Location:2011 Annual Report
1a. Objectives (from AD-416)
Evaluate how management practices and disturbance processes interact to influence A) transitions/thresholds in ecological phases and states, B) plant community heterogeneity and nesting habitat for grassland birds, C) mechanisms and risk of weed invasion, and D) temporal dynamics of key ecological indicators of rangeland health. Subobjective A. Determine the influences of season and intensity of grazing, season and frequency of prescribed burning, and shifts in stocking rate on plant species composition, plant diversity, biomass production, animal gains and nesting habitat of a bird species of concern. Subobjective B. Evaluate the influences of fire X grazing interactions (i.e., patch burning) and prairie dog disturbances on within-pasture cattle grazing distribution, consequences for plant community heterogeneity and nesting habitat for a bird species of concern. Subobjective C. Determine how disturbance interacts with enemy release (the loss of specialized herbivores and diseases in the exotic range of a plant species) to influence weed invasion and the success of biological control. Subobjective D. Assess the temporal dynamics of key ecological indicators of rangeland health (plant cover and bare ground) for entire pastures in sagebrush and shortgrass steppe.
1b. Approach (from AD-416)
The planned research is designed to integrate contemporary goals of both livestock production and conservation in semiarid rangelands. Research will be conducted in shortgrass steppe, northern mixed-grass prairie and sagebrush steppe. Two experiments are replicated across three ARS locations (Miles City, MT; Nunn, CO; Woodward, OK) to determine ecological consequences of fire seasonality, return interval and grazing interactions along a north-south gradient in the western Great Plains. Rangeland monitoring efforts at two ARS locations with contrasting vegetation (grass-dominated shortgrass steppe, Nunn, CO; shrub-dominated sagebrush steppe, DuBois, ID) will use newly-developed techniques involving very large-scale aerial photography to assess plant cover and bare ground, and incorporate this information into a recently developed index to assess landscape function. Understanding the mechanisms that control disturbance effects on plant communities and animal responses will contribute to the development of innovative management strategies that optimize livestock production and conservation goals. In addition, because state-and-transition models function as a means for organizing current understanding of the processes resulting in stability and change in ecological systems, findings from these experiments will be incorporated into revised state-and-transition models of plant community dynamics that more accurately accommodate multiple successional pathways and stable states.
3. Progress Report
Progress was made on the main objective and four subobjectives, which address National Program 215 Objectives A.1, A.2, A.3, B., and C.1. Under Objective A.1 (Develop management and monitoring strategies and decision-support tools that conserve natural resources while maintaining economic objectives), we made substantial progress in developing management strategies that incorporate vegetation heterogeneity and maintain livestock production to assist land managers in managing for a blending of production and conservation objectives. We also assessed the financial costs of associated infrastructure (e.g., cross-fence) often added by land managers to facilitate prescribed grazing. Across the Great Plains, we determined the effects of grazing pressure on the efficiency of grazing. Under Objective A.2. (Determine impact of livestock grazing, fire, mechanical treatments, and drought on ecological integrity and watershed structure and function), we made significant progress in understanding the interactions of livestock grazing and fire on vegetation structure for grassland bird habitat, grasshopper abundance, cactus mortality, livestock and pronghorn antelope behavior and use patterns and livestock production responses. Collectively, results from these experiments addressing NP 215 Objectives A.1 and A.2 have been incorporated into a USDA AFRI Rangeland Research Program grant. Under Objective A.3. (Identify factors such as landscape position, species composition, land use history, management strategies, and climatic variables that can be used to predict and minimize the risk of degradation of rangeland ecosystems) we made progress to determine the influences of ecological sites, topography and water availability, with the latter two through the topographic wetness index and NDVI, on livestock production across large spatial scales (>16,000 acres). Under Objective B.1. (Develop monitoring and decision-support tools and management strategies for land managers), we made substantial progress in the application and transfer of developed technology of field- and remotely-sensed image acquisition and subsequent image analyses. We used very-large scale aerial imagery on several arid and semi-arid rangelands in the western US for assessments of shrub density, critical wildlife habitat, and influences of prescribed fire on bare soil. Under Objective C.1. (Understand mechanisms of weed invasion and develop management strategies that can be used to restore rangelands that have been degraded by weeds and other disturbances), we made substantial progress regarding the influence of extreme events on weed invasion, and the influence of global change (atmospheric carbon dioxide and increased temperatures) on native and non-native pairs of weedy species. Additionally, Unit scientists completed their involvement in literature assessments regarding the effectiveness of major conservation practices employed on private lands through the USDA-Natural Resources Conservation Service (NRCS) Rangeland Conservation Effects Assessment Program (CEAP) which is scheduled to be released early this fall.
