@article {JRN55373, title = {Mechanisms and drivers of alternative shrubland states}, journal = {Ecosphere}, volume = {13}, year = {2022}, month = {03 April 2022}, pages = {e3987}, abstract = {Grassland-to-shrubland state change has been widespread in arid lands globally. Long-term records at the Jornada Basin USDA-LTER site in the North American Chihuahuan Desert document the time series of transition from grassland dominance in the 1850s to shrubland dominance in the 1990s. This broadscale change ostensibly resulted from livestock overgrazing in conjunction with periodic drought and represents the classic {\textquotedblleft}grassland-to-shrubland{\textquotedblright} regime shift. However, finer-scale observations reveal a more nuanced view of this state change that includes transitions from dominance by one shrub functional type to another (e.g., based on leaf habit [evergreen vs. deciduous], N2 fixation potential, and drought tolerance). We analyzed the Jornada Basin historic vegetation data using a fine-scale grid and classified the dominant vegetation in the resulting 890 cells on each of four dates (1858, 1915, 1928, and 1998). This analysis allowed us to quantify on contrasting soil geomorphic units the rate and spatial distribution of: (1) state change from grasslands to shrublands across the Jornada Basin, (2) transitions between shrub functional groups, and (3) transitions from shrub-to-grass dominance. Results from our spatially explicit, decadal timescale perspective show that: (1) shrubland ecosystems developing on former grasslands were spatially and temporally more dynamic than has been generally presumed, (2) in some locations, shrublands initially developing on grasslands subsequently transitioned to ecosystems dominated by a different shrub functional type, with these changes in shrub composition likely involving changes in soil properties, and (3) some shrub-dominated locations have reverted to grass dominance. Accordingly, traditional, broad characterizations of {\textquotedblleft}grassland-to-shrubland{\textquotedblright} state change may be too simplistic. An accounting of these complexities and transitions from one shrub functional group to another is important for projecting state change consequences for ecosystem processes. Understanding the mechanisms, drivers, and influence of interactions between patterns and processes on transitions between shrub states defined by woody plant functional types will be germane to predicting future landscape change.}, keywords = {desertification, drylands, plant functional types, regime shifts, shrub growth form, shrubland transitions, Special Feature: Dynamic Deserts}, doi = {10.1002/ecs2.3987}, url = {files/bibliography/22-005.pdf}, author = {Steven R. Archer and Debra C. Peters and N. Dylan Burruss and Jin Yao} } @article {JRN55318, title = {Ecological theory and practice in arid and semiarid ecosystems: a tale of two LTER sites}, volume = {59}, year = {2021}, pages = {151-180}, publisher = {Archimedes (New Studies in the History and Philosophy of Science and Technology)}, abstract = {The chapter compares the conceptual history of two Long Term Ecological Research (LTER) programs at U.S. Department of Agriculture (USDA) research sites established following land overuse in the early 1900s. Early USDA studies were based on a Clementsian model, where vegetation following disturbance was expected to return to the climax determined by climate and soils. Management-based alternatives to the Clementsian model were developed after the dominant vegetation failed to recover and alternative states were observed. The Central Plains Experimental Range LTER (later Shortgrass Steppe LTER) program began in 1981 at a site in northern Colorado. Early studies focused on the inability of the dominant species, blue grama (Bouteloua gracilis), to recover on long-abandoned agricultural fields. These observations were in contrast to the resilience of blue grama-dominated ecosystems in response to livestock grazing and drought. The Jornada Basin LTER program began in 1982 at a Chihuahuan Desert site in southern New Mexico, where black grama-dominated (Bouteloua eriopoda) grasslands converted to shrublands following livestock overgrazing and drought. Early Jornada studies focused on the causes and consequences of this desertification. In collaboration with USDA scientists, the two LTER programs developed new research ideas and approaches which brought an improved understanding of historic dynamics and nuance to the Clementsian-based paradigm. New paradigms also reflected the importance of objective, long-term studies and the dynamic, multi-scale nature of these arid and semiarid ecosystems. Comparing two LTER programs at research sites sharing a conceptual basis, but with different ecosystem properties, can provide insights into the development of US grassland ecology over the past century.}, keywords = {arid ecosystems, desertification, drought, Ecological climax, grassland ecology, International Biological Program, livestock grazing, long-term ecological research, LTER program}, isbn = {978-3-030-66932-4}, doi = {10.1007/978-3-030-66933-1_6}, author = {Debra C. Peters} } @article {JRN55290, title = {Modifying connectivity to promote state change reversal: the importance of geomorphic context and plant{\textendash}soil feedbacks}, journal = {Ecology}, volume = {101}, year = {2020}, month = {4/16/2020}, pages = {e03069}, abstract = {Alternative states maintained by feedbacks are notoriously difficult, if not impossible, to reverse. Although positive interactions that modify soil conditions may have the greatest potential to alter self-reinforcing feedbacks, the conditions leading to these state change reversals have not been resolved. In a 9-yr study, we modified horizontal connectivity of resources by wind or water on different geomorphic surfaces in an attempt to alter plant{\textendash}soil feedbacks and shift woody-plant-dominated states back toward perennial grass dominance. Modifying connectivity resulted in an increase in litter cover regardless of the vector of transport (wind, water) followed by an increase in perennial grass cover 2 yr later. Modifying connectivity was most effective on sandy soils where wind is the dominant vector, and least effective on gravelly soils on stable surfaces with low sediment movement by water. We found that grass cover was related to precipitation in the first 5 yr of our study, and plant{\textendash}soil feedbacks developed following 6 yr of modified connectivity to overwhelm effects of precipitation on sandy, wind-blown soils. These feedbacks persisted through time under variable annual rainfall. On alluvial soils, either plant{\textendash}soil feedbacks developed after 7 yr that were not persistent (active soils) or did not develop (stable soils). This novel approach has application to drylands globally where desertified lands have suffered losses in ecosystem services, and to other ecosystems where connectivity-mediated feedbacks modified at fine scales can be expected to impact plant recovery and state change reversals at larger scales, in particular for wind-impacted sites.}, keywords = {aeolian processes, alternative states, cusp-catastrophe model, desertification, ecohydrology, long-term studies, regime shifts remediation}, doi = {10.1002/ecy.3069}, url = {files/bibliography/20-035.pdf}, author = {Debra C. Peters and Gregory S. Okin and Jeffrey E. Herrick and Heather Savoy and John P. Anderson and Stacey L P Scroggs and J. Zhang} } @article {JRN55184, title = {Herbivory Effects on Ephedra spp. in the Chihuahuan Desert}, journal = {Open Journal of Ecology}, volume = {10}, year = {2020}, month = { February 2020}, pages = { 37-44 }, abstract = {

Two species of Ephedra: E. trifurca and E. torreyana inhabit shrub and grassland habitats in the northern Chihuahuan Desert. E. torreyana is limited to black grama grasslands where grasses are taller than the shrub. E. torreyana is heavily browsed by vertebrates and E. trifurca is browsed during some years. We established an experiment with cylindrical exclosures that excluded rabbits and rodents, rabbits but accessible to rodents, for comparison with E. torreyana plants available to all herbivores. Plants accessible to all vertebrate herbivores were significantly smaller with shorter stem lengths than plants in exclosures. We concluded that E. torreyana in black grama grassland are largely hidden from vertebrate herbivores and that intense herbivory reflects the degraded state of the study site which makes the E. torreyana evergreen shrubs apparent to vertebrates.

}, keywords = {Desert Cottontail Rabbits (Sylvilagus auduboni), desertification, Ephedra torreyana, Ephedra trifurca, Exclosures, Jackrabbits (Lepus californicus)}, doi = {10.4236/oje.2020.102003}, url = {files/bibliography/20-007.pdf}, author = {Walter G. Whitford and Yosef Steinberger} } @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 {JRN54148, title = {Desertification, land use, and the transformation of global drylands}, journal = {Frontiers in Ecology and the Environment}, volume = {13}, year = {2015}, month = {02/2015}, pages = {28-36}, chapter = {28}, abstract = {

Desertification is an escalating concern in global drylands, yet assessments to guide management and policy responses are limited by ambiguity concerning the definition of {\textquotedblleft}desertification{\textquotedblright} and what processes are involved. To improve clarity, we propose that assessments of desertification and land transformation be placed within a state change{\textendash}land-use change (SC{\textendash}LUC) framework. This framework considers desertification as state changes occurring within the context of particular land uses (eg rangeland, cropland) that interact with land-use change. State changes that can be readily reversed are distinguished from regime shifts, which are state changes involving persistent alterations to vegetation or soil properties. Pressures driving the transformation of rangelands to other types of land uses may be low, fluctuating, or high, and may influence and be influenced by state change. We discuss how the SC{\textendash}LUC perspective can guide more effective assessment of desertification and management of drylands.

}, keywords = {desertification, land management, land use, land use change, SC-LUC, state change}, doi = {10.1890/140162}, url = {/files/bibliography/15-004.pdf}, author = {Brandon T Bestelmeyer and Gregory S. Okin and Danielle Duni and Steven R. Archer and N. F. Sayre and Jebediah C. Williamson and Jeffrey E. Herrick} } @article {JRN54143, title = {Beyond desertification: new paradigms for dryland landscapes}, journal = {Frontiers in Ecology and the Environment}, volume = {13}, year = {2015}, month = {02/2015}, pages = {4-12}, chapter = {4}, abstract = {

The traditional desertification paradigm focuses on the losses of ecosystem services that typically occur when grasslands transition to systems dominated by bare (unvegetated) ground or by woody plants that are unpalatable to domestic livestock. However, recent studies reveal complex transitions across a range of environmental conditions and socioeconomic contexts. The papers in this Special Issue illustrate how an improved understanding of these dynamics is generating more robust paradigms, where state changes and regime shifts occurring within the context of changes in land use and climate are modified by landform and antecedent conditions. New and emerging technologies are being used to characterize and evaluate processes and outcomes across various scales and levels of organization. At the same time, developments in education are taking advantage of these new perspectives to improve the ecological literacy of future generations, and to better inform land-management decisions. A framework that integrates these perspectives provides a more comprehensive approach for understanding and predicting dryland dynamics.

}, keywords = {desertification, desertification paradigm, dryland landscapes, ecological literacy, ecosystem services, land management, land use, regime shifts, spatial connectivity}, doi = {10.1890/140276}, url = {/files/bibliography/15-001.pdf}, author = {Debra C. Peters and Kris Havstad and Steven R. Archer and O. E. Sala} } @article {JRN54189, title = {Modifying landscape connectivity by reducing wind driven sediment redistribution, northern Chihuahuan Desert, USA}, journal = {Aeolian Research}, volume = {17}, year = {2015}, month = {06/2015}, pages = {129-137}, chapter = {129}, abstract = {

Shrub encroachment into perennial grasslands is occurring in many arid parts of the world. As shrubs displace perennial grasslands, bare patches can coalesce creating sediment transport pathways that further enhance sediment fluxes by wind transport. Reducing the connectedness of these pathways could slow or stop grassland loss by limiting sediment redistribution. To test this hypothesis, sediment retention structures, hereafter called {\textquotedblleft}Connectivity Modifiers{\textquotedblright} (Con-Mods), were placed in bare gaps of existing shrublands to block sediment movement by wind transport on two sites: the basin floor and a bajada (i.e. piedmont slope) at the Jornada Basin LTER in southern New Mexico. Wind blown sediment collectors and short-lived radionuclides (210Pbex, 137Cs, and 7Be) were used to determine if these structures are affecting seasonal aeolian sediment transport within bare gaps. Net sediment flux rates at 10\ cm height indicate a loss of 2.5{\textendash}14.2\ g\ m-2\ d-1 for both sites for the monsoon season (Jul{\textendash}Nov), while the basin floor site was the most responsive in reducing sediment transport by collecting 16.5\ g\ m-2\ d-1 over the windy season (Dec{\textendash}May). Con-Mods contained 30{\textendash}50\% higher surface radionuclide activities than the control plots for both transport seasons on the basin floor. However, there was no detectible difference between surface concentrations for the structures and controls seasonally on the bajada site. This study demonstrates that changes in connectivity can influence sediment movement. Altering sediment transport through bare gaps could influence ecosystem state changes in arid systems; thereby increasing the likelihood of recruitment of native plants.

