@conference {JRN54427, title = {Projected future distribution of an invasive grass, Lehmann lovegrass, in the Chihuahuan Desert}, booktitle = {2015 LTER All Scientists Meeting}, year = {2015}, month = {08/2015}, address = {Estes Park, CO}, abstract = {

Lehmann lovegrass (Eragrostis lehmanniana), an invasive grass dominating many grassland sites in the Sonoran Desert, has had a limited distribution in the Chihuahuan Desert.\  Climate (precipitation and temperature) is suggested to be the main driver for the difference in the current spatial distributions of the species in the two deserts. Our goal was to predict the distribution of Lehmann lovegrass throughout the Chihuahuan Desert under current climate conditions and future climate scenarios. We used the SOILWAT model to simulate Lehman lovegrass seedling establishment at \> 60 locations in the US portion of the Chihuahuan Desert. We then extrapolated the results to the entire region by using the 1981-2010 mean precipitation and temperature data from PRISM and the soil data from the SSURGO database. Future climate conditions were adjusted as follows: daily temperature was increased by 2.5 oC, and daily precipitation was increased or decreased by 5 and 10\%. Our results showed that the simulated distribution of Lehmann lovegrass in the Chihuahuan Desert under current climatic conditions is mainly in the southern part of the region, similar to the observed distribution. The spatial distribution under future climate scenarios varies due to the combined effects of precipitation and temperature. The species distribution contracts when precipitation decreases 5 or 10\% or daily temperature increases 2.5 oC. The species distribution expands when temperature stays the same and precipitation increases 5 and 10\%. Our study shows that the distribution of Lehmann lovegrass in the Chihuahuan Desert will depend on the amount and direction of changes in future temperature and precipitation. This uncertainty in the projected distribution adds one more challenge to land management of this invasive grass under climate change. Paper No. 120.

}, author = {Jin Yao and Debra C. Peters} } @conference {JRN54435, title = {Simulated distribution of an invasive grass, Lehmann lovegrass, in the Chihuahuan Desert under future climate scenarios}, booktitle = {100th Annual Meeting of the Ecological Society of America}, year = {2015}, month = {08/2015}, address = {Baltimore, MD}, abstract = {

ackground/Question/Methods Lehmann lovegrass (Eragrostis lehmanniana), a perennial grass introduced to the Southwest US in the 1930s from South Africa, has had a limited distribution in the Chihuahuan Desert while it has dominated many grassland sites in the Sonoran Desert.\  Previous observational studies and our site-based model simulations suggest that climate (precipitation and temperature) is the main driver for the difference in the current species{\textquoteright} distributions in the two Southwest deserts.\  Our goal was to predict the distribution of Lehmann lovegrass throughout the Chihuahuan Desert under current climate conditions and future climate scenarios.\  We used the SOILWAT simulation model to simulate Lehman lovegrass seedling establishment, with SSURGO data as input for soil related variables.\  The 1971-2000 mean precipitation and temperature from PRISM were used for the current climate conditions, and these data were adjusted based on the projected changes in National Climate Assessment for Southwest US to simulate future climate scenarios.

Results/Conclusions
Under current climatic conditions, the simulated distribution of Lehmann lovegrass in the Chihuahuan Desert is mainly in the southern portion of the desert, similar to observed populations. Under future climate scenarios, the spatial distribution of the species varies due to the combined effects of precipitation and temperature. The species distribution decreases when precipitation decreases or temperature increases a large amount. The species distribution expands when precipitation increases and temperature increases in low to moderate amounts. Our study shows that the distribution of Lehmann lovegrass in the Chihuahuan Desert will depend on the amount and direction of changes in future temperature and precipitation. This uncertainty in the projected distribution adds one more challenge to land management of this invasive grass under climate change.\  Abstract No. PS 18-177.

