Project : USDA ARS

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Research Project: Adaptive Grazing Management and Decision Support to Enhance Ecosystem Services in the Western Great Plains

Location: Rangeland Resources & Systems Research

2021 Annual Report

Objectives
Objective 1-Determine the potential for adaptive grazing management to enhance beef production, vegetation heterogeneity, grassland bird conservation, carbon/energy/water balance, and soil health in western Great Plains rangelands. Subobjective 1.1–Compare responses of livestock, wildlife, plants, and soils to adaptive grazing management and traditional grazing management. Subobjective 1.2–Determine the contribution of flexible stocking strategies, adjusted annually based on forecasted weather and forage availability, to the sustainable intensification of livestock production. Subobjective 1.3–Determine the contribution of genetic variability (source population) in livestock, and its interaction with environmental variability and management strategies, to variability in livestock performance. Objective 2-Evaluate the impacts of droughts and deluges on shrub-grass interactions and carbon/energy/water fluxes and balances; learn how livestock management affects these responses. Subobjective 2.1–Quantify the effects of precipitation variability, extreme events (seasonal to multi-year droughts and individual deluges), topoedaphic variation, and livestock management on forage, livestock production, and carbon/energy/water fluxes. Subobjective 2.2–Evaluate the effects of increased interannual and intraannual precipitation variability and soil texture on grass-shrub competition, plant production, and forage quality. Objective 3-Identify temporal windows for spring grazing of cheatgrass to increase invasion resistance and forage production. Subobjective 3.1–Quantify temporal patterns of cattle consumption of cheatgrass and native, cool-season perennial grasses. Predict ideal grazing windows from associated measurements of climate, plant phenology, and forage quality. Subobjective 3.2–Test the utility of predicted grazing windows for controlling cheatgrass and increasing forage production. Objective 4-Evaluate where, when, and to what extent prairie dogs suppress livestock production in western Great Plains rangelands by altering forage resources and livestock foraging behavior. Subobjective 4.1–Quantify relationships between cattle weight gains and prairie dog abundance at pasture scales, at multiple sites, and across multiple years. Subobjective 4.2–Evaluate whether spatiotemporal patterns of livestock foraging can explain the mechanisms by which prairie dog abundance and distribution affect livestock weight gains. Objective 5-Provide land managers with information and decision tools needed to maintain profitability and environmental sustainability, and reduce risk to livestock operations in a changing climate. Subobjective 5.1–Simulate effects of adaptive grazing management on forage and livestock production in a spatially and temporally complex rangeland ecosystem; use simulations to explore alternative scenarios for stakeholder decision making. Subobjective 5.2-Evaluate the Wind Erosion Prediction System (WEPS) model at site and regional scales of rangeland agroecosystems. Subobjective 5.3-Develop interactive learning experiences and social networks to enhance stakeholder capacity for risk management and adaptation in a changing climate.

Approach
Semiarid rangelands of the western Great Plains simultaneously support livestock production and other ecosystem services such as wildlife habitat and soil carbon storage. To enhance decision-making by managers in these complex socio-ecological systems, we must first understand processes that regulate the provision of ecosystem services. The interactive effects of climate, soils, and management on forage production, plant invasion, livestock weight gain, and wildlife habitat are poorly understood. Moreover, key tools available to rangeland managers—adjusting stocking rates to match animal demand to forage availability, and moving livestock to better utilize spatially and temporally variable forage resources—are often underutilized. Through the coordinated and interdisciplinary work of eight scientists, we propose to: 1) conduct collaborative adaptive grazing management experiments, with direct involvement of diverse stakeholders, to balance multiple ecosystem services; 2) use intensive measurements of carbon fluxes and soil water to discover how precipitation interacts with topographic and edaphic variation to influence forage productivity and cattle weight gain; 3) use site-level models and cross-site comparisons to enhance predictions of key rangeland processes, including livestock weight gain and wind erosion; and 4) enhance stakeholder capacity for risk management and adaptation in a changing climate. To help achieve these goals we will leverage extensive historical data from the western Great Plains, participate in regional/national research efforts with other ARS units (e.g., Long Term Agroecosystem Research Network, USDA Climate Hubs, Grand Challenges, National Wind Erosion Network), and actively engage university partners, livestock producers, and other stakeholders.