}, keywords = {aeolian transport, connectivity, desertification, sediment redistribution, short lived radionuclides, shrub encroachment}, doi = {10.1016/j.aeolia.2015.03.003}, url = {/files/bibliography/15-011.pdf}, author = {Rachal, David M. and Gregory S. Okin and Charles E. Alexander and Jeffrey E. Herrick and Debra C. Peters} } @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 {JRN53910, title = {Savory{\textquoteright}s unsubstantiated claims should not be confused with multipaddock grazing}, journal = {Rangelands}, volume = {36}, year = {2014}, month = {02/2014}, pages = {39-42}, type = {Letter to the Editor}, chapter = {39}, abstract = {

Letters to the Editor: The sole objective of our critique of Mr Savory{\textquoteright}s TED video published in Rangelands1 was to {\textquotedblleft}fact check{\textquotedblright} a portion of the extraordinary claims that he had made relative to sciencebased information. It is incumbent upon a professional discipline to evaluate the relevant evidence and potential viability of proposed management strategies and policies. Regrettably, Richard Teague{\textquoteright}s response does not address any of Mr Savory{\textquoteright}s claims that we addressed in our critique{\textemdash}not all global rangelands are degraded, rangelands have a limited capacity to store carbon, and intensive rotational grazing is not necessary to prevent rangelands from degrading. Here we reiterate these last two points of our initial critique, then address the concerns presented by Teague, and conclude with comments regarding the future direction of grazing systems research.

}, keywords = {climate change, desertification, planned grazing, Savory Method}, doi = {10.2111/1551-501X-36.1.39 }, url = {/files/bibliography/14-008.pdf}, author = {D.D. Briske and Brandon T Bestelmeyer and Joel R. Brown} } @article {JRN53911, title = {Constraints and time lags for recovery of a keystone species (Dipodomys spectabilis) after landscape restoration}, journal = {Landscape Ecology}, volume = {29}, year = {2014}, month = {02/2014}, pages = {665-675}, chapter = {665}, abstract = {

Habitat restoration is typically focused on reestablishing suitable conditions at a local scale, but landscape constraints may be important for keystone species with limited dispersal. We tested for time lags and examined the relative importance of local and landscape constraints on the response of the banner-tailed kangaroo rat (Dipodomys spectabilis) to restoration of Chihuahuan Desert grasslands in New Mexico, USA. Dipodomys spectabilis is a keystone species that creates habitat heterogeneity and modifies the structure of plant and animal communities. We selected 21 sites and compared density of D. spectabilis between areas treated with herbicide to control shrubs (treated areas) and paired untreated areas. We evaluated whether density of D. spectabilis depended on treatment age, local habitat quality (vegetation and soil structure), and landscape factors (treatment area and spatial connectivity). Density was greater at treated areas than at untreated areas due to a direct effect of reduced shrub cover. However, the response of D. spectabilis to restoration was lagged by a decade or more. Structural equation modeling indicated the time lag reflected a dispersal constraint as opposed to a temporal change in habitat quality. This inference was corroborated by a positive relationship between density at treated areas and connectivity to source populations. Our results indicate that density of D. spectabilis depended strongly on the spatial configuration of treated areas, which supports a landscape mosaic approach to restoration. If keystone species commonly exhibit limited dispersal ability, landscape constraints may be broadly important for shaping ecosystem structure and function after habitat restoration.

}, keywords = {colonization, connectivity, conservation, desertification, Dipodomys spectabilis, dispersal, ecosystem engineer, grassland, kangaroo rat, shrub encroachment}, doi = {10.1007/s10980-014-0003-5}, url = {/files/bibliography/14-007.pdf}, author = {Brad Cosentino and Robert L. Schooley and Brandon T Bestelmeyer and J.F. Kelly and John M. Coffman} } @article {49838, title = {A test of critical thresholds and their indicators in a desertification-prone ecosystem: more resilience than we thought}, journal = {Ecology Letters}, volume = {16}, year = {2013}, month = {01/2013}, pages = {339-345}, chapter = {339}, abstract = {

Theoretical models predict that drylands can cross critical thresholds, but experimental manipulations to evaluate them are non-existent. We used a long-term (13-year) pulse-perturbation experiment featuring heavy grazing and shrub removal to determine if critical thresholds and their determinants can be demonstrated in Chihuahuan Desert grasslands. We asked if cover values or patch-size metrics could predict vegetation recovery, supporting their use as early-warning indicators. We found that season of grazing, but not the presence of competing shrubs, mediated the severity of grazing impacts on dominant grasses. Recovery occurred at the same rate irrespective of grazing history, suggesting that critical thresholds were not crossed, even at low cover levels. Grass cover, but not patch size metrics, predicted variation in recovery rates. Some transition-prone ecosystems are surprisingly resilient; management of grazing impacts and simple cover measurements can be used to avert undesired transitions and initiate restoration.

}, keywords = {desertification, early warning, grazing, long-term experiment, patch size, regime shift, resilience, state-transition model}, doi = {10.1111/ele.12045}, url = {/files/bibliography/13-005.pdf}, author = {Brandon T Bestelmeyer and Danielle Duni and D. K. James and Laura M. Burkett and Kris Havstad} } @article {49839, title = {The Savory Method can not green deserts or reverse climate change}, journal = {Rangelands}, volume = {35}, year = {2013}, pages = {72-74}, abstract = {

This is a refutation of Allan Savory claims that his "planned grazing" method was necessary to reverse desertification and climate change as presented in the video "How to green the world{\textquoteright}s deserts and reverse climate change" that was presented in session 7 at the 2013 TED (Technology, Entertainment, Design) Conference on 27 February 2013 in Long Beach, California.

Allan Savory stated that his {\textquotedblleft}planned grazing{\textquotedblright} method was necessary to reverse two of the world{\textquoteright}s most challenging and interlinked global change processes{\textemdash}desertification and climate change{\textemdash}in the video {\textquotedblleft}How to green the world{\textquoteright}s deserts and reverse climate change{\textquotedblright} that was presented in session 7 at the 2013 TED (Technology, Entertainment, Design) Conference on 27 February 2013 in Long Beach, California.i As members of the scientific community, it is our obligation to evaluate the claims made in this video relative to the existing scientific information on this topic.

We find all of Mr Savory{\textquoteright}s major claims to be unfounded and we express deep concern that they have the potential to undermine proven, practical approaches to rangeland management and restoration that are supported by a global community of practitioners and scientists. The two major assumptions underlying Mr Savory{\textquoteright}s presentation are alone sufficient grounds for extreme skepticism. First is that humans have misunderstood the basic grassland{\textendash}grazer relationships for centuries and that only he knows the true nature of this relationship. Second is that use of intensive, concentrated livestock grazing, specific to the method that Mr Savory developed, is the only viable solution to reverse desertification and climate change. In addition to challenging these two highly problematic assumptions, we present a spe-cific critique of three invalid arguments that Mr Savory used to claim that his grazing method can reverse desertification, climate change, and alleviate human suffering and death (19:00 in video).

}, keywords = {climate change, desertification, planned grazing}, doi = {10.2111/RANGELANDS-D-13-00044.1}, url = {/files/bibliography/13-034.pdf}, author = {D.D. Briske and Brandon T Bestelmeyer and Joel R. Brown and S. Fuhlendorf and Polley, H. Wayne} } @article {49845, title = {Response of lizard community structure to desert grassland restoration mediated by a keystone rodent}, journal = {Biodiversity and Conservation Journal}, volume = {22}, year = {2013}, month = {02/2013}, pages = {921-935}, chapter = {921}, abstract = {

Many grasslands in the Chihuahuan Desert have transformed to shrublands dominated by creosotebush (Larrea tridentata). Grassland restoration efforts have been directed at controlling creosotebush by applying herbicide over large spatial scales. However, we have a limited understanding of how landscape-scale restoration affects biodiversity. We examined whether restoration treatments in southern New Mexico, USA have influenced the community structure of lizards, which are sensitive to shrub encroachment. We compared lizard community structure on 21 sites treated with herbicide from 7-29 years ago with paired references matched by geomorphology, soils, and elevation. To examine mechanisms underlying responses to restoration, we tested whether the abundance of a grassland specialist, Aspidoscelis uniparens, depended on time since treatment, treatment area and isolation, and local habitat quality. Because lizards use rodent burrows as habitat, we tested whether community structure and A. uniparens abundance depended on the abundance of the keystone rodent, Dipodomys spectabilis. Treatments had reduced shrub cover and increased grass cover compared to references. Lizard community composition differed strongly between plots, with four species responding to treatments. Divergence in community composition between treatment-reference pairs was greatest for old treatments (=22 years), and community composition was influenced by D. spectabilis. In particular, the abundance of A. uniparens was greatest on old treatments with a high density of D. spectabilis. Overall, our results demonstrate lizard community structure responds to grassland restoration efforts, and keystone species can shape restoration responses. Reestablishment of keystone species may be a critical constraint on the recovery of animal biodiversity after habitat restoration.

}, keywords = {Aspidoscelis spp., desertification, Dipodomys spectabilis, grassland restoration, keystone species, shrub encroachment}, doi = {10.1007/s10531-013-0459-7}, url = {/files/bibliography/13-021.pdf}, author = {Brad Cosentino and Robert L. Schooley and Brandon T Bestelmeyer and John M. Coffman} } @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.} } @inbook {49858, title = {Desertification of Rangelands}, booktitle = {Climate Vulnerability: Understanding and Addressing Threats to Essential Resources}, series = {Climate Vulnerability}, volume = {4}, number = {4}, year = {2013}, pages = {239-258}, publisher = {Academic Press}, organization = {Academic Press}, edition = {First}, abstract = {Desertification, the broad-scale conversion of perennial grasslands to dominance by xerophytic shrubs, and the attendant consequences to ecosystem services has affected arid and semiarid regions globally over the past several centuries. This state change is expected to continue in the future as environmental drivers continue to change. It is generally well-recognized that desertification is a cumulative threat that explicitly includes both climatic (e.g., drought) and land-use drivers (e.g., livestock overgrazing and inappropriate conversions of rangeland to cropland).\  However, a basis for ranking the relative importance of these drivers is lacking for many locations. In addition, the emergence of additional drivers (e.g., non-native forbs and grasses modifying historic fire regimes), will result in even more complex dynamics in the future. Clearly, directional changes in climate can have unanticipated effects, in particular for dryland regions with low and variable precipitation and high temperatures in the growing season. However, any change in climate will be operating across diverse landscapes that include a mosaic of human-dominated and natural states, each governed by different drivers and susceptible to different threats. Accounting for the separate and interactive effects of these threats on grassland-shrubland transitions will be necessary as we move forward into a difficult to predict, if not unknown, environmental world.}, keywords = {biodiversity, climate, desertification, dryland ecosystems, feedbacks, grasslands, invasive species, land management, land use, land-atmosphere interactions, shrublands, state change, thresholds, water, wind}, doi = {10.1016/B978-0-12-384703-4.00426-3}, url = {/files/bibliography/13-014.pdf}, author = {Debra C. Peters and Steven R. Archer and Brandon T Bestelmeyer and Brooks, Andrew and Joel R. Brown and Comrie, Andrew and Gimblett, H. Randy and Goldstein, Joshua H. and Kris Havstad and Lopez-Hoffman, L. and Curtis H. Monger and Gregory S. Okin and A. Rango and O. E. Sala and Craig Tweedie and Enrique Vivoni} } @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 {49994, title = {Experiences in monitoring and assessment of sustainable land management}, journal = {Land Degradation and Development}, volume = {22}, year = {2011}, month = {04/2011}, pages = {214-225}, chapter = {214}, abstract = {

Although sustainable land management (SLM) is widely promoted to prevent and mitigate land degradation and desertification, its monitoring and assessment (M\&A) has received much less attention. This paper compiles methodological approaches which to date have been little reported in the literature. It draws lessons from these experiences and identifies common elements and future pathways as a basis for a global approach. The paper starts with local level methods where the World Overview of Conservation Approaches and Technologies (WOCAT) framework catalogues SLM case studies. This tool has been included in the local level assessment of Land Degradation Assessment in Drylands (LADA) and in the EU-DESIRE project. Complementary site-based approaches can enhance an ecological process-based understanding of SLM variation. At national and sub-national levels, a joint WOCAT/LADA/DESIRE spatial assessment based on land use systems identifies the status and trends of degradation and SLM, including causes, drivers and impacts on ecosystem services. Expert consultation is combined with scientific evidence and enhanced where necessary with secondary data and indicator databases. At the global level, the Global Environment Facility (GEF) knowledge from the land (KM:Land) initiative uses indicators to demonstrate impacts of SLM investments. Key lessons learnt include the need for a multi-scale approach, making use of common indicators and a variety of information sources, including scientific data and local knowledge through participatory methods. Methodological consistencies allow cross-scale analyses, and findings are analysed and documented for use by decision-makers at various levels. Effective M\&A of SLM [e.g. for United Nations Convention to Combat Desertification (UNCCD)] requires a comprehensive methodological framework agreed by the major players.

