• Complex landscapes in the American Southwest: are desertified systems “novel”? (D Peters, S Archer, O Sala, E Vivoni, KM Havstad, C Monger, J Yao, N Burruss) - Novel ecosystems are often defined as no-analog communities consisting of new combinations of species that assembled under new abiotic conditions. In the Anthropocene, novel systems differ from the historical state as a result of human influences where self organizational processes prevail to make these ecosystems unlikely to revert to their historical structure/function. Degraded shrub-dominated ecosystems that developed following livestock overgrazing and drought in arid and semiarid grasslands are a potential example of novel ecosystems. Although the self organization and stability of desertified ecosystems have been well-studied, these ecosystems have not been tested as novel ecosystems.
• The ecology of catastrophic events: understanding abrupt spatial transitions in susceptibility of grasslands and croplands to multi‐year drought (ND Burrus, D Peters, J Yao, et al) - Much of the central grasslands region (CGR) of North America experienced a multi‐year extreme drought in the 1930s that combined with land management practices to result in broad‐scale plant mortality, massive dust storms, and losses of soil and nutrients.
• Forecasting regional grassland responses to directional changes in climate using multi-year dry or wet periods (D Peters, J Yao, N Burrus, et al) - Ecologists are being challenged to predict ecosystem responses under changing climatic conditions. Although air temperatures are increasing, the magnitude and direction of change in precipitation (increase or decrease) are uncertain for many sites. Given that water availability is the primary driver of ecosystem processes in temperate grasslands and shrublands, these uncertainties in precipitation mean that ecologists must account for both possibilities. Long term research sites (LTER, LTAR) provide natural experiments for ecological responses that occurred historically during multiyear dry or wet periods that can be used to make predictions under future climate scenarios.
• Simulated distribution of an invasive grass, Lehmann lovegrass, in the Chihuahuan Desert under future climate scenarios  (J Yao, D Peters) - 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 suggest, qualitatively, that climate (precipitation and temperature) determines spatial variation in the current distribution of the species in the two Southwest deserts. We assumed that controls on seedling establishment represent the drivers on the distribution of this short-lived bunchgrass. Our goal was to quantify the climatic and edaphic controls on Lehmann lovegrass seedling establishment in order to predict where in the Chihuahuan Desert it may become invasive under alternative climate scenarios.
• Critcal Climate Period for Net Primary Production in Chihuahuan Desert Ecosystems (J Yao, D Peters) - In desert ecosystems where water is the main limiting factor, it is expected that net primary production (NPP) is largely determined by precipitation. However, precipitation alone often explains only a small portion of the variation in NPP. We examined the importance of four climate-related variables to patterns in NPP: precipitation (PPT), vapor pressure deficit (VPD), soil water content (SWC), and plant available water (PAW). Our goal was to identify the timing and duration of each variable (i.e., critical climate period) that correlates well to NPP, and to determine the variables that best explain variation in NPP for grasslands and shrublands in the Chihuahuan Desert. The study site, Jornada Basin USDA-LTER site (32.5N, 106.45W), is located in the northern Chihuahuan Desert, southern New Mexico, USA. Climate is arid to semiarid with a 96-year average of 25 cm of annual precipitation, of which 53% occurs during the monsoon season (Jul – Sep). Average monthly temperatures range from 6 ^oC in January to 26 ^oC in June.
• Climatic Modoki and Biotic Contingency: Drivers of Ecosystem Response to Extreme Events (D Peters, J Yao, D Browning, M Duniway, J Anderson, K Havstad, F Pillsbury) - Global environmental change is resulting in regional increases in the frequency of extreme climatic events, including multi-year wet or dry periods. Most of the focus on ecological impacts of multi-year events has been on drought periods, yet multi-year wet periods are also expected. In the Chihuahuan Desert, two naturally-occurring sequences of wet years (1984-1988, 2004-2008) occurred that were preceded by a sequence of dry years. Recent analyses showed grass production in the second wet period, particularly in shrublands, increased nonlinearly as the number of sequential wet years increased (Peters et al., 2012). These responses were attributed to recruitment by the dominant grass, either black grama in grasslands or mesa dropseed in shrublands (Peters et al., in review). Our objectives were: (1) to determine if a similar grass response occurred in the first wet period (1984-88), and (2) to identify the climate and soil properties governing grass responses in the two wet periods.
• Ecological Catastrophes: Threshold Responses to Climate, Soil, and Land use Drivers of the Dust Bowl (S Peters Scroggs, D Peters, K Havstad, C Monger, D Blumenthal, J Derner, S Kronberg, B Northup, G Okin, M Sanderson, J Steiner - The Dust Bowl was one of the world’s largest environmental disasters, yet it is among the least well-studied for landscape- to regional-scale ecological impacts. In the 1930s, much of the central grasslands region (CGR) of North America experienced a multi-year drought. Combined with spatially-extensive cultivation and overgrazing, the drought led to broad-scale plant mortality, massive dust storms, and decreases in continental-scale air quality. These impacts were collectively called the “Dust Bowl”. Although regional accounts exist, most studies focus on effects of abandoned agricultural land in a relatively small area centered on the panhandle of Oklahoma. However, these impacts were also documented on intact grasslands throughout the Great Plains. A recent synthesis of these data show spatial variation across the region: high grass mortality occurred throughout the western and central Great Plains whereas only reductions in grass cover primarily occurred in the east. A 145-km transition zone was found in the tallgrass prairie between high plant mortality near Crete, NE compared with cover loss without mortality near Glenwood, IA. Understanding the drivers of this variation in grass response is important to predicting dynamics of this region under future long-term drought and occurrence of dust storms.
• Critical Precipitation Period: Controls on Primary Production at Jornada Basin LTER (J Yao, D Peters) - In hot deserts, precipitation is the principal driver for net primary production; however, precipitation at coarse temporal resolutions (e.g., annual or seasonal) explains a small portion of variance in production. Precipitation at fine temporal resolutions (e.g., daily) can not explain variation in seasonal or annual production, either. Our goal was to identify the intermediate temporal resolutions (between daily and yearly) of precipitation that are critical to seasonal and annual production in the Chihuahuan Desert.
• Jornada Basin LTER: Landscape Linkages and State Changes Across Spatial and Temporal Scales (D Peters, K Havstad, C Monger, B Bestelmeyer, S Archer, S Bestelmeyer, M Duniway, J Herrick, G Okin, A Rango, O Sala, N Sayre, R Schoolev, R Skaggs, H Throop, C Tweedie, E Vivoni) - To understand and quantify the mechanisms that generate alternative natural and human-dominated states in dryland ecosystems and to predict future states and their consequences for the provisioning of ecosystem services, we work across a range of interacting spatial and tempoaral scales with a focus on important vegetation-soil geomorphic units found at the Jornada, across the American Southwest, and in aridlands globally. We have active research projects and collaborations on six continents.
• Long-term Studies Provide Insights to Diverse Terrestrial and Aquatic Ecosystem Dynamics (J Yao, D Peters) - Environmental drivers are changing at local to global scales with corresponding effects on ecological dynamics. Large amounts of data have been collected to document these changes. However, much of the data remain inaccessible to a broad audience. Therefore, solutions to these environmental problems have been elusive. The EcoTrends Project is one of the first attempts to standardize, simplify, integrate, and visualize data from diverse terrestrial, aquatic, and marine ecosystems to promote understanding and synthesis by a broad audience.