grazing and honey mesquite invasion in black grama-dominated grasslands of the Chihuahuan Desert: a synthesis}, year = {2001}, month = {November 28-Dece}, pages = {31-39}, address = {Tallahassee, FL}, abstract = {Prior to European settlement, the Chihuahuan Desert was partly comprised of grasslands dominated by the perennial grass, black grama (Bouteloua eriopoda), as well as by other species of herbaceous vegetation. Honey mesquite (Prosopis glandulosa) was mostly abundant in adjacent lower lying areas of water runoff and intermittent streambeds. Since the late 19th century, however, cattle have been directly responsible for increased abundances and expanded distributions of honey mesquite through consumption and dissemination of seed. Additionally, a period of overgrazing and interactive effects with other factors, such as drought and small mammal herbivory, resulted in reduced abundances of black grama. As a result of decreased fuel abundance, lightning-initiated fires that likely occurred just prior and throughout the growing season have decreased in size, intensity, and frequency. Despite reductions in herbaceous fuels following gEuropean settlement, we hypothesize that fire remains effective in topkilling shrubs of honey mesquite and, in so doing, may directly interfere with its development toward reproductive maturity and its ability to set seed. Based on information from the literature and results from our research, complete kill of honey mesquite is rare. However, fire is effective in topkilling and returning shrubs to an immature life history stage. Fire remains an effective deterrent in slowing honey mesquite invasion. However, the recurrence of fire is highly contingent on the degree and rate of black grama recovery that may be determined by the timing and amount of precipitation immediately following fires, as well as the degree of livestock grazing.}, keywords = {Chihuahuan Desert, fire, grazing, honey mesquite, invasion}, url = {/files/bibliography/01-020.pdf}, author = {Drewa, P.B. and Debra C. Peters and Kris Havstad} } @article {50988, title = {Root systems of some Chihuahuan Desert plants}, journal = {Journal of Arid Environments}, volume = {49}, number = {2}, year = {2001}, month = {October 1, 2001}, pages = {221-263}, abstract = {Root systems of 11 shrub or shrub-like species, 11 grass species, 19 perennial forb species and 4 annual forb species were excavated on the Jornada Experimental Range in the northern Chihuahuan Desert in southern New Mexico, USA. Maximum radial horizontal spread of shrub root systems usually occurred above calcic and petrocalcic horizons at depths above 1 m. .With one exception, all shrub species roots were traced through calcic and petrocalcic horizons to depths down to 5 m. Upward growing roots reaching very shallow depths (\< 10 cm) were common for most shrub species. Thus, the shrubs can readily access soil water and nutrients from both surface and deep soil horizons. Grass root systems on sandy soils extended radially up to 1.4 m, perhaps an adaptation to capture more soil water from the frequent small rainfall events. Grass roots did not extend through calcic or petrocalcic horizons and none penetrated deeper than 1.6 m. Perennial forb root systems varied in depth of branching but often penetrated into o through calcic and petrocalcic horizons and, like shrubs, have an advantage over grasses during droughts. Root systems of the annual forbs, excavated at the end of a season of above average precipitation, reached depths of 0.5 to 1.2 m. At each of the 18 excavation sites the roots of all the plant life forms were highly intermingled in the upper soil horizons, indicating that competition for water and soil nutrients is intense. It is believed that the plasticity and architecture of the shrub root systems, enabling them to compete with the grasses for soil water in the upper soil horizons and also access soil water at depths beyond the reach of grass roots, has been a major reason for the increase of shrubs during the historical period in this arid environment.}, keywords = {Chihuahuan Desert, competition, forbs, grasses, Jornada, root systems, shrubs, soil resources}, doi = {10.1006/jare.2000.0784}, url = {/files/bibliography/01-023.pdf}, author = {Gibbens, Robert P. and J.M. Lenz} } @article {51015, title = {Detecting fragmentation of cover in desert grasslands using line intercept}, journal = {Journal of Range Management}, volume = {54}, number = {1}, year = {2001}, month = {January 1, 2001}, pages = {61-66}, abstract = {We examined the relationship between a Chihuahuan Desert grassland keystone species (banner-tailed kangaroo rat, Dipodomys spectabilis) and several vegetation and soil indicators of rangeland health in order to define a threshold indicator value for irreversible change in ecosystem structure and function. The abundance of occupied and/or abandoned D. spectabilis burrow-mounds was assessed at 117 sites in south central New Mexico where previous studies had reported vegetation cover and composition. The most robust indicator for presence/absence of D. spectabilis was shrub cover. D. spectabilis did not occur at sites with shrub cover greater than 20\%. It was concluded that a threshold value of 20\% shrub cover could be applied to assessment and monitoring of Chihuahuan Desert rangelands because higher shrub cover results in the local extinction of this keystone species. The combination of data on the presence/absence of a keystone species with vegetation and soil indicators provides a method for identifying thresholds of degradation that may be irreversible.}, keywords = {Chihuahuan Desert, grassland, indicators, keystone species, rangeland health, shrub cover}, url = {http://jrm.library.arizona.edu/jrm/GetFileServlet?file=file:///data1/pdf/TheJournalOfRangeManagement/Volume54/Number1/azu_jrm_v54_n1_61_66_m.pdf\&type=application/pdf}, author = {Kuehl, R.O. and M.P. McClaran and Justin Van Zee} } @article {51058, title = {Persistence of biosolids in a Chihuahuan Desert rangeland 18 years after application}, journal = {Arid Land Research and Management}, volume = {15}, year = {2001}, note = {//?//LTER IV//}, month = {2001}, pages = {223-232}, abstract = {

The experimental application of municipal biosolids to degraded arid and semiarid rangelands has been practiced for many years and is becoming more common in the western United States. Previous studies have examined the effects of applying biosolids to land areas that have been degraded by one or more different factors including overgrazing, fire suppression, and increased drought frequency, duration, or intensity. However,few of these studies have measured the persistence of biosolids in the soil. This study is an attempt to recover information from an abandoned reclamation effort in which municipal biosolids were spread on a degraded rangeland on the Jornada Experimental Range in southern New Mexico. The biosolids were applied in 1979 and were still present in substantial amounts when soil samples were taken in 1997. An estimated 32\% of the applied biosolids persisted as fragments greater than 2 mm in diameter for almost 20 years. There were no apparent benefits of biosolid application at this site in terms of vegetation establishment within the first four years, and there was no correlation between vegetation patterns and the concentration of biosolids remaining in the soil in 1997. It is hypothesized that much of the applied sludge remains in the soil because of the recalcitrant nature of digested biosolids combined with the environmental conditions of soil in and systems. Long-term? results from biosolid addition experiments in and and semiarid rangelands should be considered before the practice is widely, used for reclamation of degraded rangeland sites.