}, keywords = {desertification, impact assessment, methodological framework, monitoring, multiple scales, participatory approaches, sustainable land management}, doi = {10.1002/ldr.1040}, url = {/files/bibliography/11-039.pdf}, author = {Schwilch, G. and Brandon T Bestelmeyer and Bunning, S. and Critchley, W. and Jeffrey E. Herrick and Kellner, K. and H. Liniger and Nachtergaele, F. and Ritsema, C. J. and Schuster, B. and Tabo, R. and Van Lynden, G. and Winslow, M.} } @conference {50089, title = {Multiscale variability of soil aggregate stability: implications for rangeland hydrology and erosion}, booktitle = {62nd Society for Range Mangement Annual Meeting}, year = {2009}, month = {February 8-12, 2}, pages = {07-11}, publisher = {Society for Range Management}, organization = {Society for Range Management}, address = {Alb., NM}, abstract = {Conservation of soil and water resources in rangelands is a crucial step in stopping desertification processes. The formation of water-stable soil aggregates reduces soil erodibility and can increase infiltration capacity in many soils. Soil aggregate stability is highly variable at scales ranging from individual aggregates to bioclimatic regions due to complex interactions of soil texture, soil organic matter, soil organisms, vegetation and surface disturbance. Variability in soil aggregate stability at all scales has important implications for rangeland hydrology and erosion. We conducted field soil aggregate stability tests at multiple scales (plot, landscape, and regional) throughout the western United States and in areas with varying degrees of vehicle-related disturbances. Additionally, small plot scale rainfall simulation experiments were conducted in conjunction with soil stability measures. Results demonstrate the scale-dependent nature of variability in soil aggregate stability, particularly within a disturbance gradient. The implications of this variability for hydrology and erosion are explored by contrasting variability in soil stability among scales, disturbance types and regions. Other site properties related to hydrology and erosion, including soil texture, vegetation, and cover and distribution bareground, are used to highlight possible mechanisms. In rangeland monitoring and assessment activities, the application of average soil stability values over large areas can be appropriate. Soil degradation at small scales, however, can result in disproportionally large increases in soil erosion and run-off. Results from our studies and related literature indicate that large variability occurring at relatively small scales should be considered for multi-scale estimates of changes in rangeland hydrology and erosion.}, keywords = {aggregate, desertification, hydrology, stability}, author = {Danielle Duni and Jeffrey E. Herrick and K. Spaeth and N. Barger and Justin Van Zee and Jayne Belnap} } @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 {50107, title = {Can kangaroo rat graminivory contribute to the persistence of desertified shrublands?}, journal = {Journal of Arid Environments}, volume = {73}, year = {2009}, pages = {651-657}, abstract = {

Medium-sized kangaroo rats (Dipodomys spp. Gray) function as keystone species in the dynamics of desert bunchgrasses. We tested the hypothesis that kangaroo rat graminivory leads to reduced grass growth and inflorescence production, and that kangaroo rat grass consumption reflects their preferences for open microhabitats. We excluded kangaroo rats from grasses, and measured tiller loss, leaf and tiller growth and inflorescence production. We recorded the extent of tiller loss in grasses varying in tussock size or the extent of surrounding cover. Consumption of tillers by kangaroo rats was extensive, peaking in late summer. Grasses protected from kangaroo rat graminivory showed elevated leaf and tiller growth and inflorescence production. Grass tussocks protected by surrounding vegetation or large grass tussocks suffered lower graminivory than tussocks in the open or small tussocks. Our data demonstrate that the mechanism of the keystone role of kangaroo rats is through direct graminivory. We hypothesize that kangaroo rat graminivory may contribute to the persistence of desertified shrublands by limiting grass recruitment and abundance. Medium-sized kangaroo rats prefer open microhabitats and increase in abundance as such microhabitats increase, suggesting a positive feedback, with kangaroo rats increasing in abundance in overgrazed, desertified landscapes, and then contributing to their persistence through graminivory. {\textcopyright} 2009 Elsevier Ltd. All rights reserved

}, keywords = {desert bunch grasses, desertification, Dipodomys merriami, Dipodomys ordii, Eragrostis lehmanniana, graminivory, kangaroo rat, keystone species, patch use, positive feedback, small mammals, Sporobolus flexuosus}, doi = {10.1016/j.jaridenv.2009.01.001}, url = {files/bibliography/JRN00524.pdf}, author = {G. I. H. Kerley and Walter G. Whitford} } @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 {50140, title = {Small mammal herbivory: Feedbacks that help maintain desertified ecosystems}, journal = {Journal of Arid Environments}, volume = {73}, number = {73}, year = {2009}, month = {01/2009}, pages = {62-65}, chapter = {62}, abstract = {

We tested the hypothesis that herbivores contribute to feedbacks maintaining arid ecosystems in a degraded state. We studied small mammal herbivory on a subshrub, broom snakeweed (Gutierrezia sarothrae), and perennial grasses at three sites: (1) ungrazed black grama (Bouteloua eriopoda) grassland; (2) grassland degraded by intense short-duration grazing; and (3) mesquite (Prosopis glandulosa) coppice dunes. Snakeweed was browsed by herbivores primarily during dry winter months. The average percent of G. sarothrae standing crop biomass removed by browsing was 9.2 in ungrazed grassland, 7.4 in intensely grazed grassland, and 4.1 in the dunes. In ungrazed grassland, an average of 12\% of grass cover was harvested by herbivores; in the intensely grazed plots \– 80\%. Herbivore exclusion plots showed that jackrabbits (Lepus californicus) were the primary browsers on snakeweed and rodents on grasses and G. sarothrae inflorescences. Rodent removal of G. sarothrae inflorescences allows wind dispersal of seeds in disturbed and desertified areas, thereby increasing abundance of this poisonous shrub. Grass-tiller cutting by rodents provides a strong feedback that may be responsible for keeping the grass cover low on the intensely grazed areas. Jackrabbit pruning has little effect on G. sarothrae abundance at any stage of desertification.

}, keywords = {browsing, desertification, herbivory, jackrabbit, livestock grazing, snakeweed}, doi = {10.1016/j.jaridenv.2008.09.003}, url = {/files/bibliography/09-001.pdf}, author = {Roth, G.A. and Walter G. Whitford and Yosef Steinberger} } @article {50247, title = {Spatial variability of soil and nutrient characteristics of semi-arid grasslands and shrublands, Jornada Basin, New Mexico}, journal = {Ecohydrology}, volume = {1}, year = {2008}, note = {//USDA//LTER-V//entered 06/02/2008; PDF on file}, month = {2008}, pages = {3-12}, abstract = {

Heterogeneity of vegetation and soil properties is characteristic of semi-arid and arid environments. The potential underlying causes of the dynamics that create this spatial variability, with consequent impacts on landscape connectivity and thus ecological and ecohydrological processes, are not clearly understood. An investigation was carried out into the spatial variability of ponded infiltration rate, soil moisture, soil-aggregate stability, vegetation cover, random roughness and nutrient content in the soil (ammonium, nitrate and phosphorus) at grassland and shrubland sites for two spatial scales in the Jornada Basin, in the northern part of the Chihuahua desert. At the plant-interplant scale, statistically significant differences exist between vegetated and non-vegetated sites for soil moisture and infiltration rate within both shrublands and grasslands. The spatial distributions of all other parameters follow a more complex scheme at this scale. At the landscape scale, distinct differences exist for most parameters between the grasslands and the shrubland sites. Geostatistical analysis revealed that the autocorrelation lengths are not simply a function of average shrub sizes, but may be caused by a more complex pattern probably related to the spatial layout of rill and inter-rill areas and other localized transfers of soil resources through the redistribution of water and wind. These results demonstrate the importance of understanding spatial linkages of processes within the landscape in understanding dryland ecosystem dynamics. Copyright {\textcopyright} 2007 John Wiley \& Sons, Ltd.

}, keywords = {article, connectivity, desert ecosystems, desertification, grassland, hydrology, Jornada, Jornada Basin, journal, landscape ecology, shrubland, soil characteristics, spatial variability, soil nutrients, spatial variability, spatial variability}, doi = {10.1002/eco.1}, url = {files/bibliography/JRN00515.pdf}, author = {Eva N. M{\"u}ller and John Wainwright and A.J. Parsons} } @inbook {50278, title = {Land resources: forests and arid lands}, booktitle = {The effects of climate change on agriculture, land resources, water resources, and biodiversity in the United States.}, series = {Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research}, number = {Synthesis and Assessment Product 4.3.}, year = {2008}, note = {//USDA//LTER V//entered 05/29/2008; PDF availableProCite field[6]: InProCite field[8]: Convening lead authorsProCite field[31]: Managing editor}, month = {2008}, pages = {362 pp.}, address = {Washington, DC., USA}, abstract = {

This synthesis and assessment report builds on an extensive scientific literature and series of recent assessments of the historical and potential impacts of climate change and climate variability on managed and unmanaged ecosystems and their constituent biota and processes. It identifies changes in resource conditions that are now being observed and examines whether these changes can be attributed in whole or part to climate change. It also highlights changes in resource conditions that recent scientific studies suggest are most likely to occur in response to climate change, and when and where to look for these changes. As outlined in the Climate Change Science Program (CCSP) Synthesis and Assessment Product 4.3 (SAP 4.3) prospectus, this chapter will specifically address climate-related issues in forests and arid lands.In this chapter the focus is on the near-term future. In some cases, key results are reported out to 100 years to provide a larger context but the emphasis is on next 25-50 years. This nearer-term focus is chosen for two reasons. First, for many natural resources, planning and management activities already address these time scales through development of long-lived infrastructure, forest rotations, and other significant investments. Second, climate projections are relatively certain over the next few decades. Emission scenarios for the next few decades do not diverge from each other significantly because of the {\textquotedblleft}inertia{\textquotedblright} of the energy system. Most projections of greenhouse gas emissions assume that it will take decades to make major changes in the energy infrastructure, and only begin to diverge rapidly after several decades have passed (30-50 years).