}, author = {Jin Yao and Debra C. Peters} } @inbook {JRN52668, title = {Cross-site studies "by design:" Experiments and observations that provide new insights}, booktitle = {Long-Term Trends in Ecological Systems: A Basis for Understanding Responses to Global Change}, year = {2013}, pages = {72-80}, publisher = {National Technical Information Services}, organization = {National Technical Information Services}, chapter = {10}, address = {Springfield, Virginia}, abstract = {

The cross-site comparisons presented in the previous chapters are all conducted after the individual studies are completed.\  The differences in experimental design in individual studies in a posteriori cross-site studies limit the scope of questions that can be addressed, and the powerfulness and confidence in the conclusions.\  This chapter describes cross-site studies that are {\textquotedblleft}by design{\textquotedblright} where the questions, experimental layout, methods, and measurements included multiple sites from the beginning. These a priori cross-site studies provide powerful tools to understand the phenomenon of global change and to predict its impacts on ecosystems and society. Two types of a priori cross-site studies are described: (1) experimental manipulations of drivers or system properties, and (2) observations or monitoring of natural or managed ecosystems located along environmental gradients. Within each type, examples of both on-going or completed experiments and new or developing experiments are presented.\  For each example, insights that would not have been obtained with other approaches are also presented. The limitations and difficulties of this type of studies are listed.

