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

2023 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 dry fall, winter, and early spring resulted in the stakeholder group deciding to substantially reduce stocking rates due to very low available forage and unfavorable seasonal climate outlooks. This decision was facilitated using a newly developed remote sensing tool that provides probabilities of forage biomass values at the pasture scale. New research efforts assessed enteric methane emissions of individual yearling cattle from herds originating in different climates. Emissions from the same set of yearlings were measured using GreenFeed systems in late winter and again during summer grazing on the shortgrass steppe. Other new research tested the use of virtual fence to modify cattle movement within a pasture, excluding cattle from sensitive riparian zones, and quantifying patterns of forage use. 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 combination of additional early spring water and increased interannual precipitation variability began to positively affect shrub cover and density after five years of treatment. 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 is testing the degree to which early spring grazing, during the predicted grazing windows, can shift plant community composition towards desirable native species. We selected a site that was heavily invaded by cheatgrass, added water tanks and fencing to construct six replicated pastures, and have now implemented the first two years of early spring grazing treatments. Preliminary plant response data suggests that targeted grazing may effectively control cheatgrass in both wet and dry years. 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 the Thunder Basin site. 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 this site. 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. Zoomable maps now allow users to decide for themselves whether the amount precipitation assumed by Grass-Cast is similar enough to precipitation received on their specific pasture or allotment to trust resulting production estimates. Grass-Cast projections were used to determine the number of yearlings needed for the flexible stocking rate study, designed to adaptively match animal demand with forage availability. Wind Erosion Prediction System (WEPS) Webstart was implemented by the Natural Resources Conservation Service (NRCS) in July for determining wind erosion estimates for conservation practices. A new web-based interface for the WEPS is nearing completion and will provide capacity to run both WEPS and the Water Erosion Prediction Project (WEPP) model together. The APEX (Agricultural Policy/Environmental eXtender Model) model is being enhanced to address spatial and temporal variability at CPER by dividing each pasture into sub-pastures with uniform soil and plant properties and to simulate soil carbon and nitrogen dynamics with the improved CENTURY module under different grazing management practices. A visualization tool is being developed using R statistical software to facilitate APEX calibration and data analysis.

Accomplishments
1. Water use efficiency indicators across agricultural systems. Agricultural production is challenged by water scarcity and competition among users for available water. Increasing water use efficiency (production output per unit of water input) is therefore a primary objective of agricultural management, breeding, and engineering. Although water use efficiency can be determined for spatial scales from the individual leaf to the entire farm/ranch, and for time scales of a few seconds to years, the measurement and interpretation of water use efficiency varies across these scales, making comparisons difficult. ARS researchers in Fort Collins, Colorado, led a Long-Term Agroecosystem Research (LTAR) network effort to review common water use efficiency indicators across diverse agroecosystems and production environments across the Nation. Focusing on a single water use efficiency indicator across complex agricultural systems is misleading as it may have unintended consequences at different spatial or time scales. Rather, water use efficiency indicators should be carefully selected to address specific scientific questions, effects of management practices, or impacts of climate change.

2. Rotational grazing reduces diet quality and weight gain. Adaptive, rotational grazing management practices are hypothesized to enhance certain ecosystem services, such as forage and livestock productivity and soil carbon sequestration, yet very few experiments have evaluated how or why they affect livestock production, which has the greatest consequences for ranch economics. ARS researchers from Fort Collins, Colorado, and Cheyenne, Wyoming, used GPS tracking devices to quantify foraging behavior of cattle managed via adaptive, multi-paddock rotational grazing, and compared this with foraging behaviors of cattle grazing under a traditional, season-long management regime. They showed that rotational grazing management altered individual steer foraging behaviors in ways that led to reduced diet quality (less selective foraging), and in turn reduced cattle weight gain by 14% over a 5-year period. Findings document the mechanism by which rotational grazing management can reduce cattle productivity and identify stock density (herd size relative to pasture size) as a key factor managers should consider when developing grazing management regimes to achieve multiple outcomes on extensive rangelands. During May 2023, these findings were highlighted in more than 25 agricultural media outlets (e.g., Beef Magazine, On Pasture, Western Ag Reporter) in the U.S. and Canada with potential outreach to >4.7 million consumers.

3. Soil disturbance magnifies climate change effects on rangeland. Although human disturbances affect much of the world’s land area, their interactions with climate change are poorly understood. ARS researchers in Fort Collins, Colorado, and the University of Wyoming, tested how effects of elevated carbon dioxide and warming differed in intact mixedgrass rangeland and disturbed rangeland with invasive plants. They found that intact rangeland was relatively resistant to global change effects, but that this resistance was lost through disturbance. The combination of soil disturbance and plant invasion (1) magnified elevated carbon dioxide effects on productivity 10-fold, (2) reversed elevated carbon dioxide effects on plant diversity, and (3) combined with warming to slow recovery of soil carbon. Results suggest that limiting soil disturbance and controlling plant invasion through common rangeland management practices may be even more important under future climatic conditions. Land managers and policy makers can use these results to help prioritize conservation efforts and invasive species management in rangeland ecosystems.

U.S. DEPARTMENT OF AGRICULTURE

Rangeland Resources & Systems Research: Fort Collins, CO