}, keywords = {article, articles, biosolids, Chihuahuan Desert, journal, journals}, doi = {10.1080/15324980152119784 }, url = {files/bibliography/JRN00342_0.pdf}, author = {Walton, M. and Jeffrey E. Herrick and Gibbens, Robert P. and M.D. Remmenga} } @article {51061, title = {Establishment and effects of establishment of creosotebush, Larrea tridentata, on a Chihuahuan Desert watershed}, journal = {Journal of Arid Environments}, volume = {47}, number = {1}, year = {2001}, month = {January 1, 2001}, pages = {1-10}, abstract = {Creosotebush (Larrea tridentata) seedlings were planted in plots that were irrigated, plots that were irrigated and fertilized with ammonium nitrate, and plots that were not amended in three plant communities on a Chihuahuan Desert watershed: ungrazed black grama (Bouteloua eriopoda) grassland, creosotebush shrubland, and overgrazed grassland. No seedlings were planted in one-half of the area of each plot. No seedlings survived in the black grama grassland or the creosotebush shrubland 2 years after planting. Growth of established creosotebush shrubs was highest in plots with the lowest grass cover. Fifteen years after the seedlings were planted in the overgrazed grassland, the area under the shrubs was nearly devoid of perennial grasses and forbs. The aggregate stability of the soils under the established creosotebush shrubs was significantly lower than the soils in the unplanted split-half of the plots. Electrical conductivity, calcium, and nitrate were significantly lower in soils under shrubs than soils in the unplanted split-half of the plots. There were also significant reductions in densities of annual plants growing under the shrubs than in the unplanted split-half of the plots. Successful establishment of creosotebush in desert grasslands is dependent upon the presence of large patches of soil with no perennial plant cover. Intense grazing by domestic livestock creates microsites and landscape characteristics favorable for seed dispersal, germination and establishment of creosotebush. Soil changes resulting from shrub establishment reduce the probability of reestablishing perennial grasses in creosotebush-dominated shrubland.}, keywords = {Chihuahuan Desert, creosotebush, effects, establishment, Larrea tridentata}, url = {/files/bibliography/01-057.pdf}, author = {Walter G. Whitford and R. M. Nielson and A.G. de Soyza} } @proceedings {51122, title = {Soil surface indicators of desertification from the northern Chihuahuan Desert and the Great Basin}, volume = {1}, year = {2000}, month = {July 19-23, 1999}, pages = {137}, address = {Townsville, Australia}, abstract = {We measured vegetation canopy and litter cover in ungrazed exclosures and adjacent pastures at three locations in the Chihuahuan Desert, five locations near Burns, Oregon, seven locations near Milford, Utah, and six near Idaho Falls, Idaho, all of which are in the Great Basin. We found that vegetation cover is not a good surrogate for estimating litter cover. Refinements that take into account vegetation species composition may improve the ability to predict litter cover from vegetation data.}, keywords = {Chihuahuan Desert, desertification, Great Basin, indicators, soil surface}, url = {/files/bibliography/00-002.pdf}, author = {A.G. de Soyza and Walter G. Whitford and Justin Van Zee and Jeffrey E. Herrick and Kris Havstad} } @proceedings {51066, title = {Rangeland research in the Chihuahuan Desert}, year = {2000}, month = {03/2000}, pages = {80-81}, abstract = {

The mission of the Jornada Experimental Range is to develop new technologies for the management and remediation of desert rangelands. We are developing a manual for monitoring rangeland health. Several indicators have been examined and a number of these indicators have proven useful for monitoring purposes, e.g., size of unvegetated patch, perennial grass cover rand soil surface stability. We have worked with individual ranchers in New Mexico to test these methods and have established pilot projects on state lands to demonstrate their application to management. We are also studying prescribed burning of arid rangeland as a tool to improve degraded rangelands. The fire treatment was applied to study sites in 1999 and initial responses to fire and grazing effects will be measured in 2000. We will evaluate effects of fire on ecological processes and post-fire grazing and identify post-fire guidelines for recovery of key species in grazed Chihuahuan Desert grassland. One of our major research objectives is to develop new technologies for controlling distribution of livestock grazing rangelands. Few options presently exist for monitoring animal location and controlling animal movement to a specific area at a particular time. A method and apparatus have been developed that may allow for management of grazing livestock without ground-based fencing. The device worn by an animal incorporates a global positioning system and a geographic information system database to determine and control individual animal movements. We are field testing the ability of a third generation prototype to contain an animal in an area using bilaterally applied sensory cues. This technology could allow producers to reduce management costs, improve utilization of forage and protect ecologically sensitive areas.

}, keywords = {cattle growers, Chihuahuan Desert, livestock, rangeland research, research notes}, url = {/files/bibliography/562.pdf}, author = {Richard E. Estell and D.M. Anderson and J.R. Barrow and E.L. Fredrickson and Kris Havstad and Jeffrey E. Herrick and Debra C. Peters} } @conference {51084, title = {Effects of shrubs and disturbances on pattern and process in Chihuahuan Desert grasslands}, booktitle = {85th Annual Meeting, Ecological Society of America}, year = {2000}, month = {August 6, 2000}, pages = {393}, address = {Snowbird, UT}, abstract = {

Disturbances can cause patchiness in the vegetation at different spatial and temporal scales. In arid environments, dominant species of the vegetation are similar to disturbances in that they create patches with a modified biotic and abiotic environment. Shrub invasion in arid environments has caused a shift in the dominant life form, which is expected to have important implications for the occurrence of subdominant plants. The objective of this study was to understand and predict changes in the relative abundance of subdominant species when an evergreen shrub (Larrea tridentata) invades desert grasslands dominated by Bouteloua eriopoda, and to compare those changes to other disturbances that affect the vegetation. We used a spatially-explicit individual-plant based model (ECOTONE) to simulate responses of desert grassland species to shrub invasion using a hierarchical patch dynamics approach. The effects of changes in light, water, and nutrients caused either by disturbance or shrub invasion on subdominant species were evaluated. We found that the effects of shrub invasion on species composition were comparable to other disturbances. However, contrary to other disturbances, changes in processes induced by shrub invasion appear to be self-reinforcing, whereas species recover after disturbances. As a consequence, initially positive effects of shading by shrubs on the abundance of subdominant species ultimately caused a loss of subdominant plants as shrub cover increased. These results correspond to field data collected at a desert grassland-shrubland ecotone at the Sevilleta LTER in New Mexico. Our study demonstrates the similarity and differences of invasive species to disturbances.