}, keywords = {atmospheric chemistry, climate change, cross-site comparisons, disturbance, ecological response, ecology, ecosystem, EcoTrends, experimental forests, global change, human demography, human population growth, Long Term Ecological Research (LTER), long-term datasets, precipitation, rangeland, rangeland research stations, surface water chemistry}, url = {/files/bibliography/13-029-10.pdf}, author = {Jin Yao and O. E. Sala and Debra C. Peters} } @proceedings {JRN54536, title = {Seasonal distribution of net primary production by functional groups in Chihuahuan Desert, and the role of seasonal precipitation}, volume = {PS 50-117.}, year = {2012}, month = {08/2012}, publisher = {Ecological Society of America Proceeding}, address = {Portland, Oregon}, abstract = {In hot deserts, precipitation is the principal driver for net primary production.~ This study tested two hypotheses regarding aboveground net primary production (ANPP) and the effects of precipitation on ANPP in the Chihuahuan Desert, with emphasis on differences among seasons and among functional groups of species. First, we hypothesized that the majority of annual ANPP occurs in the monsoon season.~ Second, we hypothesized that ANPP is positively correlated to precipitation. The study site, Jornada Basin USDA-LTER site, is located in the northern Chihuahuan Desert where Jul-Sep is the monsoon season during which 53\% of annual rainfall occurs.~ The ANPP and precipitation data were collected at 15 locations in 5 ecosystem types: 2 grassland types and 3 shrubland types (N=3 for each type) during 1990-2010.~ Three seasons were defined: winter (Oct {\textendash} Feb), spring (Mar {\textendash} May), and fall (Jun- Sep). ~ANPP was separated into three plant functional groups: C3 shrubs, C4 perennial grasses, and other plants (C3 and C4 annual forbs and grasses, and perennial forbs). Our results supported the first hypothesis for grasslands, but not for shrublands. On average, 67\% of annual ANPP in grasslands occurred in fall (range: 62-73\%); however, only 49\% of annual ANPP in shrublands occurred in fall (range: 41-58\%).~ Our second hypothesis was supported for some, but not all, functional groups and seasons. For example, in grasslands in general, fall perennial grass production was not related to fall precipitation. In shrublands winter and spring shrub production were high (winter: 5-21\% of annual ANPP, spring: 14-42\%, fall: 20-33\%), but they were not related to precipitation.~ In short, there were significant differences between desert grasslands and desert shrublands in terms of seasonal distribution of ANPP and response of ANPP to seasonal precipitation. ~This provides important information for understanding and projecting the impact of global climate change (e.g., change in seasonality, intensity, and frequency of precipitation) on structure and function of desert ecosystems.}, author = {Jin Yao and Debra C. Peters} } @proceedings {JRN54532, title = {Seasonal distribution of net primary production in Chihuahuan Desert shrublands and grasslands in response to precipitation from 1990-2010}, volume = {p. 42.}, year = {2012}, month = {05/2012}, publisher = {Wildland Shrub Symposium Proceedings}, address = {Las Cruces, NM}, abstract = {In arid and semiarid regions around the world, extensive areas of grasslands have been replaced by shrublands. A better understanding of the ecology of these shrublands compared to historical grasslands would help land managers make decisions for the sustainable provision of ecosystem goods and services. We compared aboveground net primary production (ANPP) and its response to precipitation between shrublands and grasslands in the Chihuahuan Desert, with an emphasis on differences among seasons and among functional groups of species. The study site, Jornada Basin USDA-LTER site, is located in the northern Chihuahuan Desert. The ANPP and precipitation data were collected at 15 locations in 5 ecosystem types: 3 shrubland types and 2 grassland types (N=3 for each type) during 1990-2010.~ Three seasons were defined: winter (Oct {\textendash} Feb), spring (Mar {\textendash} May), and fall (Jun- Sep). ~ANPP was separated into three plant functional groups: shrubs, perennial grasses, and others. The results showed significant differences between shrublands and grasslands in the seasonal pattern of ANPP, and in the relationship between precipitation at different time periods with seasonal ANPP. Compared to grasslands where ANPP was highest in the fall, shrubland ANPP occurred more evenly among all three seasons. For most locations, seasonal precipitation did not explain the most variation in the current season{\textquoteright}s ANPP. The precipitation period explaining the most variation in seasonal ANPP varied among ecosystem types and among locations within each type. These results suggest that other factors, such as soil water content, may be driving seasonal variation in ANPP, and that land management practices may need to be tailored to specific ecosystem types.}, author = {Jin Yao and Debra C. Peters} } @conference {50006, title = {Spatial heterogeneity in aboveground net primary production and species richness at multiple scales in the Chihuahuan Desert}, booktitle = {US-International Association for Landscape Ecology}, year = {2011}, month = {04/2011}, address = {Portland, OR}, abstract = {We analyzed patterns in spatial heterogeneity and the processes driving these patterns in two ecosystem properties, aboveground net primary production (ANPP) and species richness, at multiple scales in the Chihuahuan Desert.\  We used long-term data (1990-2009) to examine the importance of a suite of drivers and ecosystem properties to patterns in ANPP and species richness at two spatial scales: patch and landscape unit.\  Three patches were sampled annually within each of five landscape units: upland and playa grasslands, and mesquite, creosotebush, and tarbush shrublands. Spatial heterogeneity at the patch scale was measured as the coefficient of variation across quadrats (n = 48 or 49).\  Spatial heterogeneity at the landscape unit scale was measured as the coefficient of variation across patches.\  At the patch scale, heterogeneity was affected by growth form of the dominant plant species and by precipitation. Grasslands were more homogeneous than shrublands under drought conditions, but shrublands were more homogeneous in wet years. At the landscape unit scale, heterogeneity was mainly affected by variation in distance between patches and variation in precipitation. Because of high spatial heterogeneity across these diverse landscapes, we concluded that estimates of ANPP and species richness from fine scales can not be directly extrapolated to broader scales in the Chihuahuan Desert without accounting for both local and spatial drivers of processes.