}, keywords = {arid lands, book, chapter, climate change, desertification, report}, url = {files/bibliography/JRN00504.pdf}, author = {Ryan, M. G. and Steven R. Archer and Birdsey, R. and Dahm, C. and Heath, L. and Hicke, J. and Hollinger, D. and T. Huxman and Gregory S. Okin and Oren, R. and J. Randerson and W. H. Schlesinger}, editor = {Backlund, Peter and Janetos, Anthony and David Schimel} } @article {50314, title = {Multiscale variability in soil aggregate stability: Implications for understanding semiarid grassland degradation}, journal = {Geoderma}, volume = {140}, year = {2007}, month = {04/2007}, pages = {106-118}, abstract = {Grassland degradation typifies desertification in many regions of the world. Changes in plant communities and increased soil resource loss and redistribution have been widely documented in degrading grasslands. Increased soil loss and redistribution are commonly associated with changes in soil structure, yet variability in soil structure in arid ecosystems has been little studied. We compared soil aggregate stability in a Chihuahuan Desert grassland at the plant and landscape scales by assessing aggregate stability at four sites in two cover classes (under grass canopy vs. in bare interspace) located within each of three grass cover and land disturbance classes. Soil aggregate stability is a key indicator of soil structure and is correlated with erodibility and water infiltration capacity. To increase measurement sensitivity to changes in soil structure and identify potential early warning indicators for monitoring, we used two different methods for quantifying wet aggregate stability: stability of aggregates \> 0.25 mm was assessed in the laboratory and that of 1.5 mm aggregates was assessed in the field. As expected, soil aggregate stability was significantly higher under grass plants than in plant interspaces (44.2 vs. 38.4\% for the lab test and 4.4 vs. 3.3 stability class for the field test; p \< 0.01). This plant-interspace pattern was consistent at all four study sites, but the absolute values for under plants and in interspaces varied across the landscape. The field test showed higher stability throughout the top 10 cm in plots with higher grass cover throughout the top 10 cm, while disturbance level only affected stability at the soil surface. The laboratory test was insensitive to differences in grass cover and disturbance. High variability at the plant-interspace scale supports earlier work on biogeochemistry, reflecting linkages between the spatial distribution of soil structure, soil organic matter, and nutrient cycling. The established relationship between soil aggregate stability and other soil properties and processes, the relative sensitivity of the field test, and lack of sensitivity of the lab test to differences in grass cover and disturbance support the use of the field test as an indicator for managing both grass cover and soil surface disturbance in arid grasslands. http://www.sciencedirect.com/science/article/pii/S0016706107000912}, keywords = {desertification, grassland degradation, soil aggregate, soil structure, stability, variability}, doi = {10.1016/j.geoderma.2007.03.010}, url = {/files/bibliography/07-017.pdf}, author = {S.B. Bird and Jeffrey E. Herrick and Wander, M.M. and L. W. Murray} } @conference {50321, title = {Complexity in rodent community respones to grassland-shrubland trasititions}, booktitle = {87th Annual Meeting American Society of Mammalogist}, year = {2007}, month = {June 6-8, 2007}, pages = {p. 89}, address = {Albuquerque, NM}, 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 a suite of biotic-abiotic interactions may influence rodent population responses to spatial variation in habitat in complex ways, mediating the general habitat/abundance relationship. The consistency of rodent responses to shrub encroachment across a landscape and over time has not been examined in the past and is the objective of this study. Between 2002 and 2006 we monitored rodent populations on five grassland-shrubland ecotone sites in the Jornada Basin (NM, USA). The ecotones are within the same vegetation types and soils (Bouteloua eriopoda and Prosopis glandulosa on coarse loamy Argids), but they are dynamic (with shrubs expanding into grasslands over the last century) and varied in total shrub and grass abundance depending on mesoclimate and disturbance history. We also monitored 23 additional grids distributed across an area of 200 square kilometers and ranging from healthy grasslands to dense mesquite dunes. Precipitation at all sites was recorded. We tested the hypothesis that rodent richness, biomass, and density/abundance were highest in shrub-dominated portions of replicate grassland-shrubland ecotones and across grassland-shrubland transitions. We found that overall rodent richness, biomass and abundance were highly variable across the landscape and responses to shrub cover and precipitation were not always linear across years. Perennial grass cover and bare ground cover did not show significant effects on rodent populations. We conclude that absolute differences in shrub cover across the landscape are more important than relative differences in vegetation structure (i.e. shrub cover) within an ecotone for aggregate measures of rodent communities.}, keywords = {abiotic, biotic, desertification, diversity, rodents}, author = {A. Campanella and Brandon T Bestelmeyer and G. Roemer and Debra C. Peters} } @article {50363, title = {The stability of vegetation boundaries and the propagation of desertification in the American Southwest: a modelling approach}, journal = {Ecological Modelling}, volume = {208}, year = {2007}, note = {//NMSU, USDA//LTER-V//entered 08/15/2007; updated 11/20/2007}, month = {2007}, pages = {91-101}, abstract = {

A process-based approach to spatially distributed, overland-flow modelling is employed to assess the impact of water and nutrient redistribution at the landscape scale caused by short, high-intensity rainstorm events across grassland{\textendash}shrubland vegetation boundaries of a semi-arid ecosystem in the south-western United States. The modelling scenarios showed that simulated fluxes from shrubland into grassland lead to a gain of water resources but to a loss of nutrient resources in the grassland areas close to the boundary. Simulated fluxes from grasslands into shrublands do not lead to a gain of water resources, but to an increase of nutrient resources for the shrubland areas close to the boundary. On the basis of the modelling results, a new hypothesis for the on-going desertification process in the southwestern United States is proposed. It is hypothesised that a vegetation boundary is stable when two conditions prevail to balance the lower resistance of grassland within the existing environmental setting with the higher resistance of shrubland: that the depletion of soil nutrients by the action of overland flow in the grassland zone close to the boundary is in balance with the replenishment rates of grassland by other nutrient cycling, and that the grassland gains enough water resources from the upslope shrublands. In contrast, a vegetation boundary potentially becomes unstable when the grassland acquires a competitive disadvantage towards shrubland regarding water benefit and nutrient depletion due to the combined effects of overland-flow dynamics and some external forces such as extensive overgrazing or climate change. The modelling results suggest that landscape linkages through the redistribution of water and soil resources across vegetation-transition zones at the landscape scale and feedback dynamics of overland-flow processes play a significant role in the persistence of land degradation in the US Southwest. {\textcopyright} 2007 Elsevier B.V. All rights reserved.

}, keywords = {article, desertification, hydrology, connectivity, hydrology, ecotones, hydrology, grassland, hydrology, model, hydrology, nutrient resources, hydrology, shrubland, journal, model, desertification, model, overland flow, model, vegetation boundaries, vegetation boundaries}, doi = {10.1016/j.ecolmodel.2007.04.010}, url = {files/bibliography/JRN00486.pdf}, author = {Eva N. M{\"u}ller and John Wainwright and A.J. Parsons} } @inbook {50371, title = {Spatial nonlinearities: Cascading effects in the earth system}, booktitle = {Terrestrial Ecosystems in a Changing World}, year = {2007}, month = {2007}, pages = {165-174}, publisher = {Springer Verlag}, organization = {Springer Verlag}, address = {Berlin, Germany}, abstract = {Nonlinear interactions and feedbacks associated with thresholds through time and across space are common features of biological, physical and materials systems. These spatial nonlinearities generate surprising behavior where dynamics at one scale cannot be easily predicted based on information obtained at finer or broader scales. These cascading effects often result in severe consequences for the environment and human welfare (i.e., catastrophes) that are expected to be particularly important under conditions of changes in climate and land use. In this chapter, we illustrate the usefulness of a general conceptual and mathematical framework for understanding and forecasting spatially nonlinear responses to global change. This framework includes cross-scale interactions, threshold behavior and feedback mechanisms. We focus on spatial nonlinearities produced by fine-scale processes that cascade through time and across space to influence broad spatial extents. Here we describe the spread of catastrophic events in the context of our cross-disciplinary framework using examples from biology (wildfires, desertification, infectious diseases) and engineering (structural failures) and discuss the consequences of applying these ideas to forecasting future dynamics under a changing global environment.}, keywords = {desertification, nonlinearities, wildfires}, author = {Debra C. Peters and R.A. Pielke and Brandon T Bestelmeyer and C.D. Allen and Seth M. Munson and Kris Havstad}, editor = {J. Canadell and D.E. Pataki and Pitelka, L.} } @article {50376, title = {Global desertification: building a science for dryland development}, journal = {Science}, volume = {316}, year = {2007}, note = {//??//LTER-V//entered 08/15/2007}, month = {2007}, pages = {847-851}, abstract = {

In this millennium, global drylands face a myriad of problems that present tough research, management, and policy challenges. Recent advances in dryland development, however, together with the integrative approaches of global change and sustainability science, suggest that concerns about land degradation, poverty, safeguarding biodiversity, and protecting the culture of 2.5 billion people can be confronted with renewed optimism. We review recent lessons about the functioning of dryland ecosystems and the livelihood systems of their human residents and introduce a new synthetic framework, the Drylands Development Paradigm (DDP). The DDP, supported by a growing and well-documented set of tools for policy and management action, helps navigate the inherent complexity of desertification and dryland development, identifying and synthesizing those factors important to research, management, and policy communities.

}, keywords = {DDP, degradation, desertification, development, Drylands Development Paradigm, global}, doi = {10.1126/science.1131634 }, url = {/files/bibliography/07-012.pdf}, author = {J. F. Reynolds and D. Mark Stafford Smith and E. Lambin and B.L. Turner II and Mortimore, Michael and Batterbury, Simon P.J. and Downing, Thomas E. and Dowlatabadi, Hadi and Roberto J. Fern{\'a}ndez and Jeffrey E. Herrick and E. Huber-Sannwald and Jiang, Hong and Leemans, Rik and Lynam, Tim and F. Maestre and M. Ayarza and Brian Walker} } @article {50439, title = {Introduction to special issue - Landscape linkages and cross scale interactions in arid and semiarid ecosystems}, journal = {Journal of Arid Environments}, volume = {65}, year = {2006}, month = {April 2006}, pages = {193-195}, abstract = {The conversion of grasslands to shrublands in arid and semiarid ecosystems is a serious global problem. Although a great deal of research has been conducted on these conversions, we lack a complete understanding of the processes underlying the transitions. More importantly, our ability to predict when and where desertification will occur and our ability to manage landscapes to prevent degradation and restore degraded landscapes is limited. Research being conducted at the Jornada Experimental Range (JER) is addressing these problems in a new, synthetic way. Since 1981, scientists affiliated with the Jornada Basin Long-Term Ecological Research site in collaboration with scientists from the JER and New Mexico State University generated a number of new ideas and concepts regarding the processes governing desertification that changed our thinking about how these systems operate. Our focus now emphasizes cross-scale spatial and temporal heterogeneity in vegetation patterns and dynamics that have been difficult to explain using traditional approaches. The realization that our current knowledge often cannot explain the existing variability among land units led to the development of a conceptual model by JER scientists that considers nonlinear dynamics and connections among land units across scales. This cross-scale landscape ecology approach will further our understanding of critical processes occurring in arid regions globally and will provide insight to help identify mechanisms to address the pressing issue of desertification.}, keywords = {arid, cross scale, desertification, ecosystems, invasion, landscape, linkages, semiarid, shrub}, doi = {10.1016/j.jaridenv.2005.04.001}, url = {/files/bibliography/06-006.pdf}, author = {Richard E. Estell and E.L. Fredrickson and Debra C. Peters} } @conference {50464, title = {A case study of desertification linking biophysical and socioeconomic aspects fo water use in the small Mexican village of Amapola}, booktitle = {Global Environmental Change: Regional Challenges. An Earth System Science Partnership, Open Science Conference}, year = {2006}, month = {November 9-12, 2}, pages = {660}, address = {Beijing, China}, abstract = {Desertification is a major global environmental problem of human societies in drylands and Mexico is one of the most severely affected countries in the Americas. An assessment of how hydrological, ecological, meteorological and socioeconomic processes simultaneously affect, and are affected by, land degradation is one of the most challenging issues in global change research. In June 2004, the ARIDnet network convened an interdisciplinary workshop in Mexico to apply a new conceptual framework {\textendash} the Dahlem Desertification Paradigm (DDP) {\textendash} to La Amapola, a small rural community in the Central Plateau of Mexico. The DDP focuses on the interrelationships within coupled human-environment systems that cause desertification. We provide an overview of land degradation issues in La Amapola and highlight links between the hydrological cycle and desertification by considering the interacting roles of biophysical and socioeconomic factors. We present a conceptual model emphasizing linkages between biophysical and socioeconomic factors in La Amapola in the context of hydrology and land degradation. We discuss our findings derived from the application of the major DDP assertions. Numerous cross-scale feedbacks, linkages, and causal pathways within and between the biophysical and human dimensions support the critical importance of water allocation in support of multiple and often competing ecosystem services. The livelihoods of rural communities in this region of Mexico, and the long-term sustainability of these landscapes, depend on the resolution of this issue and thus it is of central importance when evaluating desertification.}, keywords = {desertification}, author = {E. Huber-Sannwald and J. F. Reynolds and Jeffrey E. Herrick and F. Maestre} } @inbook {50475, title = {Understanding global desertification: biophysical and socioeconomic dimensions of hydrology}, booktitle = {Dryland Ecohydrology}, year = {2006}, month = {January 2006}, pages = {315-332}, publisher = {Springer}, organization = {Springer}, address = {The Netherlands}, abstract = {This chapter reviews some of the key concerns and challenges associated with dryland desertification, emphasizing the role of hydrological processes. Hydrological processes are a function of complex interactions and linkages between specific patch types and landscape units; and thus, one of the keys to understanding both the causes and consequences of land degradation. Degradation involves a reduction in the ability of the land to support one or more functions. The interpretation of change as "loss" is dependent upon the context of the socioeconomic activities of human beings. The chapter ends with a discussion of future directions, including the development of the Dahlem Desertification Paradigm (DDP), a new approach to desertification designed to facilitate directed research effort and progress.}, keywords = {biophysical, desertification, hydrology, socioeconomic}, url = {/files/bibliography/06-050.pdf}, author = {F. Maestre and J. F. Reynolds and E. Huber-Sannwald and Jeffrey E. Herrick and Stafford-Smith, M.} } @inbook {50479, title = {Soil Development in the Jornada Basin}, booktitle = {Structure and Function of a Chihuahuan Desert Ecosystem. The Jronada Basin Long-Term Ecological Research Site}, year = {2006}, month = {July 1, 2006}, pages = {81-106}, publisher = {Oxford University Press}, organization = {Oxford University Press}, chapter = {4}, address = {New York, NY}, abstract = {Soils of the Jornada Basin are the substrate on which Jornada ecosystems reside and interact. Understanding soils and plant-soil feedback processes have been integral to understanding vegetation change and desertification. Formal studies of Jornada soils extend back to 1918. The most detailed study of Jornada soils is the USDA-SCS Desert Soil-Geomorphology Project, a 400-mi2 study area that includes the southernmost areas of the Jornada Experimental Range (JER) and Chihuahuan Desert Rangeland Research Center (CDRRC). This chapter highlights findings of soil and geomorphology studies, discusses factors and processes of soil development, and lists several ways soils of the Jornada Basin carry a memory of past climates.}, keywords = {change, desertification, development, soil, vegetation}, url = {/files/bibliography/06-055.pdf}, author = {Curtis H. Monger}, editor = {Kris Havstad and L. Huenneke and W. H. Schlesinger} } @article {50478, title = {The Soil-geomorphic template and biotic change in arid and semi-arid ecosystems}, journal = {Journal of Arid Environments}, volume = {65}, year = {2006}, month = {April 1, 2006}, pages = {207-218}, abstract = {

