2012 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.
Under Objective A.1 (Develop management and monitoring strategies and decision-support tools that conserve natural resources while maintaining economic objectives), we contributed authorship to the evidence-based assessment of prescribed grazing practices for conservation benefits as part of the Rangeland Conservation Effects Assessment Program (CEAP) through the USDA-Natural Resources Conservation Service (NRCS). Assessments of tradeoffs between livestock production and provision of ecosystem services (e.g., wildlife habitat) continue with experimental efforts addressing management practices (grazing intensity, season of grazing, stocking rate, prescribed fire) and disturbances (prairie dogs) to blend production and conservation objectives. Under Objective A.2. (Determine impact of livestock grazing, fire, mechanical treatments, and drought on ecological integrity and watershed structure and function), we determined that prescribed fire and grazing by both cattle and prairie dogs provides sufficient habitat for a grassland bird that is a species of concern (Mountain Plover). Intensive grazing by cattle alone did not create suitable habitat, however. Collectively, results from these experiments have been incorporated into a USDA AFRI Rangeland Research Program grant involving collaborators from three universities (Texas A&M University, Colorado State University, and University of California-Davis). 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 determined that patchiness of bare soil occurs in grasslands of the western Great Plains at scales of 1-8 inches (scale of spaces between plants) and that increasing the frequency of these patches of bare soil may be an important early warning signal prior to the degradation of rangeland ecosystems. Under Objective B.1. (Develop monitoring and decision-support tools and management strategies for land managers), we collaboratively worked with the Agricultural Systems Research Unit to enhance the utility of the Great Plains Framework for Agricultural Resource Management (GPFARM) decision support tool for forage production and carbon and nitrogen cycling. In addition, we used very-large scale aerial imagery from over 15,500 acres of shortgrass steppe to create shrub density maps for several shrub and sub-shrub species. 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 contributed authorship to the scientific assessment of invasive plant management on anticipated conservation benefits as part of the Rangeland Conservation Effects Assessment Program (CEAP) through the USDA-Natural Resources Conservation Service (NRCS). Additionally, Unit scientists submitted a highly successful proposal to the ARS Long Term Agroecosystem Research Network, becoming one of the first ten sites in this new network.
Restoring historical disturbances to benefit grassland birds and possible conflicts with livestock production goals. Historically, both fire and grazing influenced vegetation structure and composition, and ecosystem functions, of the Great Plains. Land managers of the 20th century focused on reducing occurrence of fires and prairie dogs to promote livestock production. Subsequent declines in populations of many grassland birds have prompted land managers to consider restoring the disturbances of fire and prairie dogs to produce suitable habitat of grassland birds. ARS scientists in Cheyenne, WY/Fort Collins, CO studied nesting habitat of a grassland bird (Mountain Plover) in relation to prescribed fire and grazing by cattle with or without prairie dogs. Prescribed burning and grazing by cattle with prairie dogs are effective strategies to manage for Mountain Plover habitat. These management practices, however, have tradeoffs with regards to beef production associated with traditional grazing management strategies showcasing the difficulty in managing for both production and conservation goals.
Very high resolution aerial assessment of bare soil in grazed ecosystems. Spatial patterns of bare soil have been proposed as important ecological indicators of erosion, watershed function, wildlife habitat, and risk of invasive species. ARS scientists in Cheyenne WY/Fort Collins, CO collaborated with the US Department of Interior Bureau of Land Management to evaluate patterns of bare soil in grazed ecosystems with different intensities of livestock grazing. Using advanced remote sensing it was demonstrated that bare soil patches may be important early warning signals of the condition of grazed ecosystems. These signals can be used to target management action in a strategic manner to reduce risks of soil erosion, invasive plants and impaired watershed function.
The role of precipitation in controlling land-atmosphere fluxes of carbon dioxide. Predictions of how climate change is unfolding and possible societal actions to slow its development require quantitative information on the land-atmosphere fluxes of greenhouse gases. ARS scientists in Cheyenne WY/Fort Collins, CO, collaborated with Colorado State University scientists to find that precipitation events greater than approximately ½ inch promoted the net uptake of CO2 by shortgrass steppe vegetation and soils. However, smaller precipitation events caused a release of CO2 from the shortgrass steppe into the atmosphere. These results provide data for predictions of how weather patterns affect the exchange of CO2 between the land and atmosphere. The data highlight the importance of maintaining critical amounts of vegetation for the removal of CO2 and sequestration of carbon into the plant-soil ecosystem.