}, author = {Jin Yao and Debra C. Peters} } @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 {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} } @conference {50732, title = {Spatial and temporal variation in desertification due to stressors at multiple scales}, booktitle = {LAND Open Science}, year = {2004}, month = {December 2, 2004}, pages = {32}, address = {Morelia, Mexico}, abstract = {Desertification, in particular, shrub invasion into former grasslands, is a worldwide and well-known phenomenon in arid and semiarid areas; however, detailed quantification of spatial and temporal variation in desertification is rare. A number of interacting factors have been implicated for desertification, including livestock grazing, drought, herbivory by small animals, reduction in fire frequency, and global climate change; but, the exact role of these factors remains unclear. Using the long-term datasets collected at the Jornada Experimental Range, New Mexico, USA, we examined spatial and temporal variation in shrub invasion and grass persistence and identified the factors resulting in the variations. The dependent variables, basal area and annual growth of perennial grasses, were measured in 105 1 x 1 m permanent chart quadrats set up between 1915-32 and monitored annually until 1979, and periodically since that time. The explanatory variables included factors at both the local and landscape scales. The local factors considered were soil texture, depth to the top of caliche layer, precipitation, and micro-topography; the landscape factors were elevation, pasture stocking rate, and distance to historic shrublands. Our results showed that not all grasslands disappeared after the severe drought of 1950s: upland grass species (black grama, mesa dropseed, and threeawns) survived in a few quadrats and playa grass species (tobosa and burrograss) recovered to near pre-drought level in many quadrats. Spatial and temporal variations in grass persistence were results of interactions between climatic and landscape factors: both local and landscape factors affected grass persistence, but factors related to grass persistence varied with species and time period during 1915-2001. Our results increase our understanding of desertification in the face of global change and provide important information for the prediction of land cover change in arid and semiarid areas in the future.}, author = {Jin Yao and Debra C. Peters and Gibbens, Robert P. and Kris Havstad and Jeffrey E. Herrick} } @conference {50955, title = {Response of perennial grasses to precipitation in the northern Chihuahuan Desert: implications for grassland restoration}, booktitle = {87th Annual Meeting, Ecological Society of America}, year = {2002}, month = {August 4, 2002}, pages = {302}, address = {Tucson, AZ}, abstract = {Grasslands in the Chihuahuan Desert of the southwestern US have been invaded by less palatable shrubs over the past 50-100 years. Sustainable management and remediation of rangelands require detailed understanding of how various factors drive the conversion of grasslands to shrublands or allow grasslands to persist through time. We compared the impacts of precipitation on perennial grass cover by species during the course of shrub invasion with responses of grasses in areas where they have persisted. At the Jornada Experimental Range, NM, 106 1-m2 permanent quadrats were set up during 1915-1932 across a range of vegetation and soil texture types. Quadrats have been monitored periodically to quantify changes in cover through time. We separated the quadrats into two groups for the analysis: (1) quadrats that maintained dominance by perennial grasses through time, and (2) quadrats that were originally located in grasslands but were dominated by shrubs in 1995. We compared long-term data from 21 rain gauges with the vegetation data to identify the periods of rainfall to which abundance and growth of dominant species were the most sensitive for each species. Basal areas of black grama, mesa dropseed, and tobosa were correlated with long-term annual precipitation; the highest coefficients occurred with cumulative rainfall in the previous 6 to 8 years. Annual growth rates of these species were correlated with short-term rainfall occurring within the previous 15 months. Black grama response to precipitation was homogeneous among quadrats in persistent grasslands but heterogeneous among quadrats where shrubs currently dominate. Our results have important implications for remediation of desert grasslands since knowledge of grass responses to precipitation can be used to identify the windows of opportunity to initiate remediation projects.}, author = {Jin Yao and Debra C. Peters and Gibbens, Robert P. and Kris Havstad} } @conference {50956, title = {Spatial variation in shrub invasion and loss of perennial grasses in the Chihuahuan Desert: A multiscale approach}, booktitle = {17th Annual Symposium, US International Association for Landscape Ecology}, year = {2002}, month = {April 23-26, 200}, pages = {30}, address = {Lincoln, NE}, abstract = {Chihuahuan Deserts are characterized by large-scale invasion of perennial grasslands by shrubs over the past century. A number of interacting factors have been implicated in this invasion, including grazing by cattle, drought, herbivory by small animals, and reduction in fire frequency. Spatial variation in shrub invasion has been observed across these landscapes that cannot be explained using plot-scale studies. We investigated the relationship between spatial and temporal variation in these factors and the replacement of perennial grasses by shrubs using permanent 1 m2 quadrats sampled since 193. Quadrats (n=105) were located across the range of soil and plant communities found at the 78,266-ha Jornada Experimental Range LTER site in southern New Mexico, USA. We synthesized additional long-term data collected at multiple spatial scales to identify the factors that influence grass cover in the quadrats. Persistence of the dominant species, black grama, was positively related to processes at the quadrat (sand content, perennial grass production) and landscape scales (distance to nearest shrub-dominated community, variation in spring and winter rainfall). Grass persistence was negatively related to inter-annual variation in grass production. Our results can be used to identify the conditions most resistant to shrub invasion and most likely candidates for remediation.}, author = {Jin Yao and Debra C. Peters and Kris Havstad and Gibbens, Robert P. and Jeffrey E. Herrick} }