Desertification, characterized as biotic change toward a degraded state, is a common phenomenon in many arid and semiarid regions of the world. Such biotic change is often accompanied by and linked to geomorphic change. Important geomorphic factors that determine the vulnerability of a system to coupled biotic and abiotic change includes soil, topography, and soil parent material{\textemdash}which together form the soil-geomorphic template. Soil exerts control because it is the substrate that provides water, nutrients, anchorage for roots, and habitat for burrowing animals. Topography exerts control by its influence on microclimate via water redistribution, aspect, and elevation. Soil parent material exerts control by its contribution to the nutrient supply and formation of soil. Numerous linkages and feedback-loops occur between the soil-geomorphic template, micro-climate, vegetation, and animals. A perturbation in any of these factors can steer an ecosystem from one state to another. Some soil-geomorphic templates are more prone to change than others. For example, landscapes with sandy soils are more vulnerable to desertification than landscapes with fine-textured soils that receive run-in water and, therefore, require distinct management practices. Desertification involving simultaneous changes in biotic and geomorphic processes provides a good example of how biological and geological systems are coupled and co-evolve.

}, keywords = {biotic, change, desertification, geomorphic, soil, topography}, doi = {10.1016/j.jaridenv.2005.08.012}, url = {/files/bibliography/06-008.pdf}, author = {Curtis H. Monger and Brandon T Bestelmeyer} } @article {50480, title = {Multiscale controls on and consequences of aeolian processes in landscape change in arid and semi-arid environments}, journal = {Journal of Arid Environments}, volume = {65}, year = {2006}, month = {April 1, 2006}, pages = {253-275}, abstract = {Aeolian processes are tightly linked to soil and vegetation change in deserts at multiple spatial and temporal scales. Wind influences patterns of vegetation and soil within the landscape, while these patterns control wind erosion at patch to landscape scales. Aggregated at larger scales, patterns in soil and vegetation distributions influence global distributions of dust and its biogeochemical impacts. Understanding the controls on aeolian processes is, therefore, important not only in understanding the biogeochemistry and land cover patterns in dryland environments but also in understanding global land cover, climate, and biogeochemistry. These relationships are poorly understood, particularly for structurally complex plant communities such as shrub-invaded grasslands. The objective of this paper is to review the controls on aeolian processes and their consequences at plant-interspace, patch-landscape, and regional-global scales. Based on this review, we define the requirements for a cross-scale model of wind erosion in structurally complex arid and semi-arid ecosystems. http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WH9-4H1004J-1-1N\&_cdi=6845\&_user=1496926\&_orig=browse\&_coverDate=04\%2F30\%2F2006\&_sk=999349997\&view=c\&wchp=dGLbVtb-zSkWA\&md5=e74666463d89e6fd5315d4fde2958934\&ie=/sdarticle.pdf}, keywords = {aeolian processes, desertification, dust emission, landscape change, wind erosion}, url = {/files/bibliography/06-010.pdf}, author = {Gregory S. Okin and D. E. Gillette and Jeffrey E. Herrick} } @article {50483, title = {Disentangling complex landscapes: new insights into arid and semiarid system dynamics}, journal = {BioScience}, volume = {56}, number = {6}, year = {2006}, month = {June 2006}, pages = {491-501}, abstract = {

Although desertification is a global phenomenon and numerous studies have provided information on dynamics at specific sites, spatial and temporal variation in response to desertification have led to alternative, and often controversial, hypotheses about the key factors that determine these dynamics. We present a new research framework that includes five interacting elements to explain these dynamics: (1) historical legacies, environmental driving variables, (3) a soil-geomorphic template, (4) horizontal and vertical transport vectors, and (5) redistribution of resources within and among spatial units. We offer a six-step operational approach that is applicable to many landscapes, and illustrate its utility for understanding present-day landscape organization, forecasting future dynamics, and making effective management decisions.

}, keywords = {alternative states, cross-scale interactions, desertification, feedbacks and thresholds, nonlinear dynamics}, doi = {10.1641/0006-3568(2006)56[491:DCLNII]2.0.CO;2}, url = {/files/bibliography/06-021.pdf}, author = {Debra C. Peters and Brandon T Bestelmeyer and Jeffrey E. Herrick and E.L. Fredrickson and Curtis H. Monger and Kris Havstad} } @article {50523, title = {Multi-scale factors and long-term responses of Chihuahuan Desert grasses to drought}, journal = {Landscape Ecology}, volume = {21}, number = {8}, year = {2006}, note = {//USDA//LTER IV//entered 7/12/2006; updated 10/16/2006}, month = {2006}, pages = {1217-1231}, chapter = {1217}, abstract = {

Factors with variation at broad (e.g., climate) and fine scales (e.g., soil texture) that influence local processes at the plant scale (e.g., competition) have often been used to infer controls on spatial patterns and temporal trends in vegetation. However, these factors can be insufficient to explain spatial and temporal variation in grass cover for arid and semiarid grasslands during an extreme drought that promotes woody plant encroachment. Transport of materials among patches may also be important to this variation. We used long-term cover data (1915\–2001) combined with recently collected field data and spatial databases from a site in the northern Chihuahuan Desert to assess temporal trends in cover and the relative importance of factors at three scales (plant, patch, landscape unit) in explaining spatial variation in grass cover. We examined cover of five important grass species from two topographic positions before, during, and after the extreme drought of the 1950s. Our results show that dynamics before, during, and after the drought varied by species rather than by topographic position. Different factors were related to cover of each species in each time period. Factors at the landscape unit scale (rainfall, stocking rate) were related to grass cover in the pre- and post-drought periods whereas only the plant-scale factor of soil texture was significantly related to cover of two upland species during the drought. Patch-scale factors associated with the redistribution of water (microtopography) were important for different species in the pre- and post-drought period. Another patch-scale factor, distance from historic shrub populations, was important to the persistence of the dominant grass in uplands (Bouteloua eriopoda) through time. Our results suggest the importance of local processes during the drought, and transport processes before and after the drought with different relationships for different species. Disentangling the relative importance of factors at different spatial scales to spatial patterns and long-term trends in grass cover can provide new insights into the key processes driving these historic patterns, and can be used to improve forecasts of vegetation change in arid and semiarid areas.

}, keywords = {arid grasslands, desertification, drought, grazing, perennial grasses, transport processes}, doi = {10.1007/s10980-006-0025-8}, url = {/files/bibliography/06-034.pdf}, author = {Jin Yao and Debra C. Peters and Kris Havstad and Gibbens, Robert P. and Jeffrey E. Herrick} } @conference {50541, title = {Modeling aeolian processes in the context of desertification}, booktitle = {20th Annual Symposium of the U.S. Regional Chapter of the International Association for Landscape Ecology}, year = {2005}, note = {poster presentation}, month = {03/2005}, pages = {61}, address = {Syracuse, NY}, abstract = {

Conversions from grasslands to shrublands have occurred throughout arid and semiarid regions globally over the past several centuries. Although a number of factors have been implicated as drivers of this conversion (e.g., grazing by livestock, drought, climate change), the key drivers responsible for vegetation change in any particular location are controversial. This controversy is due in large part to the large spatial variation in shrub invasion success through time. At the Jornada Experimental Range in southern New Mexico, we are taking a multi-scale approach to understanding and forecasting landscape scale dynamics associated with these desertification processes. As part of our approach, we are developing a spatially interactive model that simulates interactions and feedbacks between the vegetation, soil properties, and aeolian transport to explain and forecast vegetation dynamics at multiple spatial scales.\  Dynamic vegetation patches vary in size and composition that affect fetch and hence erosion and deposition of soil particles by wind. Wind speed data is given using a Weibull distribution derived from empirical data. Preliminary results show that aeolian transport is a key driver of conversions from grasslands to shrublands that depends on spatial characteristics of soil texture and vegetation.