}, keywords = {Chihuahuan Desert, disturbances, grasslands, Sevilleta LTER, shrub invasion}, author = {Hochstrasser, T. and Debra C. Peters} } @conference {51086, title = {Effects of plant removals on soil surface erosion in a Chihuahuan Desert shrubland}, booktitle = {85th Annual Meeting, Ecological Society of America}, year = {2000}, month = {August 6-10, 200}, pages = {290}, address = {Snowbird, UT}, abstract = {Humans are dramatically altering the patterns of biological diversity in semiarid ecosystems worldwide, in particular by altering the relative abundance of different growth forms (shrubs vs. perennial grasses) and by reducing the numbers of species within growth forms. We are exploring the impact of reduced plant diversity in experimental plots of creosotebush (Larrea tridentata) shrubland at the Jornada Basin LTER site near Las Cruces, NM, USA. In 1995, eight treatments of varying severity of plant community alteration were imposed on 25m x 25m plots (six replicates of each treatment); treatments ranged from no removals to extreme simplification of the perennial community (one shrub species, one grass species, one succulent, etc.). These treatments have been maintained since 1995. We have monitored soil erosion and sediment movement within these plots since spring 1996 by collecting sediment in pans at the downslope edge of each plot. Fine materials (particle diameter <2mm) dominate total soil movement (by weight), although larger particles are transported in this system, especially during the summer-fall season of intense episodic rainfall. Fine particle movement is higher in shrub removal and grass removal treatments than in controls during some seasons, especially in the summer. No statistically significant differences were detected during other seasons. Location on the slope with respect to local channels or arroyos contributes significantly to variation in the amount of material moving within a plot, as does the nature of vegetative cover and soil surface characteristics in the immediate vicinity of a collecting pan. Our results suggest the relationship between plant community structure and soil erosion rates is best examined at the scale of local patches.}, keywords = {Chihuahuan Desert, plant removal, shrubland, soil erosion}, author = {L. Huenneke and M. Buonopane and Bothern, L. and Jeffrey E. Herrick} } @article {51087, title = {Multivariate characterization of perennial vegetation in the northern Chihuahuan Desert}, journal = {Journal of Arid Environments}, volume = {44}, number = {3}, year = {2000}, month = {March 1, 2000}, pages = {305-325}, abstract = {

We surveyed vegetation at 100 sites in southern New Mexico to establish a benchmark for monitoring vegetation change. Sites were selected in a stratified random design based on a classified AVHRR image. Two shrubs (Larrea tridentata and Prosopis glandulosa) are the most important contributors to perennial cover in the area. Principal components analysis (PCA) and detrended correspondence analysis (DCA) both clearly delineate these shrublands from the smaller number of compositionally varied grassland sites. A latitudinal trend in DCA axis 1 scores suggests that encroachment of shrubs into grasslands is most pronounced in the southern portion of the study area.

}, keywords = {Chihuahuan Desert, Larrea tridentata, perennial vegetation, prosopis glandulosa}, doi = {10.1006/jare.1999.0597}, url = {/files/bibliography/00-005.pdf}, author = {A. R. Johnson and S.J. Turner and Walter G. Whitford and A.G. de Soyza and Justin Van Zee} } @article {51088, title = {Impact of grazing and desertification in the Chihuahuan Desert: Plant communities, granivores and granivory}, journal = {American Midland Naturalist}, volume = {144}, number = {1}, year = {2000}, month = {July 1, 2000}, pages = {78-91}, abstract = {

Livestock effects on plant communities through overgrazing (desertification) should affect the structure and functioning of semiarid rangeland communities. We measured plant, granivorous ant and rodent communities and rates of seed removal by rodents and ants in grazed (by livestock) and ungrazed desert grasslands, as well as mesquite and creosotebush shrublands to test hypotheses on the effects of grazing and desertification on ecosystem structure and functioning. In desert grasslands, grazing reduced the cover of perennial grasses, particularly the dominant Bouteloua eriopoda, but the cover of forbs and shrubs did not differ between treatments. One species of perennial grass, Dasyochloa pulchellum, increased in grazed grasslands compared with grassland exclosures. Detrended correspondence analysis showed that grazing caused desert grasslands to shift in community structure towards the shrublands. There were more seed harvesting ant and rodent species in the creosotebush shrublands than in the grasslands and mesquite shrublands. Grazing had no effect on the diversity of ants or rodents within grasslands, and detrended correspondence analysis revealed no clear trends in granivorous ant community structure in the grazed and ungrazed grasslands or the mesquite and creosotebush shrublands. Ants removed more seeds than did rodents in the grassland sites, but rodents removed more seeds than did ants in the creosotebush sites; seed removal rates by rodents and ants were the same in the mesquite sites. Our data support the hypothesis that livestock grazing leads to a shift from grassland to shrubland in the Chihuahuan Desert with associated changes in the structure and functioning of faunal communities. Because grasslands support few species and low densities of rodents, seed harvesting ants are the most important granivores in these desert grasslands. On a larger scale, we therefore hypothesize that the observed dominance of rodents as seed harvesters in the Chihuahuan Desert is a function of the desertification of desert grasslands to shrublands by livestock and that associated feedback effects may complicate the regeneration of degraded communities.

}, keywords = {Chihuahuan Desert, desertification, granivores, granivory, grazing, livestock, overgrazing}, doi = {10.1674/0003-0031(2000)144[0078:IOGADI]2.0.CO;2}, url = {/files/bibliography/00-010.pdf}, author = {G. I. H. Kerley and Walter G. Whitford} } @article {51094, title = {Microbial diversity and activity of disturbed soil in the northern Chihuahuan Desert}, journal = {Biology and Fertility of Soils}, volume = {32}, number = {3}, year = {2000}, month = {July 1, 2000}, pages = {243-249}, abstract = {

The effects of intense grazing, seasonal drought, and fire on soil microbial diversity (substrate utilization) and activity in a northern Chihuahuan Desert grassland were measured in summer 1997, winter 2998, and spring 1998. Intense livestock grazing was initiated in winter 1995, burning occurred in August 1994, and drought stresses were imposed from October 1994 to June 1997. Microbial diversity was inferred from the carbon substrate utilization patterns in both gram (+) and gram (-) Biolog plates. Microbial activity was estimated by the activity of selected enzymes. Neither microbial diversity nor activity was affected by grazing. The interaction of intense grazing and stress subtreatments only occurred in spring for one set of diversity measurements. The maximum microbial diversity and activity occurred in the winter-drought-stress subplots in summer and spring. Burning reduced microbial diversity and most enzyme activities as compared to the control in summer and spring. Microbial diversity was also lower in summer-drought-stress subplots than in the control in summer and spring. Microbial diversity was highest in summer, intermediate in winter, and lowest in spring. Microbial activity was generally higher in summer and lower in winter. It was concluded that substrate availability was the most important factor affecting the diversity and activity of soil microorganisms within a season. Soil moisture was not the factor causing differences in microbial diversity and activity among the stress treatments, but it was a predictor for some microbial responses under a particular stress.