Evolution in invasive mullein. Rapid evolution is thought to help invasive plants succeed in new ecosystems, but it is unclear which traits evolve and how common such evolution is. ARS scientists in Cheyenne WY/Fort Collins, CO, collaborated with Colorado State University scientists to analyze multiple growth and defensive traits of common mullein plants from the species’ native and invaded ranges. Invasive North American mullein consistently grew larger than invasive mullein, and did not reduce investment in defensive traits. These results will help scientists and land use managers minimize the impacts of invasive species on rangelands.
An evidenced-based assessment of prescribed grazing practices. Experiments addressing prescribed grazing practices have been conducted for seven decades, yet synthesis of these findings for determination of conservation benefits for society is lacking. An ARS scientist in Cheyenne WY/Fort Collins CO, in collaboration with university scientists from Texas A&M University, Colorado State University, and the University of California-Davis determined that experimental grazing research has produced consistent relationships between stocking rate and plant production, animal production, and species composition of plant communities. Three major management recommendations and five areas requiring further research resulted from the study. This extensive evaluation of the published data relevant to grazing management provides the general public, private and public land managers, and policy makers with a current status of the conservation effects of prescribed grazing. The assessment can be used to develop strategies to achieve both production and conservation goals from grazed ecosystems.
Augustine, D.J. 2012. Response of native ungulates to drought in semiarid Kenyan rangeland. African Journal of Ecology. 48:1009-1020.
Booth, D.T., Cox, S.E., Simonds, G., Sant, E. 2012. Willow cover as a recovery indicator under a conservation grazing plan. Journal of Ecological Indicators. 18:512-519.
Augustine, D.J., Booth, D.T., Cox, S.E., Derner, J.D. 2012. Grazing intensity and spatial heterogeneity in bare soil in a grazing-resistant grassland. Rangeland Ecology and Management. 65:39-46.
Parton, W., Morgan, J.A., Smith, D.P., Del Grosso, S.J., Prihodko, L., Lecain, D.R., Kelly, R. 2012. Impact of precipitation dynamics on net ecosystem exchange. Global Change Biology. 28:915-927.
Briske, D.D., Derner, J.D., Milchunas, D.G., Tate, K. 2011. An evidence-based assessment of prescribed grazing practices. Book Chapter. In: D.D. Briske (ed.). Conservation benefits of rangeland practices: Assessment, recommendations, and Knowledge Gaps. United States Department of Agriculture, Natural Resources Research Service. pp. 21-74.
Toombs, T.P., Derner, J.D., Knight, B.K. 2012. Response to Barnes et al. Letter to the Editor (reference to Bracy Knight et al. 2011 paper in Rangelands). Rangelands. 34(1):40-41.
Sidle, J., Augustine, D.J., Johnson, D.H., Miller, S.D., Cully, J.F., Reading, R.P. 2012. Aerial surveys adjusted by ground surveys to estimate area occupied by black-tailed prairie dog colonies. Wildlife Society Bulletin. 36:248-256.
Baker, B., Augustine, D.J., Sedgwick, J.A., Lubow, B.C. 2012. Ecosystem engineering varies spatially: A test of the vegetation modification paradigm for prairie dogs. Ecography. 36(2):230-239.
Alba, C., Bowers, D., Blumenthal, D.M., Hufbauer, R. 2011. Evolution of growth but not structural or chemical defense in Verbascum thapsus (common mullein) following introduction to North America. Biological Invasions. 13:2379-2389.
Qi, Z., Bartling, P.N., Ahuja, L.R., Derner, J.D., Dunn, G.H., Ma, L. 2012. Development and evaluation of the carbon-nitrogen cycle module for the GPFARM-Range model. Computers and Electronics in Agriculture. 83:1-10.
Augustine, D.J., Derner, J.D. 2012. Disturbance regimes and mountain plover habitat in shorgrass steppe: Large herbivore grazing does not substitute for prairie dog grazing or fire. Journal of Wildlife Management. 76(4):721-728.