}, keywords = {aeolian, conversions, desertification, modeling, multi-scale, shrublands, simulation}, author = {J.D. Daues and Debra C. Peters and Daues, G.} } @conference {50580, title = {Soil Geomorphic Change During Desertification}, booktitle = {Agronomy Society of America, Crop Science Society of America, Soil Science Society of America Meetings}, year = {2005}, month = {November 6-10, 2}, pages = {200-5}, address = {Salt Lake City, UT}, abstract = {The objective of this paper is to illustrate the concept of the soil-geomorphic template and its relationship to biotic change. Desertification, as an example of biotic change toward a degraded state, is a common phenomenon in many arid and semiarid regions of the world. Such biotic change is typically accompanied by and linked to geomorphic change. Geomorphic factors that are involved in biotic change are soil, topography, and soil parent material, which together form the soil-geomorphic template. Soil is involved because it is the substrate that provides water, nutrients, anchorage for roots, and habitat for burrowing animals. Topography is involved by its influence on microclimate via elevation, lateral redistribution of water, and slope aspect. Soil parent material is involved by its contribution to the nutrient supply. Numerous linkages and feedback-loops occur between the soil-geomorphic template, microclimate, vegetation, and animals. A perturbation in any of these factors can steer an ecosystem from one state to another. Some soil-geomorphic templates are more prone to change than others. For example, landscapes with sandy soils are more vulnerable to desertification than landscapes with fine-textured soils that receive run-in water and, therefore, require distinct management practices. Desertification involving simultaneous changes in biotic and geomorphic states provides a good example of how biological and geological systems are coupled and co-evolve.}, keywords = {desertification, geomorphic, soil}, author = {Curtis H. Monger and Brandon T Bestelmeyer} } @article {50593, title = {Aspectos Socioeconomicos Y Biofisicos de la Desertificaction}, journal = {International Journal of Ecology and Evironmental Sciences}, year = {2005}, month = {September 30, 20}, abstract = {Land degradation and desertification are among the most important environmental issues being faced by drylands. Despite its importance and the enormous research effort devoted to it in the last decades, desertification is a topic surrounded by controversy and disagreement. This controversy is rooted in the traditional separation of the biophysical and socio-economic dimensions of desertification, which have been studied separately by scientists from both the natural and the social sciences. This separation has been fueled by the lack of a conceptual and synthethic framework suited to deal with both dimensions simultaneously. In this article we review the main topics surrounding desertification, introduce a new conceptual framework designed to study the biophysical and socio-economic dimensions of desertification simultaneously, review some of the measures being carried out to manage desertified lands and discuss some of the main challenges ahead in the research and management arenas.}, keywords = {degradation, desertification}, url = {/files/bibliography/05-019.pdf}, author = {J. F. Reynolds and F. Maestre and E. Huber-Sannwald and Jeffrey E. Herrick and P. R. Kemp} } @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 {50715, title = {The role of animals in desertification: Herbivory patterns in degraded grassland}, booktitle = {89th Annual Meeting, Ecological Society of America}, year = {2004}, month = {August 1, 2004}, pages = {Abstract p. 438}, address = {Portland, OR}, abstract = {We examined the contribution herbivores make to the resistance and resilience of desert grassland ecosystems following a desertification process. The study took place in the Jornada Experimental Range, New Mexico, where, historically, desert grassland has gone through the desertification process during the past century. We monitored browsing signs on snakeweed (Gutierrezia sarothrae), the dominant sub-shrub in the landscape, and on all perennial grass species. Snakeweed was monitored for browsing on a monthly basis over a period of a year, while grasses were evaluated for herbivory in a single assessment at the end of their growing season. Plots grazed by livestock for 3 subsequent years were compared with undisturbed ones. Domestic animals grazing ceased in 1998, hence all herbivory documented is related to wild rabbits and rodents. Results show clear spatial and temporal herbivory patterns on snakeweed. The animals browsed in patchy patterns and have shown significant tendency for repeated browsing on specific plants, which indicates a nonrandom feeding behavior. Relatively high browsing frequency and biomass intake were documented between November and March, which forms the dry season in the northern Chihuahuan Desert. A significant decrease in snakeweed browsing was detected with the appearance of annuals and ceased almost completelywith the availability of perennial grasses. Despite the temporal pattern detected, plant-water content failed to explain the herbivore spatial feeding preferences. Grasses had much lower initial abundance and biomass compared to snakeweed. This resulted in a significantly higher relative percentage of grass biomass consumed by herbivory. That effect strongly intensified in formerly grazed plots where initial grass cover was the lowest. By the end of their growing season almost no grass flowering tillers survived which caused insufficient seed reservoir. Our findings show that herbivores contribute to the resistance and resilience of degraded grasslands by reducing the reestablishment of grasses.}, keywords = {desert grassland ecosystems, desertification, herbivory patterns, role of animals}, author = {Roth, G.A. and Walter G. Whitford and Yosef Steinberger} } @conference {50731, title = {Landscape-scale analyses provide new insights into desertification}, booktitle = {19th Annual Symposium of the US Regional Association of the International Association for Landscape Ecology: Transdisciplinary Challenges in Landscape Ecology}, year = {2004}, month = {March 30-April 2}, address = {Las Vegas, NV}, abstract = {Desertification, or the invasion of woody plants into perennial grasslands with associated changes in ecosystem stability, is a pervasive problem that affects arid and semiarid systems worldwide. Although many studies have been conducted on woody plant invasion, we still lack a basic understanding of controls on the spatial and temporal variation in desertification dynamics at multiple scales. Our objective was to develop and test a new conceptual framework of woody plant invasion that explicitly includes a hierarchy of interacting scales. Our model includes landscape characteristics, such as connectivity, interacting with both fine scale processes (e.g., competition) and broad-scale drivers (e.g., climate) to generate cross-scale interactions. We provide support for our model from a combination of long-term studies, process-based experiments, and integrative simulation model analyses conducted in southern New Mexico. Results from >100 permanent quadrats established in the early 1900{\textquoteright}s show both high spatial and temporal variation in patterns in shrub invasion and grass persistence through time. Much of this variation was explained by landscape-scale features related to connectivity of shrubs (i.e., distance to the nearest shrubland when a quadrat was established). Experimental results show the importance of variation in herbivory on grass survival at grass-shrub ecotones with high spatial variation among locations. An integrated simulation model and multiscale experiments are being used to examine key processes and constraints operating across scales. Thus, our results support the cross-scale landscape model of desertification and provide a framework for understanding and predicting variation in woody plant invasion dynamics.}, keywords = {cross-scale, desertification, invasion, landscape-scale, woody plants}, url = {http://abstracts.co.allenpress.com/pweb/usiale2004}, author = {Jin Yao and Debra C. Peters and Kris Havstad and Brandon T Bestelmeyer} } @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 {50893, title = {Desertification alters patterns of aboveground net primary production in Chihuahuan ecosystems}, journal = {Global Change Biology}, volume = {8}, year = {2002}, note = {//NMSU,USDA//LTER IV//}, month = {2002}, pages = {247-264}, abstract = {

The Chihuahuan desert of New Mexico has changed in historical times from semiarid grassland to desert shrublands dominated by Larrea tridentata and Prosopis glandulosa. Similar displacement of perennial grasslands by shrubs typifies desertification in many regions. Such structural vegetation change could alter average values of net primary productivity, as well as spatial and temporal patterns of production. We investigated patterns of aboveground plant biomass and net primary production in five ecosystem types of the Jornada Basin Long-Term Ecological Research (LTER) site. Comparisons of shrub-dominated desertified systems and remnant grass-dominated systems allowed us to test the prediction that shrublands are more heterogeneous spatially, but less variable over time, than grasslands.We measured aboveground plant biomass and aboveground net primary productivity (ANPP) by species, three times per year for 10 years, in 15 sites of five ecosystem types (three each in Larrea shrubland, Bouteloua eriopoda grassland, Prosopis dune systems, Flourensia cernua alluvial flats, and grass-dominated dry lakes or playas). Spatial heterogeneity of biomass at the scale of our measurements was significantly greater in shrub-dominated systems than in grass-dominated vegetation. ANPP was homogeneous across space in grass-dominated systems, and in most growing seasons was significantly more patchy in shrub vegetation. Substantial interannual variability in ANPP complicates comparison of mean values cross ecosystem types, but grasslands tended to support higher ANPP values than did shrub-dominated systems. There were significant interactions between ecosystem type and season.Grasslands demonstrated higher interannual variation than did shrub systems. Desertification has apparently altered the seasonality of productivity in these systems; grasslands were dominated by summer growth, while sites dominated by Larrea or Prosopis tended to have higher spring ANPP. Production was frequently uncorrelated across sites of an ecosystem type, suggesting that factors other than season, regional climate, or dominant vegetation may be significant determinants of actual NPP.

}, keywords = {article, articles, climate change, community dynamics, climate, Chihuahuan Desert, climate, desertification, climate, grassland, desertification, journal, journals, Larrea tridentata, net primary production, plant community, change, plant community, creosotebush, plant community, diversity, plant community, mesquite, plant community, productivity, plant community, tarbush, plant community, vegetation sampling, plant, environmental change, plant, Flourensia, plant, Larrea tridentata, plant, primary production, plant, productivity, plant, Prosopis, plants, net primary production, playa, productivity, playa, vegetation patterns, prosopis glandulosa}, doi = {10.1046/j.1365-2486.2002.00473.x}, url = {files/bibliography/JRN00354.pdf}, author = {L. Huenneke and John P. Anderson and M.D. Remmenga and W. H. Schlesinger} } @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} } @inbook {50937, title = {Desertification}, booktitle = {Encyclopedia of Global Change}, year = {2002}, note = {//??//LTER III//ProCite field[6]: In}, month = {2002}, pages = {253-256}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {Oxford}, keywords = {book, books, chapter, chapters, desertification, report, reports}, author = {W. H. Schlesinger}, editor = {A.S. Goudie and Cuff, D. J. (eds.)} } @article {51027, title = {Degradation of sandy arid shrubland environments: observations, process modelling, and management implications}, journal = {Journal of Arid Environments}, volume = {47}, year = {2001}, note = {//USDA//LTER IV// In file and Updated 12/15/2005}, month = {2001}, pages = {123-144}, abstract = {

Field remote sensing, and modelling observations from a degraded Mojave Desert shrubland were used to develop a model of the progressive degradation of areas adjacent to sites of direct anthropogenic disturbance. Aeolian removal and transport and dust, sand, and litter are the primary mechanisms of degradation, killing plants by burial and abrasion, interrupting natural processes of nutrient accumulation, and allowing the loss of soil resources by abiotic transport. It is concluded that any arid shrubland with wind-erodible soils is susceptible to degradation, and where possible development of these lands should be avoided.

}, keywords = {agriculture, article, articles, desertification, journal, journals, landscape, ecosystem dynamics, management, shrublands, model, process, Mojave Desert, paleolakes, shrubland, degradation, shrublands, wind erosion}, doi = {10.1006/jare.2000.0711}, url = {files/bibliography/JRN00324.pdf}, author = {Gregory S. Okin and Murray Bruce and W. H. Schlesinger} } @inbook {51035, title = {Desertification}, booktitle = {Encyclopedia of Biodiversity, Volume 2}, year = {2001}, note = {//NONE//NONE//ProCite field[6]: InProCite field[8]: Editor-in-ChiefProCite field[36]: In}, month = {2001}, pages = {61-78}, publisher = {Academic Press}, organization = {Academic Press}, address = {San Diego, CA}, abstract = {The phenomenon of desertification involves the loss of biological or economic productivity and biodiversity in arid and semiarid croplands, pastures, rangelands, and subhumid woodlands due mainly to nonsustainable human activities, such as overcultivation, fuel gathering, overgrazing by domestic animals, deforestation, and poor irrigation practices, and is often triggered or exacerbated by climate variability, mainly drought.}, keywords = {book, books, chapter, chapters, desertification, model, desertification, report, reports}, author = {J. F. Reynolds}, editor = {Simon Asher (ed. Levin} } @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} } @conference {51085, title = {Jornada Basin LTER: Linkages in semiarid landscapes}, booktitle = {85th Annual Meeting, Ecological Society of America}, year = {2000}, month = {August 8-10, 200}, pages = {Abstract p. 396}, address = {Snowbird, UT}, abstract = {Chihuahuan Desert landscapes exemplify the ecological conditions, vulnerability, and management issues found in semiarid regions around the globe. The goal of the JRN-LTER program is to identify the key factors controlling ecosystem dynamics in semiarid landscapes with the objective of understanding the causes and consequences of desertification. Previous work has focused primarily at the scale of a single plant-interspace and the redistribution of resources at that scale. Our central hypothesis for LTER IV is that landscape position and linkages among landscape units exert important influences on ecosystem dynamics and biotic patterns. We propose to build upon our understanding of resource redistribution at the plant-interspace scale in several ways. We will synthesize existing long-term data with new studies on linkages among landscape units. We will conduct simulation model analyses to test the relative importance of within- versus between-unit processes. We will initiate studies of landscape fluxes of water, nutrients, and organisms to evaluate key processes affecting ecosystem dynamics at this scale. We will also employ remote sensing to assess fluxes and processes at larger spatial scales. Cross-site studies will be used to test the generality of our hypotheses for application to management and remediation of semiarid ecosystems and desertified landscapes.}, keywords = {desertification, ecosystem dynamics, LTER, remote sensing, semiarid, simulation model}, author = {L. Huenneke and Kris Havstad and Jeffrey E. Herrick and David C. Lightfoot and Curtis H. Monger and Debra C. Peters and A. Rango} } @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} } @inbook {51111, title = {Drylands and global change: Rainfall variability and sustainable rangeland production}, booktitle = {Proceedings of the 12th Toyota Conference: Challenge of Plant and Agricultural Sciences to the Crisis of the Biosphere on the Earth in the 21st Century}, year = {2000}, note = {//NMSU,USDA//LTER III//ProCite field[6]: In}, month = {2000}, pages = {73-86}, publisher = {R. G. Landes Company}, organization = {R. G. Landes Company}, address = {Austin, Texas}, abstract = {This chapter reviews the extent of global change in drylands and some of its ecological and societal consequences. It also discusses rainfall variability as one component of potential climate change and how it affects primary production in rangelands. This is illustrated with a case study of a rangeland in southern New Mexico using a physiologically-based ecosystem model. It suggests that basic ecological knowledge should be an essential component of assessment frameworks.}, keywords = {book, books, chapter, chapters, climate variability, global change, desertification, global change, rainfall variability, global change, rangeland production, model, PALS, plant production, rainfall variability, rainfall, global change, rainfall, rangeland production, rangeland production, global change, report, reports}, author = {J. F. Reynolds and Roberto J. Fern{\'a}ndez and P. R. Kemp}, editor = {Watanabe, K. N. and Komanine, A. (eds.)} } @inbook {51153, title = {Desert rangelands, degradation and nutrients}, booktitle = {Rangeland Desertification}, year = {1999}, month = {1999}, pages = {77-87}, publisher = {Kluwer Academic Press}, organization = {Kluwer Academic Press}, address = {Dordrecht, The Netherlands}, abstract = {