}, keywords = {Chihuahuan Desert, grazing, microbial diversity, soil}, doi = {10.1007/s003740000242 }, url = {/files/bibliography/00-011.pdf}, author = {Liu, X. and W. C. Lindemann and Walter G. Whitford and R.L. Steiner} } @article {51098, title = {Ant (Hymenoptera: Formicidae) responses to environmental stressors in the northern Chihuahuan Desert}, journal = {Community and Ecosystem Ecology}, volume = {29}, number = {2}, year = {2000}, month = {April 1, 2000}, pages = {200-206}, abstract = {

We studied responses of ant communities to shrub removal and intense, pulse seasonal grazing by domestic livestock for four consecutive years. Weighted relative abundance and percent of traps in which an ant species occurred were analyzed using randomized, complete block design split in time analysis of variance to test for significant differences between means of ant groups. The ant community in the Chihuahuan Desert grassland is dominated by small, liquid-feeding ants, Conomyrma insana (Buckley), and large seed harvesting ants, Pogonomyrmex desertorum (Wheeler). The weighted relative abundance of C. insana was significantly reduced on the plots without shrubs. The relative abundance of P. desertorum was significantly lower on grazed plots without shrubs than on the ungrazed plots without shrubs. There were no detectable effects of shrub removal or intense, pulse grazing on the less abundant ant species. These results suggest the recent encroachment of shrubs into Chihuahuan Desert grasslands has increased the relative abundance of the dominant ant species in these communities. Intensive grazing by livestock has had an adverse effect on the most abundant seed-harvester, P. desertorum.

}, keywords = {ant, Chihuahuan Desert, environmental stressors, Hymenoptera: Formicidae, pulse grazing, shrub removal}, doi = {10.1093/ee/29.2.200}, url = {files/bibliography/00-007_0.pdf}, author = {M. S. Nash and Walter G. Whitford and Justin Van Zee and Kris Havstad} } @proceedings {51117, title = {Estimation of surface emissivity for arid lands}, volume = {IAHS Publication No. 267}, year = {2000}, month = {2001}, pages = {168-174}, publisher = {Remote Sensing and Hydrology}, address = {Santa Fe, NM}, abstract = {

Knowledge of surface emissivity is important for determining the radiation balance at the land surface. For heavily vegetated surfaces there is little problem since the emissivity is relatively uniform and close to one. For arid lands with sparse vegetation the problem is more difficult because the emissivity of the exposed soils and rocks is highly variable. With multispectral thermal infrared (TIR) observations it is possible to estimate the spectral emissivity variation for these surfaces. The data presented is from the TIMS (Thermal Infrared Multispectral Scanner) instrument which has six channels in the 8 to 12 {\textmu}m region. TIMS is a prototype of the TIR portion of the ASTER (Advanced Spaceborne Thermal Emission and Reflection radiometer) instrument on NASA{\textquoteright}s EOS-TERRA satellite. The approach is to use the Temperature Emissivity Separation (TES) algorithm developed for use with ASTER data to extract the temperature and six emissivities from the six channels of TIMS data. The algorithm makes use of the empirical relation between the range of observed emissivities and their minimum value. This approach was applied to the TIMS data acquired over the USDN ARS Jornada Experimental Range in New Mexico. The Jornada site is typical of a desert grassland where the main vegetation components are grass (black grama) and shrubs (primarily mesquite) in the degraded grassland. The data are from an altitude of 800 m yielding a pixel resolution of approximately 2 m. The result-ing spectral emissivities are in qualitative agreement with laboratory measurements of the emissivity (E) for the quartz rich soils of the site with{\textsterling}\< 0.8 for the 8-9.5 {\textmu}m channels. For the longest wavelength channel little spatial variation of{\textsterling} was observed with values of0.96 {\textpm} 0.005 over large areas.

}, keywords = {arid lands, ASTER, Chihuahuan Desert, emissivity, Jornada, multispectral, surface temperature, Thermal infrared, TIMS}, url = {/files/bibliography/01-081.pdf}, author = {T. J. Schmugge and A.N. French and Jerry Ritchie and A. Rango} } @article {51128, title = {Arroyo water storage and soil nutrients and their effects on gas-exchange of shrub species in the northern Chihuahuan Desert}, journal = {Journal of Arid Environments}, volume = {43}, number = {1}, year = {1999}, month = {1999}, pages = {21-33}, abstract = {

A variable fraction of the rain falling on desert landscapes runs off and accumulates in ephemeral channels (arroyos), where some of the water is transported downslope. Relatively large amounts of water are stored in arroyo sediments. This water may support high rates of gas-exchange in some riparian species. We examined differences in the timing of flow events, soil water storage, and soil nutrients on gas-exchange rates of shrubs growing on arroyo margins and in adjacent piedmont areas in the Chihuahuan Desert of southern New Mexico, USA. The semi-riparian shrub, Fallugia paradoxa (Apache plume), had very different photosynthetic rates between two arroyos, but transpiration rates did not differ. This may result from nutrient limitation differences between arroyos. At one site, the semi-riparian shrub, Prosopis glandulosa (mesquite), on arroyo margins had access to more water and showed higher rates of gas-exchange compared with non-arroyo mesquite located on nearby piedmont areas. The obligate riparian shrub, Chilopsis linearis (desert willow), had intermediate gas-exchange rates when compared with Apache plume and mesquite, and neither soil water nor nutrient concentrations appeared to affect photosynthesis during the growing season. Variation between and within arroyos was high; however, our data suggest that stored water enabled mesquite of arroyo margins to maintain relatively high rates of gas-exchange. When water was relatively abundant, nutrient availability appeared to limit photosynthetic rates of Apache plume. (C) 1999 Academic Press.

}, keywords = {Chihuahuan Desert, Chilopsis linearis, fallugia paradoxa, photosynthesis, prosopis glandulosa, soil nutrients, soil water storage, transpiration}, doi = {10.1006/jare.1999.0530}, url = {/files/bibliography/643.pdf}, author = {Atchley, M.C. and A.G. de Soyza and Walter G. Whitford} } @article {51144, title = {Burrowing activities of kangaroo rats and patterns in plant species dominance at a shortgrass steppe-desert grassland ecotone}, journal = {Journal of Vegetation Science}, volume = {10}, year = {1999}, month = {1999}, pages = {123-130}, abstract = {

Our objective was to evaluate the effects of burrowing activities by banner-tail kangaroo rats (Dipodomys spectabilis Merriam) on plant community structure and species dominance for two patch types at the ecotone between shortgrass steppe and desert grassland in New Mexico, USA. 10 mounds produced by kangaroo rats were selected in patches dominated by Bouteloua gracilis (the dominant in shortgrass steppe communities) and 10 mounds were selected in patches dominated by B. eriopoda (the dominant in Chihuahuan desert grasslands). Plant cover and density by species were sampled from three locations associated with each mound: the mound proper, the edge of the mound in the transition area, and the off-mound vegetation. Similar cover of B. eriopoda for the edges of mounds in both patch types indicates the ability of this species to respond to animal disturbances regardless of the amount of cover in the surrounding undisturbed vegetation. By contrast, cover of B. gracilis was low for all mounds and mound edges in patches dominated by this species. Much higher cover of B. eriopoda on mound edges compared to the undisturbed vegetation in B. gracilis-dominated patches indicates that kangaroo rats have important positive effects on this species. Lower cover of perennial grasses and higher cover of forbs, shrubs, and succulents on the edges of mounds in B. eriopoda-dominated patches compared to patches dominated by B. gracilis indicate the importance of surrounding vegetation to plant responses on disturbed areas.