Progress Report
The first objective focuses on the Collaborative Adaptive Rangeland Management experiment, located in shortgrass steppe at the Central Plains Experimental Range (CPER). A summer drought presented novel challenges for stakeholders starting in early June with hot temperatures, low precipitation, and rapidly deteriorating forage conditions. The Stakeholder Group implemented adaptive decision-making with drought-induced vegetation residue thresholds, splitting the one large herd into two to reduce stocking density impacts, and re-grazing of some pastures during the grazing season. Reduced forage biomass and quality due to the hotter, drier conditions sharply reduced livestock weight gains. New research efforts field-quantified cattle bite numbers, rate, and size with direct observations and jaw movement detection devices which provide a mechanistic understanding of these grazing behaviors to animal weight gains on semiarid rangeland. New cattle GPS collars, designed within the unit, integrated location and accelerometer devices to determine grazing behavior patterns with improved temporal resolution (seconds rather than 5-minute intervals). The second objective is focused on how changes in precipitation influence the hydrology and productivity of semiarid rangelands. We incorporated eddy covariance data into an analysis by the Long-Term Agroecosystem Research (LTAR) Phenology working group. At the CPER, we tested interactive effects of droughts and deluges on forage production and carbon cycling using both a precipitation manipulation experiment and a long-term (36-year) observational study of plant productivity data from a topographic sequence. In the Thunder Basin region of northeastern Wyoming (where sagebrush grassland, shortgrass steppe and northern mixed-grass prairie converge), we are using a precipitation manipulation experiment to test effects of: 1) greater interannual precipitation variability, and 2) more precipitation in the winter/early spring on plant productivity, drought stress and phenology. Preliminary results indicate that higher precipitation variability may negatively impact livestock forage in this system. Prior year addition of water followed by drought the next year led to high abundance of invasive annual bromes, but perennial grass production was resistant to increased precipitation variability. The third objective is focused on early spring grazing for control of cheatgrass in mixedgrass rangeland (High Plains Grasslands Research Station). We have completed the first study, which enabled us to predict when cattle select for and against cheatgrass both within and among years. We used those predictions to create grazing windows - phenological periods when cattle are likely to be most effective in controlling cheatgrass. The second study will test the degree to which early-spring grazing can shift plant community composition towards desirable native species. We have selected a site, collected preliminary data on plant species composition and productivity, and will start treatments in spring 2022. The fourth objective is focused on interactions between prairie dogs and cattle in the western Great Plains. We monitored cattle foraging behavior via GPS collars at both the CPER and in Thunder Basin. We also collected data on prairie dog densities, vegetation composition, cattle diet quality, forage quality, and weight gains throughout the summer and fall (from branding to weaning) from these same sites. Results will help us to understand the impacts of prairie dogs and plague (which periodically decimates prairie dog colonies), as well as the drivers and consequences of cattle foraging behavior decisions. We have also continued to measure the separate and combined effects of prairie dogs, livestock, and native grazing animals on forage quality, quantity, and composition via a long-term nested exclosure project in Thunder Basin. For each project, we provided data summaries to ranchers participating in these projects. The fifth objective addresses the provision of information and decision tools to land managers. The USDA Northern Plains Climate Hub continued to work with livestock producers and other rangeland managers to prepare for increasing weather variability and a changing climate. Grass-Cast, a grassland production forecasting tool that currently serves the Great Plains and the Southwest states of New Mexico and Arizona (https://grasscast.unl.edu) is a product of the USDA Northern Plains Climate Hub. Outreach efforts reached at least 500 stakeholders during 12 virtual events, including a “Facebook Live” event hosted by ARS’s Office of Communications for producers, land managers, agencies, and organizations. A new version of the Wind Erosion Prediction System (WEPS), a process-based simulation model for conservation planning, management, and assessment of environmental impacts of wind erosion, was finalized for the Natural Resources Conservation Service (NRCS). This version includes a new plant growth model and alignment of operation and crop/residue records with the Water Erosion Prediction Project (WEPP) model. Rangeland and dryland cropping sites are being monitored for the National Wind Erosion Research Network (NWERN) that will parameterize the Aeolian Erosion (AERO) model. The APEX (Agricultural Policy/Environmental eXtender Model) model was enhanced and used to simulate grazing management practices (traditional vs. adaptive grazing management) at two LTAR sites: the semiarid rangeland, Central Plains Experimental Range, and the mesic grassland, Texas Gulf.

Accomplishments
1. New stocking rate guide reveals 72% increase in grazing capacity for semiarid rangelands. A stocking rate guide developed by ARS has been used for four decades on semiarid rangelands in the United States and around the world to relate grazing animal performance (weight gain) and beef production per unit area to remaining forage at the end of the grazing season. ARS scientists from Cheyenne, Wyoming, and Fort Collins, Colorado, in collaboration with scientists from the University of Wyoming, analyzed contemporary data (2000-2018) from the same long-term study (1939-current) initially used for the 1960s stocking rate guide. They determined that the sustainable stocking rate for semiarid rangelands in the western Great Plains increased by 72% over the past 50 years, likely due to combined effects of recovery from the 1930s Dust Bowl, elevated atmospheric carbon dioxide concentration, and livestock genetics. The revised guide, available on the web as a Colorado State University extension fact sheet, is being used by more than 60 ranchers and on approximately 200,000 acres of the United States Forest Service Pawnee National Grassland for adaptive stocking adjustments to increase profitability, production efficiency, and resilience of the semiarid shortgrass steppe rangeland.

2. Quantifying plant traits to restore drought resistant rangelands. Managing for drought is one of the biggest challenges in rangelands. Plant drought-tolerance traits provide a powerful tool for predicting plant community responses to drought but are not well understood. Scientists from ARS in Fort Collins, Colorado, and Cheyenne, Wyoming and Colorado State University discovered that easy-to-measure drought tolerance traits can predict which species grow most consistently across wet and dry years. These drought tolerant species stay green later in the year and persist in grazed ecosystems, which means they provide reliable sources of forage in semiarid rangeland. The ability to restore drought tolerant plant communities facilitates long-term conservation efforts and improves resilience of rangeland to a changing climate.

3. Sensitivity of forage production in a semiarid rangeland to precipitation and topography. Sensitivity of forage production in a semiarid rangeland to precipitation and topography. Understanding how precipitation amount and pattern as well as topographic variability impact forage production are critical to sustainable livestock management. Scientists from ARS in Fort Collins, Colorado, and Cheyenne, Wyoming, Yale University, and Colorado State University, used long-term (1983-2018) productivity and precipitation data to examine patterns and drivers of variability in forage production. Forage production varies up to 4-fold across topographic gradients, and is sensitive to precipitation amount as well as within year precipitation patterns. These results are helping ranchers and land managers using adaptive management to match animal demand with available forage under highly variable climatic conditions. The long-term productivity data are being used for validation and calibration of the Agricultural Policy/Environmental eXtender rangeland model, and in a Long-Term Agroecosystem Research Network analysis of water-use efficiency.

U.S. DEPARTMENT OF AGRICULTURE

Rangeland Resources & Systems Research: Fort Collins, CO