It is well recognized that rangeland environments, especially degraded environments, are relatively infertile. Though arid lands are moisture limited, it is often stated that they are nutrient regulated. A discussion of rangeland soil nutrients relative to landscape degradation should include: (1) dynamics of nutrient distributions; (2) soil properties affecting nutrient fluxes; (3) indicators of soil quality; and 4) nutrient based strategies for remediation. Nutrient distribution is strongly influenced by vegetation structure, and spatial nutrient patterns are closely linked to aspects of primary productivity and species composition. Effects of vegetation on nutrient spatial patterns can persist for decades, even if vegetation is altered by natural or anthropogenic disturbances. Though abiotic processes strongly shape physical features of arid landscapes, biotic activities directly affect soil nutrients. Unfortunately, assessment and monitoring technologies based on soil properties which quantify integrity of nutrient related processes have not been fully developed. Approaches for remediating degraded conditions need to exploit nutrient spatial and temporal heterogeneities. Remediation should be targeted to the most fertile sites, even if these are only relatively small parts of the overall landscape. Understanding nutrient dynamics is a key to triggering autogenic remediation of degraded rangelands.

}, keywords = {desert grassland, desertification, nitrogen, nutrient dynamics, phosphorus}, doi = {10.1007/978-94-015-9602-2_7}, url = {/files/bibliography/661.pdf}, author = {Kris Havstad and Jeffrey E. Herrick and W. H. Schlesinger}, editor = {Arnalds, O. and Steven R. Archer} } @article {51164, title = {Soil microarthropods as indicators of exposure to enviromental stress in Chihuahuan Desert rangelands}, journal = {Biololgy and Fertility of Soils}, volume = {28}, year = {1999}, month = {1999}, pages = {121-128}, abstract = {

We studied soil microarthropod communities along livestock grazing disturbance gradients, inside and outside grazing exclosures, and on areas subjected to restoration efforts (herbicide and bulldozing) in order to test the suitability of mites as indicators of rangeland soil quality. We found that mite numbers generally increased with decreased grazing disturbance. Soil microarthropods appeared to respond to a complex of factors including soil compaction, depth to an impervious soil layer, below-ground vegetative biomass, and residual effects of herbicide. All of our study plots, except those that had been herbicide treated, were dominated by microbivorous mites of the family Nanorchestidae. The numerical responses of mites, especially nonorchestids, appeared to provide a sensitive indicator of ecosystem health in a Chihuahuan Desert grassland.

}, keywords = {desert grassland, desertification, grazing, Herbicides, indicators.}, doi = {10.1007/s003740050472}, url = {/files/bibliography/669.pdf}, author = {F. R. Kay and Sobhy, H. M. and Walter G. Whitford} } @article {51173, title = {Spatial and temporal variability in relative abundance and foraging behavior of subterranean termites in desertified and relatively intact Chihuahuan Desert ecosystems}, journal = {Applied Soil Ecology}, volume = {12}, year = {1999}, month = {1999}, pages = {149-157}, abstract = {

The annual feeding activity on paper baits of subterranean termites in desertified (degraded-shrub dominated ecosystems) and relatively undegraded black-grama (Bouteloua eriopoda) grasslands was measured over six years on 12 sites. There were no significant differences in mass losses from termite baits among the desertified and undesertified sites. Mass of paper consumed by termites on two sites dominated by creosotebush, Larea tridentata, was higher than on the other 10 sites. These sites were characterized by shallow, coarse soils and shrubs that did not retain a below-canopy litter layer. The spatial locations of the highest termite bait removal remained relatively constant over the duration of the study. Interannual variations in mass losses from termite baits were highly correlated with winter{\textendash}spring rainfall (r2 between 0.60 and 0.95) except at one site on shallow soils. The relationship between annual rainfall and termite activity was less significant (r2 between 0.48 and 0.83). Frequency of attack as measured by percent of bait rolls {\textquotedblleft}hit{\textquotedblright} were not different among sites indicating no differences in densities of subterranean termites. Degradation of Chihuahuan desert grasslands and associated vegetation change has had minimal effect on the activity of subterranean termites. Subterranean termites continue to affect soil properties and processes in both degraded (desertified) and undesertified ecosystems.

}, keywords = {desert grassland, desertification, dunes, Shrub-lands, Subterranean termites}, doi = {10.1016/S0929-1393(98)00164-4}, url = {/files/bibliography/673.pdf}, author = {M. S. Nash and John P. Anderson and Walter G. Whitford} } @article {51185, title = {Impact of drought on desert shrubs: Effects of seasonality and degree of resource island development}, journal = {Ecological Monographs}, volume = {69}, number = {1}, year = {1999}, month = {February 1, 1999}, pages = {69-106}, abstract = {

Large areas of semiarid grasslands in the southwestern United States have been virtually replaced by shrubs during the past century. Understanding the causes and consequences of such vegetation dynamics requires that we elucidate the interplay between external forces of change (e.g., climate, human impacts) and the internal forces within these ecosystems that foster resilience and/or stability. Several conceptual models of and ecosystems address this interplay by including the potential role of autogenic shrub effects on ecosystem processes that lead to the formation of "resource islands" and tend to promote shrub persistence. Specifically, during the process of shrub establishment and maturation, the cycling of nutrients is progressively confined to the zones of litter accumulation beneath shrubs, while bare intershrub spaces become increasingly nutrient poor. As shrub resource islands develop, there is increased interception and stemfiow by shrub canopies, confining infiltration of nutrient-enriched rainfall directly beneath the shrubs; the barren intershrub spaces generate overland flow, soil erosion by wind and water, and nutrient losses. These islands are preferred sites for the regeneration of shrubs and herbaceous plants and are correlated with spatial variation in soil microbial populations and soil microfauna that promote nutrient cycling. If further changes in the transition between grassland and shrubland are to be correctly predicted, or if we wish to intervene and redirect transitions, we must develop a greater mechanistic understanding of the structural and functional relationships between shrubs and the resource islands associated with them.

}, keywords = {desertification, drought response, Jornada LTER, Larrea tridentata, prosopis glandulosa, resource island formation, shrub physiology, soil nitrogen, soil water}, doi = {10.2307/2657195 }, url = {/files/bibliography/680.pdf}, author = {J. F. Reynolds and R. A. Virginia and P. R. Kemp and A.G. de Soyza and Tremmel, D. C.} } @article {51186, title = {Nutrient losses in runoff from grassland and shrubland habitats in Southern New Mexico: I. rainfall simulation experiments}, journal = {Biogeochemistry}, volume = {45}, year = {1999}, note = {//NMSU,USDA//LTER III//}, month = {1999}, pages = {21-34}, abstract = {

Rainfall simulation experiments were performed in areas of semiarid grassland (Bouteloua eriopoda) and arid shrubland (Larrea tridentata) in the Chihuahuan desert of New Mexico. The objective was to compare the runoff of nitrogen (N) and phosphorus (P) from these habitats to assess whether losses of soil nutrients are associated with the invasion of grasslands by shrubs. Runoff losses from grass- and shrub-dominated plots were similar, and much less than from bare plots located in the shrubland. Weighted average concentrations of total dissolved N compounds in runoff were greatest in the grassland (1.72 mg/l) and lowest in bare plots in the shrubland (0.55 mg/l). More than half of the N transported in runoff was carried in dissolved organic compounds. In grassland and shrub plots, the total N loss was carried in dissolved organic compounds. In grassland and shrub plots, the total N loss was highly correlated to the total volume of discharge. We estimate that the total annual loss of N in runoff is 0.25 kg/ha/yr in grasslands and 0.43 kg/ha/yr in shrublands -- consistent with the depletion of soil N during desertification of these habitats. Losses of P from both habitats were very small.

}, keywords = {article, articles, desertification, grassland, hydrology, grassland, hydrology, nutrient export, hydrology, rainfall simulation, hydrology, shrubland, hydrology, surface runoff, journal, journals, nitrogen, nutrient budgets, phosphorus, runoff}, doi = {10.1023/A:1006020831706}, url = {files/bibliography/JRN00282.pdf}, author = {W. H. Schlesinger and Athol D. Abrahams and A.J. Parsons and John Wainwright} } @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 {51248, title = {Plant-soil interactions in deserts}, journal = {Biogeochemistry}, volume = {42}, year = {1998}, note = {//USDA//LTER-III//}, month = {1998}, pages = {169-187}, abstract = {

Geostatistical analyses show that the distribution of soil N, P and K is strongly associated with the presence of shrubs in desert habitats. Shrubs concentrate the biogeochemical cycle of these elements in "islands of fertility" that are localized benath their canopies, while adjacent barren, intershrub spaces are comparatively devoid of biotic activity. Both physical and biological processes are involved in the formation of shrub islands. Losses of semiarid grassland in favor of invading shrubs initiate these changes in the distribution of soil nutrients, which may promote the further invasion and persistence of shrubs and cause potential feedbacks between desertification and the Earth{\textquoteright}s climate system.

}, keywords = {article, articles, biogeochemistry, calcite, biogeochemistry, calcium carbonate, biogeochemistry,desertification, biogeochemistry,nitrogen, desertification, erosion, geostatistics, journal, journals, nitogen, phosphorus, Prosopis, soil nutrients, soil heterogeneity, soil, aridisols, soil, nutrients}, doi = {10.1023/A:1005939924434 }, url = {files/bibliography/JRN00260.pdf}, author = {W. H. Schlesinger and A. M. Pilmanis} } @article {51313, title = {Desertification and animal biodiversity in the desert grasslands of North America}, journal = {Journal of Arid Environments}, volume = {37}, year = {1997}, month = {1997}, pages = {709-720}, abstract = {

Studies of breeding birds and small mammals were conducted at a series of sites that form a gradient of severity of desertification. Desert grassland sites represented the least changed landscape units and mesquite coppice dunes represented the most severe degradation, an irreversibly degraded landscape unit. The hypothesis that desertification reduces species diversity was not supported by the data. Species richness and diversities (Shannon-Weaver H') of breeding birds were higher in the desertified areas than in the grassland with one exception. Data from a site dominated by the exotic African grass, Eragrostis lehmanniana, in south-eastern Arizona showed that breeding bird diversity was lower at that site than at a site in the same region that was dominated by native grasses. Species richness, diversity (H'), and abundance of small mammals were also higher in desertified areas than in desert grassland. Most grassland species of birds and mammals persist in the desertified habitats and species that are characteristic of shrublands colonize desertified desert grasslands. This accounts for the increases in species richness. However some species such as the banner-tailed kangaroo rat, Dipodomys spectabilis, are eliminated when grassland degrades to mesquite coppice dune or eroded creosotebush communities. These data suggest that other measures of faunal biodiversity such as keystone species may be better measures of the impact of desertification on animal biodiversity.