1. Improved grazing efficiency measures for the Great Plains. Many individual grazing studies have been conducted evaluating livestock and vegetation responses to livestock stocking rate in the North American Great Plains. Comparisons across these studies are limited by lack of consistency in the terms light, moderate and heavy grazing at individual sites. ARS scientists in Cheyenne, WY, Fort Collins, CO, and Mandan, ND, in collaboration with university scientists from South Dakota State University, Texas A&M University-Kingsville, North Dakota State University, Kansas State University, and the University of Nebraska-Lincoln, calculated forage allowances to facilitate across site comparisons for 6 long-term studies in various states. The scientists determined that harvest efficiency of the livestock grazing was 42, 26, and 16% for heavy, moderate, and light stocking rates, respectively. The amount of forage on offer was not linear with either grazing or harvest efficiency resulting in increased efficiencies at low forage allowances and decreased efficiencies at high forage allowances. Using forage on offer to “standardize” stocking rates across rangeland ecosystems should facilitate increased communications among scientists, management agencies, land managers and the public regarding this primary rangeland management practice for production and conservation goals.
2. Production-conservation issues related to a species of concern. The mountain plover is a species of significant conservation concern in the western Great Plains. An ARS scientist in Cheyenne, WY, and Fort Collins, CO, collaborated with the US Forest Service Pawnee National Grassland to evaluate habitats selected by mountain plovers in order to inform potential grazing and fire management strategies for this species. The Pawnee National Grassland was historically considered a key breeding stronghold for this species in the United States, prior to dramatic population declines that occurred over the past 4 decades. The ARS scientist demonstrated that while mountain plovers are rare in moderately-grazed rangeland that comprises most of the region, mountain plovers occur at high densities on recent prescribed burns and active black-tailed prairie dog colonies. Research indicates that disturbances such as fire and prairie dogs combined with moderate grazing are needed to address production-conservation issues in western Great Plains.
3. Costs and risks with subdividing pastures on rangelands. One of the most common practices used on rangelands for management is subdividing pastures by adding additional fences to provide management flexibility, intensify management, and increase more uniform use of pastures. An ARS scientist in Cheyenne, WY, and Fort Collins, CO, in cooperation with a private consultant and the Environmental Defense Fund determined materials and installation costs, longer-term maintenance costs of these fences, and the influence of public financial incentives through the Farm Bill on total costs and financial risk to the land manager. Researchers estimated livestock stocking rates would need to be increased 9-16% over twenty years to maintain break-even conditions. These increased stocking rates could reduce the health of rangelands and decrease animal and plant productivity.
4. Seasonal livestock gains with cool-season forages in shortgrass steppe. In the western Great Plains, forage gaps in the early spring and late fall exist for livestock producers due to the high dominance of warm-season grasses and lack of cool-early season grasses. ARS scientists in the Cheyenne, WY, and Fort Collins, CO, in cooperation with the Crow Valley Livestock Cooperative evaluated livestock gains of young beef cows on two different cool-season forage grasses (crested wheatgrass and Russian wildrye) in the shortgrass steppe. Three-fourths or more of the annual cow weight gain on these grasses was obtained with spring grazing, whereas gains were much less from the fall grazing. Beef production on these cool-season forages was two to four times greater than native vegetation. These cool-season forages can fill the seasonal gaps in forage availability in this region and enhance total economic returns for beef producers.
5. Bare ground promotes erosion. Percent bare ground is a measure the amount of soil surface exposed to the erosive impact of rain and wind, and is therefore an important indicator of the ecological health of rangelands. An ARS scientist in Cheyenne, WY, and Ft. Collins, CO, collaborating with Bureau of Land Management in Wyoming discovered new evidence that the line-point intercept, a commonly used rangeland health monitoring method, undervalues the amount of bare ground measured. They also found that a new image-based method provides a verifiable measure of bare ground that can be accurately used to assess long-term ecological trends. Image-based monitoring methods are replacing, or being used with, line-point intercept in many rangeland-monitoring situations and the image-based methods are now taught to natural resource students in several western state universities.
6. Natural enemy accumulation on introduced plants over four centuries. Loss of natural enemies is thought to be one of the primary reasons that plants from other continents become invasive, but such enemy release is expected to erode over time as plants acquire new enemies. An ARS scientist in Cheyenne, WY, and Fort Collins, CO, in collaboration with scientists from the University of North Carolina and the Czech Republic showed that while plants introduced centuries ago are infected by more diseases than recently introduced plants, they still support only a small fraction of the diseases they supported in their native range. These results suggest at time scales relevant to management, enemy release will continue to give invasive plants an advantage over native plants, and augmentation of natural enemies through biological control will remain a relevant management technique.
7. Value of grazing-tolerant mixed-grass rangeland. Designing sustainable rangeland management strategies requires an understanding of how grazing influences plant invasion. The invasive plant dalmatian toadflax reduces both forage quality for livestock and biological diversity in much of western North America, and has been observed to invade following overgrazing. Using aerial imagery and novel spatial statistics, ARS scientists in Cheyenne, WY, and Fort Collins, CO, in collaboration with scientists from the Animal and Plant Inspection Service and Colorado State University, discovered that Dalmatian toadflax is actually less likely to invade areas with higher grazing intensity in rangelands containing a mixture of native grass species. These results suggest that rangelands with a diversity of native grass species which are tolerant to grazing will be more resistant to invasion, and that grazing can be a powerful tool in limiting plant invasion.Mitchell, C.M., Blumenthal, D.M., Jarosik, V., Puckett, E.E., Pysek, P. 2010. Controls on pathogen species richness in plants introduced and native ranges: roles of residence time, range size and host traits. Ecology Letters. 13:1525-1535.