}, keywords = {Bouteloua, Chihuahuan Desert, Dipodomys spectabilis, disturbance, dominant species, kangaroo rat}, doi = {10.2307/3237167}, url = {/files/bibliography/654.pdf}, author = {Fields, M.J. and D.P. Coffin and J. R. Gosz} } @article {51249, title = {Early warning indicators of desertification: Examples of tests in the Chihuahuan Desert}, journal = {Journal of Arid Environments}, volume = {39}, number = {2}, year = {1998}, month = {June 1, 1998}, pages = {101-112}, abstract = {

Perennial grasslands that dominated the south-west United States during the past 10,000 years have been desertified to varying extents. Desertification is a temporal phenomenon, defined in this paper as a change in the scale of the spatial distribution of resources. We report here on several indicators of desertification, using bare patch indices as surrogates for direct measures. A bare patch index based on canopy cover, which is relevant for precipitation and wind-driven erosion, is not equivalent to another bare patch index based on soil surface measurements, which is relevant for overland water flow-driven erosion. Per cent grass cover, per cent long-lived grass cover, per cent cover of vegetative reproducers, and a relative preference index all yielded sensitive indicators of desertification. The usefulness of some indicators, such as organic litter, depends upon recent environmental history. Other indicators, such as per cent cover due to grazing-resistant species, appear not to be sensitive to desertification and need further development. Range site type may also be important in determining indicator responses, where some indicators were sensitive to a range site while others were not. Overall, we have identified several sensitive indicators of desertification based on vegetational characteristics in varied range sites in the northern Chihuahuan Desert.

}, keywords = {bare patch index, Chihuahuan Desert, ecosystem health, indicators, litter}, doi = {10.1006/jare.1998.0391}, url = {/files/bibliography/607.pdf}, author = {A.G. de Soyza and Walter G. Whitford and Jeffrey E. Herrick and Justin Van Zee and Kris Havstad} } @proceedings {51211, title = {Rangeland research in the Chihuahuan Desert}, year = {1998}, month = {1998}, keywords = {cattle growers{\textquoteright} short course, Chihuahuan Desert, rangeland, research}, author = {Richard E. Estell and D.M. Anderson and J.R. Barrow and A.G. de Soyza and E.L. Fredrickson and Gibbens, Robert P. and Kris Havstad and Jeffrey E. Herrick and M.R. Tellez and Walter G. Whitford} } @article {51385, title = {Tarbush leaf surface terpene profile in relation to mammalian herbivory}, journal = {Journal of Chemical Ecology}, volume = {24}, year = {1998}, month = {January 1998}, pages = {1-12}, abstract = {

Tarbush (Flourensiacernua DC.) is a generally unpalatable shrub native to the Chihuahuan Desert and with a resinous leaf surface containing several terpenes. Tarbush epicuticular wax concentration has previously been linked to degree of use by livestock in our laboratory. In 1989 and 1990, cattle, sheep, and goats were densely stocked in tarbush-containing paddocks for 6 to 9 days. Degree of use of 20 permanently marked plants in each paddock (8 paddocks, 2 sites, only 10 plants were monitored in 4 of the paddocks the first year) was recorded daily both years. Thus, no destructive sampling of plants was possible. A high percentage of tarbush in diets and differential use of individual tarbush plants were observed in this companion study. In 1991, leaves were collected from these plants (n = 160) during the same stage of maturity. Leaf surface compounds were extracted with ethanol, and mono- and sesquiterpenes were analyzed using gas chromatography/ion trap mass spectrometry. Our objective was to examine whether degree of tarbush use during the high-density study was related to chemistry of the same plants the following year. Plants were separated into three categories after preliminary data evaluation (Category 1: \> 50\% use at period midpoint; Category 2: \< 50\% use at midpoint but \> 50\% use at period end; Category 3: \< 50\% use at period end). Multivariate analysis is being used to examine relationships of individual plant use with dry matter, ash, epicuticular wax, and several individual and subgroups of mono- and sesquiterpenes (oxygenated and hydrocarbon monoterpenes and sesquiterpenes). Preliminary evaluation suggests chemical subgroup variables in 1991 were related to degree of herbivory in 1989 and 1990, although statistical analyses are not complete. Monoterpene hydrocarbons, oxygenated monoterpenes, and oxygenated sesquiterpenes were all sign different for the three use categories. We will determine which individual compounds contribute to these differences. Estimated concentrations of unidentified compounds will also be evaluated. One assumption is that heavy browsing during 1989 and 1990 did not cause plant secondary chemistry changes which persisted in 1991. Of the 120 plants with use data for both years, 66 plants in a given use category for 1989 were in the same category in 1990 and 38 plants were in a higher category. Only 15 plants fell to a lower use category and only 1 plant dropped from Category 1 to 3. Based on these observations, degree of use was reasonably consistent for individual plants across years, suggesting that, at least between 1989 and 1990, if induction occurred, it was short term. Leaf surface chemistry appears to be related to degree of use of individual tarbush plants by livestock.

}, keywords = {Chihuahuan Desert, leaf surface, mammalian herbivory, tarbush, terpene profile}, doi = {10.1023/A:1022399426352}, url = {/files/bibliography/512.pdf}, author = {Richard E. Estell and E.L. Fredrickson and D.M. Anderson and Kris Havstad and M.D. Remmenga} } @article {51216, title = {Perspectives on desertification: Southwestern United States}, journal = {Journal of Arid Environments}, volume = {39}, year = {1998}, month = {1998}, pages = {191-207}, abstract = {

Several climatic changes occurred in the northern Chihuahuan Desert and other parts of the southwest United States during the last 12,000 years leading to a markedly warmer and drier climate.\  Vegetation changed in response to this climatic shift. Generally, this transition was from coniferous woodland to grasslands and eventually to the present day desert scrub.\  Pre-Columbian inhabitants of this region adapted by changing from hunter-gatherer to primarily agrarian economics.\  European immigrations into the southwest U.S. beginning in the mid 1500s greatly affected this region.\  The greatest impact occurred after the U.S. Civil war in the 1860s.\  Before that time land use tended to be localized near small agricultural areas, mines, and military installations.\  The post-war range livestock industry expanded dramatically, especially during the 1880s {\textendash} a period of general abuse of arid lands in the region.\  Recognition of this abuse and the deteriorating productivity of the land led to greater government involvement, including establishment of experimental stations and eventually management of the public domain by governmental agencies.\  Fire suppression, mismanaged grazing, changing climatic conditions, loss of soil and increasing atmospheric CO2 concentrations, mainly due to the burning of fossil fuels, are among the probable causes of continued desertification trends\ \  Urban and rural populations, presently technologically isolated from their environment, need to better understand the dynamic nature of their environment.\  A greater degree of co-operation among diverse entities will be crucial.