}, keywords = {biodiversity, breeding birds, desert grasslands, desertification, exotic species, rodents}, doi = {10.1006/jare.1997.0313}, url = {/files/bibliography/600.pdf}, author = {Walter G. Whitford} } @proceedings {51350, title = {Shrublands and grasslands of the Jornada Long-Term Ecological Research Site: desertification and plant community structure in the northern Chihuahuan Desert}, volume = {Gen. Tech. Rep. INT-GTR-338}, year = {1996}, note = {//NMSU,USDA//LTER-III//ProCite field[6]: InProCite field[8]: Compilers}, month = {May 23-25, 1995}, pages = {48-50}, publisher = {U.S. Department of Agriculture, Forest Service, Intermountain Research Station}, address = {Las Cruces, NM}, abstract = {Semidesert grasslands of southern New Mexico have been replaced in this century with shrublands (chiefly creosote bush and mesquite). The Jornada Long-Term Ecological Research Program has been monitoring aboveground plant productivity, plant species composition, and other aspects of ecosystem function in 15 sites. Plant diversity differs significantly among vegetation types, with grasslands being the most diverse. Aboveground net primary productivity does not differ significantly among vegetation types. Productivity is correlated with plant species richness in some seasons; however, diversity has not been correlated with smaller fluctuation of production between years in the first few years of study. These results have implications for sustainable management of diversity and of productivity.}, keywords = {abstract, abstracts, conference, conference proceedings, conferences, desertification, plant community, diversity, plant community, productivity, plant community, structure, plant, diversity, plant, productivity, proceeding, proceedings}, author = {L. Huenneke}, editor = {J.R. Barrow and McArthur, E.D. and R. E. Sosebee and R. J. Tausch} } @article {51381, title = {Relationships between landforms, geomorphic processes, and plant communities on a watershed in the northern Chihuahuan Desert}, journal = {Landscape Ecology}, volume = {11}, number = {6}, year = {1996}, note = {//NMSU//LTER III//}, month = {1996}, pages = {351-362}, abstract = {

The close correlation of plant communities to landforms and geomorphic surfaces resulted from differences in the redistribution of water and organic matter between landforms in the northern Chihuahuan Desert. Biotic processes are limited by water and nitrogen, and the interactions between landforms, geomorphic processes, soils, and plant communities control the redistribution of these limiting resources within internally drained catchments. Geomorphic processes are regulated by the geologic structure and gross topographic relief of internally drained catchments over geological time scales. Land forming processes can be viewed as static at time scales of 10{\textquoteright}s to 100{\textquoteright}s of years, with individual landforms regulating geomorphic processes, namely erosion and deposition resulting from the horizontal redistribution of water within the catchment. The vegetation composition is a critical feedback, reinforcing the erosional or depositional geomorphic processes that dominate each landform. The Jornada Long-Term Ecological Research site may be one of the simplest cases in which to decipher the relationship between landforms, geomorphic processes and plant communities. However, these geomorphic processes are common to all internally drained catchments throughout the Basin and Range Province, and result in the development of characteristic landforms and associated vegetation communities. Although the patterns may be modified by differences in parent material, watershed size, and land use history -- erosional, depositional, and transportational landforms can still be identified. The sharpness of ecotones between plant communities on individual landforms is related to the degree to which landforms are linked through the flow of water and sediment. Sharp ecotones occurred at the transition from depositional to erosional landforms where little material was transferred and steep environmental gradients are maintained. Gradual ecotones occurred at the transition from erosional to depositional landforms where large quantities of material were transferred leading to the development of a gradual environmental gradient. The relationships between geomorphic processes and vegetation communities that we describe have important implications for understanding the desertification of grasslands throughout semi-arid regions of North America. disturbances such as grazing and climate change alter the composition of plant communities, thereby affecting the feedbacks to geomorphic processes, eventually changing drainage patterns and the spatial patterns of plant communities supported within the landscape.

}, keywords = {article, articles, deposition, desertification, ecotones, erosion, grassland, grazing, journal, journals, limiting resources, runoff, shrubland, water availability}, doi = { 10.1007/BF02447522 }, url = {files/bibliography/JRN00217.pdf}, author = {Steven M. Wondzell and Gary L. Cunningham and Bachelet Dominique} } @conference {51465, title = {Persistence of desertified ecosystems: explanations and implications}, booktitle = {International Symposium and Workshop on Desertification in Developed Countries: Why Can{\textquoteright}t We Control It?}, year = {1994}, month = {October 24-29, 1}, pages = {18-19}, address = {Tucson, AZ}, abstract = {

Desertification in much of the southwestern U.S. and northern Mexico has resulted in the replacement of perennial grasslands with desert scrublands. Scrublands dominated by C3 shrubs exhibit long-term persistence, resist control efforts, and are resilient in areas where control and revegetation with grasses have been attempted. Experiments using 5 consecutive years of summer drought using \"rain-out\" shelters and 5 consecutive years of approximately doubling the summer rainfall resulted in no significant changes in annual net above-ground primary production of creasotebush, barren tridentata, in either of the treatments. There were significant changes in species composition and above-grind net primary production of spring annual plants and some reduction of perennial grasses and fortis in droughted plots. There were small changes in decomposition rates and nitrogen mineralization potential but no quantitative differences in the Studies of shrub water budgets demonstrated that between 6 percent and 25 percent of the intercepted rainfall was translocated to deep soil storage by stemflow and root channelization. Nutrient minerals in stemflow water on creosotebush were 5 to 10 times more concentrated in stemflow than in thrnttghfsli and bulk precipitation. These data demonstrate that once shrubs are established, islands of resource enrichment of water and nutrients develop under the shrubs. The result is self-reinforcing systems that are resistant to disturbance. The characteristics of the shrub-dominated ecosystems documented in the experiments demonstrate that they are likely to persist with climate change. The data from these studies suggest that management of desertified landscapes in North America should focus on maintaining the residual grasslands and on the economic uses of the shrub-dominated ecosystems.

}, keywords = {desert scrublands, desertification, desertified landscapes, maintaining grasslands, management}, author = {Walter G. Whitford and G. Martinez-Turanzas and E. Martinez-Meza} } @book {51534, title = {Desertification}, series = {Encyclopedia of Earth Science}, year = {1992}, note = {//??//LTER II//Listed in LTER3 proposal as citing LTER2 support// Updated 12/17/2005ProCite field[6]: In}, month = {1992}, publisher = {Academic Press}, organization = {Academic Press}, address = {San Diego}, keywords = {book, books, chapter, chapters, desertification, report, reports}, author = {W. M. Jarrell} } @article {51548, title = {Soil biota and soil properties associated with surface rooting zone of mesquite (Prosopis glandulosa) in historical and recently desertified Chihuahuan Desert habitats}, journal = {Biology and Fertility of Soils}, volume = {14}, year = {1992}, note = {//NMSU, USDA//LTER II//Listed in LTER3 proposal as citing LTER2 support//}, month = {1992}, pages = {90-98}, abstract = {

The woody legume, mesquite (Prosopis glandulosa) has expanded from its historical habitats (playas and arroyos) to recently occupied grassland and dune habitats during the desertification of perennial grasslands in the Chihuahuan Desert. We studied historical and recently occupied sites, having hypothesized that the trophic structure and population density of soil microarthropods and nematodes associated with the surface root system of mesquite would differ in sites representing historical and recent habitats, and that the N mineralization potential would be lower in the recent habitats. Our results showed that net N mineralization potential did not differ significantly among the sites, even though soil nutrient concentrations and texture varied widely. Concentrations of organic C, N, and P were lowest in the recent dune habitat and highest at the playa. Very low concentrations of P in the dune and grassland soils implicated P as a limiting factor in these systems. The bacterial-feeding and omnivore-predator functional groups made up the largest fraction of the nematode community at most of the sites. The high density of plant-feeding nematodes at the playa indicated that herbivory is potentially most important at this site. Total microarthropod densities did not vary significantly among habitats, with Collembola densities highest in the mesquite dunes. Grazers were the dominant microarthropod functional group. While both C and N pool sizes were higher in the historical habitats, a higher substrate lability in the recent habitats appeared to support biota populations and N mineralization rates equivalent to those in the playa and arroyo. Differences in soil properties and biota among historical and recent mesquite habitats may be important for understanding the changes that have occurred in Chihuahuan Desert ecosystems during desertification.

}, keywords = {article, articles, collembola, community,Prosopis, desertification, journal, journals, microarthropod,Prosopis soils, nematode, nitrogen mineralization, nutrients, nitrogen mineralization, Prosopis, Prosopis, soil biota, Prosopis,rooting zone, Prosopis,soil properties, soil properties}, doi = {10.1007/BF00336256}, url = {files/bibliography/92-Biol\&FertofSoils-Whitford.pdf}, author = {R. A. Virginia and W. M. Jarrell and Walter G. Whitford and D. W. Freckman} } @proceedings {51785, title = {A baseline of soil erosion and vegetation monitoring in desert grasslands: Chihuahua, Texas and New Mexico}, volume = {General Technical Report RM-150}, year = {1987}, note = { //NMSU//NONE//ProCite field[6]: In}, month = {October 12-16, 1}, pages = {214-220}, publisher = {USDA Forest Service, Rocky Mountain Forest and Range Experiment Station}, address = {Tucson, Arizona}, abstract = { A long-term monitoring for vegetation and soil changes in desert grasslands of the northern Chihuahuan Desert was started in 1981 as part of the USDA/SEA Antidesertification program. Five study areas were located on the Jornada Experimental Range, Otero Mesa, and Peloncillo Mountains in New Mexico, Big Bend National Park in Texas, and Rancho La Campana in Chihuahua, Mexico. Vegetation was charted in quadrats along 30m permanent transects in these study areas. A high-precision auto-level was used to establish baseline data on the current soil-surface levels along the transects. In the future, recharting vegetation and remeasuring soil-surface level should provide data on rates of change. This data could be used to validate models designed to predict rates of soil erosion and vegetation change.}, keywords = {abstract, abstracts, conference, conference proceedings, conferences, desertification, long term monitoring, soil erosion, model, validation data, proceeding, proceedings, soil erosion, transect, soil erosion, transect, vegetation, vegetation transect}, author = {J. Ludwig and Moir, William H.}, editor = {Earl F. Aldon and Gonzales-Vicente, C. E. and Moir, W. H. (eds.)} } @article {51803, title = {A hierarchical classification of landforms: some implications for understanding local and regional vegetation dynamics}, year = {1987}, note = {//NMSU//LTER I//Listed in LTER2 proposal as citing LTER1 support//ProCite field[6]: In}, month = {1987}, pages = {15-23}, institution = {USDA Forest Service, Rocky Mountain Forest and Range Experiment Station}, address = {Fort Collins, Colorado}, abstract = {

Analyses of soils and vegetation on the Jornada/Long-Term Ecological Research site have shown strong relationships between vegetative communities and landforms. Observations indicate that similar vegetative patterns exist throughout the Mexican Highland division of the Basin and Range Province. A generalized landscape-level model is presented which attempts to explain the desertification trends producing the shrub-grassland vegetational mosaic found today in southern New Mexico.

}, keywords = {book, books, chapter, chapters, community, landforms, community, vegetative, desertification, geomorphology, transect, geomorphology, vegetation dynamics, landforms, classification, model, desertification, report, reports, transect, geomorphology, transect, landforms, transect, plant communities, transect, vegetation dynamics, vegetation dynamics, vegetation, classification, vegetative communities}, isbn = {General Technical Report RM-150}, url = {files/bibliography/JRN00048.pdf}, author = {Steven M. Wondzell and Gary L. Cunningham and Dominique Bachelet}, editor = {Earl F. Aldon and Carlos E. Gonzale Vicente and Moir, William H. (eds.)} }