}, keywords = {Chihuahuan Desert, desertification, Sonoran Desert, south-west United States}, doi = {10.1006/jare.1998.0390}, url = {/files/bibliography/613.pdf}, author = {E.L. Fredrickson and Kris Havstad and Richard E. Estell and P.W. Hyder} } @article {51241, title = {Changes in mass and chemistry of plant roots during long-term decomposition on a Chihuahuan Desert watershed}, journal = {Biology and Fertility of Soils}, volume = {26}, year = {1998}, month = {1998}, pages = {16-22}, abstract = {

We studied the spatial and temporal patterns of decomposition of roots of a desert sub-shrub, a herbaceous annual, and four species of perennial grasses at several locations on nitrogen fertilized and unfertilized transects on a Chihuahuan Desert watershed for 3.5 years. There were few significant differences between the decomposition rates of roots on the NH4NO3 fertilized and unfertilized transects. Decomposition of all roots followed a two-phase pattern: early rapid mass loss followed by a long period of low mass loss. Rates of decomposition were negatively correlated with the initial lignin content of the roots (r=0.90). Mass loss rates of the roots of the herbaceous annual, Baileya multiradiata, were significantly higher than those of the grasses and the shrub, probably as a result of subterranean termites feeding on B. multiradiata root material. The only location where mass loss rates were significantly different was the dry lake bed, where mass loss rates were lower than those recorded on the upper watershed. The spatial differences in mass loss rates in the dry lake were attributable to the high clay content of the soils, which reduced water availability, and to the absence of termites. Non-polar substances in decomposing roots decreased rapidly during the first year, then decreased at a low but fairly constant rate. Water-soluble compounds decreased rapidly (50{\textendash}60\% of initial concentration) during the first 3{\textendash}6 months. Lignin concentrations of roots of perennial grasses were higher than those of herbaceous annual plants and woody shrubs. Lignin concentrations increased in all species during decomposition. The chemical changes in decomposing roots followed the patterns described for decomposing litter in mesic environments.

}, keywords = {Chihuahuan Desert, decomposition, Lignin, Mass loss, nitrogen immobilization}, doi = {10.1007/s003740050336}, url = {/files/bibliography/629.pdf}, author = {Hyeong-Tae Mun and Walter G. Whitford} } @proceedings {51272, title = {Rangeland research in the Chihuahuan Desert}, year = {1997}, month = {1997}, keywords = {cattle growers{\textquoteright} short course, Chihuahuan Desert, rangeland, research}, author = {Richard E. Estell and D.M. Anderson and J.R. Barrow and A.G. de Soyza and E.L. Fredrickson and Gibbens, Robert P. and Kris Havstad and Jeffrey E. Herrick and M.R. Tellez and Walter G. Whitford} } @article {51290, title = {Mechanisms for the keystone status of kangaroo rats: graminivory rather than granivory?}, journal = {Oecologia}, volume = {111}, year = {1997}, month = {1997}, pages = {422-428}, abstract = {

Graminivory by kangaroo rats (Dipodomys spp.) was investigated as a potential mechanism for the keystone role of these rodents in the dynamics of desert grasslands. Experiments confirmed that Ord{\textquoteright}s kangaroo rats (Dipodomys ordii) cut and consumed a large proportion of the tillers of three Chihuahuan Desert tussock-forming grass species. Field observations indicated that the characteristically cut grass tillers were absent from all-rodent and medium-sized kangaroo rat exclosures, but were frequent in large-sized kangaroo rat and rabbit exclosures, indicating that the medium-sized kangaroo rats (D. ordii, D. merriami) were responsible for grass cutting. Tiller waste as a percentage of peak standing crop ranged from 7\% in grassland habitats to 0.7\% in Flourensia cernua shrubland. Of the 13 species of perennial, tussock-forming grasses measured, only one, Muhlenbergia porteri, had no tillers cut by kangaroo rats. This study demonstrates that the keystone role of kangaroo rats in Chihuahuan Desert grassland ecosystems is probably the result of their graminivory.

}, keywords = {Chihuahuan Desert, Dipodomys, graminivory, Grass populations, keystone species}, doi = {10.1007/s004420050254}, url = {/files/bibliography/591.pdf}, author = {G. I. H. Kerley and Walter G. Whitford and F. R. Kay} } @article {51362, title = {Stemflow, throughfall and channelization of stemflow by roots in three Chihuahuan Desert shrubs}, journal = {Journal of Arid Environments}, volume = {32}, year = {1996}, month = {1996}, pages = {271-287}, abstract = {

Three studies were conducted to examine precipitation{\textendash}vegetation relationships in the multi{\textendash}stemmed shrubs Larrea tridentata, Prosopis glandulosa and Flourensia cernua in a desert ecosystem. We measured stemflow and throughfall as affected by bulk precipitation, canopy architecture and stem-angles. Using fluorescent dye, we traced root channelization of stemflow water. Stepwise regression analysis showed that the best one-variable model for stemflow in L. tridentata was canopy volume, which accounted for 87\% of variation. The best one-variable model for stemflow in P. glandulosa and F. cernua was canopy area, which accounted for 82\% of variation in both species. Stemflow data from winter and summer months were statistically compared to determine the influence of leaves on stemflow generation in P. glandulosa and F. cernua. Stemflow amounts collected during winter months do not differ significantly from those of summer months demonstrating that in these winter deciduous species the absence of leaves during winter months does not affect generation of stemflow. Analysis of variance showed that the percentage of throughfall was different among species suggesting that variations in canopy characteristics could explain, in part, these interspecific throughfall differences. Both stem-angle and stem-length had a significant effect on stemflow generation in F. cernua and L. tridentata, whereas there was only a significant relationship between stem-angle and stemflow in P. glandulosa. Analysis of rhodamine-B dye distribution under shrubs indicated that root channels are preferential pathways for movement of stemflow water into soil, and that this water is potentially the source of soil moisture which allows shrubs to remain physiologically active under drought conditions.

}, keywords = {Chihuahuan Desert, Flourensia cernua, Larrea tridentata, prosopis glandulosa, root channelization, stemflow, throughfall}, doi = {10.1006/jare.1996.0023}, url = {/files/bibliography/500.pdf}, author = {E. Martinez-Meza and Walter G. Whitford} } @conference {51422, title = {Responses of plant assemblages to disturbance gradients in the northern Chihuahuan Desert}, booktitle = {Winter Meeting of the British Ecological Society}, year = {1995}, month = {December 19-21, }, pages = {71}, address = {University of Sheffield, GB}, abstract = {At three locations in the Chihuahuan Desert, domestic livestock-induced disturbance gradients extend outward from watering points. Soil is more compacted but less stable near the watering points. Plant species richness changes little along the gradient, but species diversity and plant biomass does increase dramaatically with distance from the watering point.}, keywords = {Chihuahuan Desert, disturbance gradients, plant assemblages, species diversity}, author = {A.G. de Soyza and Justin Van Zee and Walter G. Whitford and Jeffrey E. Herrick} } @proceedings {51394, title = {Rangeland research in the Chihuahuan Desert}, year = {1995}, month = {1995}, abstract = {

Three major classes of symbiotic fungi were identified in the roots of native grasses and shrubs on arid rangelands of the southwestern U.S. The first class is vesicular-arbuscular mycorrhizae, common to most higher plants. These fungi enhance nutrient and water uptake in plants. The second major class of symbiotic fungi are common soil or saprobic fungi. Because of their association with the host plant their capacity is enhanced to access nutrients from immobile inorganic and complex organic resources and supply them to the plant. One demonstrated benefit of a saprophytic seed-borne fungus, Alternaria alternata, was that it decomposed the seed capsule at germination and transferred nutrients to the germinating seedling, improving chances for survival and establishment. {\textquoteright}These fungi likely play a role in the management of carbon resources in the ecosystem. Third major class of fungi regularly associated with grass and shrub roots were Chytridiomycetes, a primitive aquatic fungus. These fungi appear to regulate the colonization by the other two fungal classes. These fungi, acting in concert with each other, enhance nutrient and water uptake of native plants. They directly affect survival ability and competitiveness of all plant species in arid rangelands. We are researching these fungi because we think that new technologies for rangeland revegetation of degraded areas will require the presence of these fungal classes for successful reestablishment and survival of native plant species.

}, keywords = {cattle growers{\textquoteright} short course, Chihuahuan Desert, rangeland, research}, url = {/files/bibliography/446.pdf}, author = {Kris Havstad and D.M. Anderson and J.R. Barrow and Richard E. Estell and E.L. Fredrickson and Gibbens, Robert P. and Jeffrey E. Herrick and Walter G. Whitford} } @conference {51399, title = {Contribution of ant activity to spatial variability in hydrologic properties in the Chihuahuan Desert}, booktitle = {American Society of Agronomy Meeting}, year = {1995}, month = {October 29-Novem}, pages = {Abstract 309}, abstract = {The activity of soil fauna is frequently cited as a factor contributing to the spatial variability of arid rangeland soils in the southwestern United States. However, few studies have correlated differences in soil physical properties with the activity of specific soil organisms. In order to quantify the contribution of ant activity to spatial variability in surface macroporosity, infiltration rates under ponding and under tension at the center and margins of harvester ant (Pogonomyrmexrugosus) nests were compared with rates in adjacent, nonvegetated control sites. Both saturated hydraulic conductivity and the difference between saturated and unsaturated conductivity were highest at the nest centers. These results illustrate the role of ants in the creation of macropores capable of conducting water under conditions of overland flow. The results will be discussed with respect to patterns and densities of ant nests in the Chihuahaun Desert.}, keywords = {ant activity, Chihuahuan Desert, hydrologic properties, macropores, spatial variability}, author = {Jeffrey E. Herrick and Walter G. Whitford} } @conference {51453, title = {Approaches to assessing the quality of rangeland soils}, booktitle = {American Society of Agronomy Meeting}, year = {1994}, month = {November 13-18, }, pages = {Abstract 285}, abstract = {Soil quality can be defined as the soil{\textquoteright}s capacity to perform selected functions, to resist degradation, and to recover following disturbance. It depends on interactions between the soil, soil fauna, and vegetation, and, therefore, may serve as a useful integrated indicator of overall ecosystem condition. Definitions of ecosystem condition, however, depend on management objectives. We will present an approach for calibrating indicators of semiarid rangeland soil quality for a variety of management objectives. This integrated approach will be illustrated with preliminary data from a study of semiarid rangeland in the Chihuahuan Desert. These data, together with other recent studies, suggest that spatial patterns may be as useful as average values of soil properties in assessing soil quality for noncultivated systems.}, keywords = {assessing quality, Chihuahuan Desert, rangeland soils}, author = {Jeffrey E. Herrick and Walter G. Whitford} } @proceedings {51486, title = {Technologies for sustainable development of Chihuahuan Desert rangelands}, volume = {12}, year = {1993}, month = {1993}, abstract = {Options for management of Chihuahua Desert rangelands have been recently viewed as limited. Many technologies that had typically been seen as viable components of management have become expensive, inefficient, or inappropriate. Yet, the need for management of these desert rangelands is increasingly urgent. It is evident that simply withdrawing lands from use will not generally lead to improvements in resource values or restoration of prior condition. Human interventions are required, but the nature of those interventions must be based on knowledge of the ecological integrity of these lands. We view the northern Chihuahuan Desert as a complex and chaotic system. Management tools must be viewed as triggers for change within this complexity rather than obtrusive instruments for large scale alterations to the landscape. One trigger mechanism is domestic livestock. Planned manipulations of livestock grazing behaviors may achieve desirable changes in vegetation structure. Another trigger is selective reintroduction of germplasm. Seed dispersal technologies which rely on natural elements, such as animal, wind, and water, may slowly affect bioremediation with minimal impacts to other resources and with minimal expense. Development of these look requires detailed process level knowledge of the desert ecosystem. We are beginning to achieve this understanding through interdisciplinary and interinstitution research. However, we need to further expand these collaborations, especially internationally, to best develop livestock and revegetation tools that will be applicable for sustainable development throughout the Chihuahuan Desert.}, keywords = {Chihuahuan Desert, rangelands, sustainable development}, author = {Kris Havstad} } @mastersthesis {51506, title = {Diurnal diet composition and behavior of cattle and sheep on Chihuahuan Desert range}, volume = {PhD}, year = {1993}, note = {Available in JER Library}, month = {1993}, pages = {162 }, school = {New Mexico State University}, type = {Dissertation }, address = {Las Cruces}, keywords = {behavior, cattle, Chihuahuan Desert, diet composition, dissertation, diurnal, research notes, sheep}, author = {J. N. Smith} } @conference {51527, title = {Perceptions from review of 80 years of range research in the Chihuahuan Desert}, booktitle = {Annual Meeting, Society for Range Management}, year = {1992}, month = {1992}, pages = {No. 086}, abstract = {Rangeland research has been conducted in the northern Chihuahuan Desert of southern New Mexico for the past 80 years. Early scientists with the well recognized names of Jardine, Forsling, and Chapline, were followed by Campbell, Canfield, and Parker and, more recently, by Paulsen and Herbel. Their research efforts were impressive and productivity was substantial. Four observations from a review of their published record are: (1) Basic tenets of management were established in the early 1920s while later research simply refined and/or slightly expanded these tenets. (2) Range improvement has been a constant thrust, but many tools resulting from this research are not currently applicable. (3) Current management concerns remain poorly assessed, especially as related to applicable data on grazing capacity and vegetation dynamics. (4) And, recent research efforts are more diverse, basic, descriptive and less directly applicable to management needs. It could be concluded that range science has failed to illuminate principles applicable to today{\textquoteright}s management issues in the Southwest. This general viewpoint and the viewpoint that range science and range management are separate but complementary endeavors have been recently expressed (Provenza, F.D., 1991, JRM 44:281-183). However, review of literature (especially from biological sciences) presents numerous basic principles with application to rangelands. The present deficit is lack of application of these principles by range researchers to the development of tools and new uses of current tools suitable for management goals given the reality of present day constraints. A recent survey of future range research topics indicates ecology and improvements as top priorities with a scattering of other interests (Hardesty, L.H., 1991, JRM 44:289-294). To effectively use the next 80 years of research we must continually identify current management needs, utilize applicable principles identified from all scientific fields, and emphasize development of usable tools.}, keywords = {application of principles, Chihuahuan Desert, management issues, perceptions, range research}, author = {Kris Havstad} } @conference {51546, title = {Fungal interactions of key Chihuahuan Desert grasses}, booktitle = {Annual Meeting, Society for Range Management}, year = {1992}, month = {1992}, pages = {Abstract No. P039}, abstract = {Fungal symbionts are recognized as important in the ecology of desert plant communities.Mycorrhizal associations can influence plant establishment, growth, and reproduction. In the Chihuahuan Desert two of the dominant shrubs (Larrea tridentata and Prosopis glandulosa) are recognized as endomycorrhizal, an attribute which may contribute to the competitiveness of these species in this environment. We hypothesize that principle native perennial grasses may not effectively exploit mycorrhizal associations. Our initial study objective was to examine the nature and extent of mycorrhizal infections of six key native perennial grass species found in association with these shrubs. Bouteloua eriopoda, Aristida longiseta. Sporobolus flexuosus,Hilana mutica, Muhlenbergia porteri, and Scleropogon brevifolius specimens were collected biweekly from June through September, a schedule which bracketed the summer growing season. Staining techniques identified histochemical activities as related to mycorrhizal structures, including vesicles and arbuscules. Separation techniques isolated fungal spores for inoculation of a nonendemic host and subsequent species identification. Data will be presented on the temporal nature of mycorrhizal infection of these perennial grasses. It is assumed that differential fungal symbiont activities may partly explain vegetation dynamics and soil microflora requirements for subsequent restoration of perennial grasses.}, keywords = {Chihuahuan Desert, desert plant communities, ecology, fungal interactions, grasses, mycorrhizal associations, symbionts}, author = {Saar, L.J. and J.R. Barrow and Kris Havstad} } @article {51565, title = {Some effects of precipitation patterns on mesa dropseed phenology}, journal = {Journal of Range Management}, volume = {44}, number = {1}, year = {1991}, note = {Permission to post articles granted by the Society for Range Management; www.rangelands.org.}, month = {January 1, 1991}, pages = {86-90}, abstract = {

Phenology of mesa dropseed [Sporobolus flexuosus (Thurb.) Rydb.] was studied from 1979 to 1987 on the Jornada Experimental Range in southern New Mexico. Growing season (March through November) precipitation ranged from 99 to 308 mm during the 8-year period. Foliage height and number of leaves were recorded weekly for individually marked culms on 20 plants. New culms usually appeared during the first week in March and green leaf tissue often persisted until the end of November. Correlation analyses of accumulated weekly height increments and accumulated weekly precipitation showed that growth was highly dependent upon rainfall (r = 0.81 to 0.97). Leaf formation was also correlated with rainfall (r = 0. 79 to 0.98). Even in relatively wet years there were 1 or 2 periods of no growth. In drier years, no growth periods totaled as much as 87 days. Periods of rapid growth occurred only after rainfall events \> 13 mm. The first exsertion of seed heads occurred as early as the last week of July and as late as the second week of October. The temporal plasticity of mesa dropseed phenology indicates that it is well adapted to the arid environment.

}, keywords = {arid zones, Chihuahuan Desert, grass growth, leaf development, rangeland, Sporobolus flexuosus}, doi = {10.2307/4002646 }, url = {/files/bibliography/367.pdf}, author = {Gibbens, Robert P.} } @conference {51571, title = {Environmental effects on behavior and production of range cows on the Chihuahuan Desert}, booktitle = {Annual Meeting of the Society for Range Management}, year = {1991}, month = {1991}, pages = {No. 88}, abstract = {

Behavior of free-ranging cows was investigated as affected by season, diurnal periods, and weather parameters. Sixteen genetically diverse lactating cows were fitted with vibracorders to record active time continuously from 18 May 1989 to 3 January 1990. Total collection time was divided into three seasons: hot-dry (1 June to 12 July), warm-rain (1 August to 11 September), and cold-dry (1 November to 12 December). Days within seasons were divided into 24 1-hour periods. Differences in active time were found among seasons (P \< .05), periods (P \< .05), periods within seasons (P \< .05), and cows within periods within seasons (P \< .05). Activity was lowest during the hot-dry season during darkness. Substantial activity occurred during the hottest daytime periods. Warm-rain season activity during darkness increased (P \< .05) slightly with daytime period activity increasing substantially (P \< .05). Cold-dry season activity illustrated classical grazing periods with major post-dawn, pre-dusk, and nighttime period activity. Average total daily active times were 10.9 h, 12 h, and 9.5 h for hot-dry, warm-rain, and cold-dry seasons, respectively. Cows were very active during the hot periods of the day during the hot-dry season. Lowest total active time occurred during the cold-dry season when cows were not lactating and had low physiological requirements.

}, keywords = {behavior, Chihuahuan Desert, environmental effects, production, range cows}, author = {Horton, J. and Pieper, Rex D. and Kris Havstad and Wallace, J.D. and L. W. Murray} } @article {51600, title = {Runoff and erosion following mechanical and chemical control of creosotebush (Larrea tridentata) }, journal = {Weed Technology}, volume = {5}, year = {1991}, month = {1991}, pages = {48-53}, abstract = {

Runoff and sediment yield wer monitored from 1983 through 1986 on a range site dominated by creosotebush. The site was rootplowed and seeded, treated with tebuthiuron at 36 kg ai ha -1, or left untreated. Runoff from rootplowed and herbicide-treated plots was no different from untreated plots for 1 yr, but sedimetn yield from treated plots was lower than that from the untreated plots. Rootplowing and seeding increased sediment yield in the second year (1984), whereas treating with herbicide decreased sediment yield. Runoff and sediment yield during 1985 and 1986 were greatest from the untreated areas and least from the rootplowed and herbicide-treated areas. Total cover was nearly the same for each treatment. The untreated plots had 13\% shrub cover, the others had none. Between shrubs in untreated plots, bare ground occupied large interconnected areas that contributed to the higher runoff and erosion rates.

}, keywords = {Chihuahuan Desert, phytomass, rainfall, root plow, sediment yield, water stage}, url = {/files/bibliography/376.pdf}, author = {Wood, M. Karl and E.L. Garcia and J.M. Tromble} }