Location:2010 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.1, 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 through interactions of grazing, prescribed fire and prairie dogs as a focal aspect of managing for both production and conservation goals on arid and semi-arid rangelands. 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 NIFA planning 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 topography and water availability, 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 very-large scale aerial imagery on arid and semi-arid rangelands in the western US. Progress was made in assessing critical wildlife habitat, determinations of revegetation success on dramatically disturbed lands such as pipelines, modifications in stream morphology following changes in grazing management on riparian areas, and efficacy of herbicide control efforts on large scales addressing invasive weeds. 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 efficacy of restoring competitors and natural enemies for long-term control of weed invasion, the understanding of the synergy between availability of resources and natural enemies in weed invasion, and the contribution of carbon addition to reduce establishment of invasive weeds. Additionally, Unit scientists continue to be highly involved in literature assessments and monitoring efforts 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).
1. Managing for biodiversity and livestock – promotion of vegetation heterogeneity. Rangelands that differ in structure and composition of vegetation can support a greater number of plant and animal species. Management strategies should strive to maintain (or increase) differences in structure and composition of vegetation to increase habitat diversity for wildlife, improve overall rangeland health, and help recover declining grassland bird populations. ARS scientists in Cheyenne, WY and Fort Collins, CO, in cooperation with the Environmental Defense Fund, Rocky Mountain Bird Observatory and Wyoming Game and Fish outlined an approach that aids decision making for land managers at different spatial scales to maintain or improve differences in structure and composition of vegetation. This approach provides identification of appropriate scales at which to address differences in structure and composition of vegetation for land managers, suggests important management considerations, and indentifies land management practices that can improve structure and composition of vegetation at the different spatial scales.
2. Fire-grazing interactions in shortgrass steppe. Prescribed burning programs have recently been implemented on five National Grasslands encompassing >1 million acres of public rangelands in the western Great Plains to enhance wildlife habitat, control unpalatable plant species, and restore historic disturbance regimes. However, livestock producers have been concerned about potential negative consequences for forage production, and whether grazing may need to be deferred during the first year after a fire. ARS researchers in Fort Collins, CO, and Cheyenne, WY, along with a collaborating scientist from Colorado State University, studied the interactive influence of fire and grazing on soil moisture, soil nitrogen, and plant growth in shortgrass steppe in northeastern Colorado. Burning had no influence on forage production or soil moisture in the first post-burn growing season, but did enhance digestibility of blue grama forage in late May. No differences in herbaceous plant production were found between sites that were burned and grazed in the previous year versus sites that were burned and protected from grazing. This study indicates that dormant-season prescribed burns can have neutral or positive consequences for livestock production due to a neutral effect on forage quantity and a short-term enhancement of forage quality. In addition, the study showed that with conservative stocking rates, deferment of grazing during the first post-burn growing season is not necessary to sustain plant productivity.
3. Interseeding legumes in sagebrush-dominated rangelands. The improvement practice of interseeding legumes (e.g., alfalfa) into rangelands has been widely evaluated in grass-dominated systems for increased forage production, higher nutritive quality of the forage and greater soil carbon and nitrogen. However, knowledge about the effects of this improvement practice in sagebrush-dominated systems are limited although there is increasing attention on this practice for improving critical wildlife habitat, especially for greater sage-grouse. ARS scientists in Cheyenne, WY, in cooperation with University of Wyoming scientists, evaluated plant community and small mammal population responses to disturbing 10% of the ground surface area to interseeding of yellow-flowered alfalfa in a sagebrush grassland. The disturbance associated with interseeding had little influence on plant community dynamics (production, species richness and diversity) and small mammal species richness indicating that interseeding legumes in sagebrush rangelands will have little negative consequences for ecosystem functioning.
4. Immobilizing nitrogen to control plant invasion. Nitrogen pollution has been shown to exacerbate plant invasion in many ecosystems. ARS scientists in Fort Collins, CO, and Logan, UT, in collaboration with Colorado State University scientists, compared management strategies for manipulating nitrogen availability and invasion. Effective management strategies were those that encouraged slow-growing native plants, which can immobilize nitrogen, and reduce the nitrogen available to invasive plants. Such management strategies include ecosystem restoration and, in some instances, grazing or burning. These research findings simplify the relationship between nitrogen pollution and invasive species management, and help land managers determine the feasibility of manipulating nitrogen to inhibit invasion by weeds.
5. Restoring competitors and natural enemies for long-term control of invasive plants. Managing invasive plant species in rangelands is challenging given the large areas involved and the low economic returns per unit area. Economically sustainable management strategies must therefore be effective over the long term. ARS scientists in Fort Collins, CO, in cooperation with University of Colorado and Colorado State University scientists, determined that biological control and ecosystem restoration can be highly effective regarding long-term control of invasive plants if these management strategies are used together. These findings can be widely used by land managers in determining how to control invasive plants in rangelands with changing environments.
6. Toward accurate sage-grouse counts. Conservation efforts for the greater sage-grouse require more data, as well as more accurate data, to determine population numbers. Current count methods are labor intensive and expensive, as well as spatially-limited. ARS scientists from Cheyenne, Wyoming, working with the wildlife conservation group Nevada Big Horns Unlimited, tested various ways of obtaining high-resolution aerial photography from which to make multiple lek counts in a single day. The group gained information on sage-grouse responses to low-altitude airplane approaches, and defined useful camera and lens combinations. This information is being used to propose alternative methods for obtaining aerial photographs of sage-grouse on leks.
7. High-resolution aerial surveys detect leafy spurge invasion fronts on wildland. Invasion by weeds is a leading threat to intact native plant communities on wildlands. Detection of weed invasions is often limited to roadside surveys but there is a pressing need to detect invasive weeds occurring in spatially small areas that are often diffuse in arrangement. Timely detection of these localized populations can help in efforts to preserve native plant communities as well as provide land mangers with earlier knowledge of presence of these weeds to increase control efforts. ARS scientists from Cheyenne, Wyoming, in cooperation with the Bureau of Land Management in Idaho, used a dual-camera aerial survey to determine leafy spurge occurrence and distribution, as well as relate distribution to associated vegetation and control efforts. Simultaneously obtaining images at 2 different resolutions with coordinated fields-of-view optimized leafy spurge detection capacity while retaining plant identification capability. Compared to current ground-based surveys, aerial surveys provide land managers an enhanced capacity for early detection of invasive weeds on wildlands.Blumenthal, D.M., Augustine, D.J. 2009. Plant Interactions With Herbivores. Encyclopedia of Life Sciences doi10.1002?9780470015902.a0003203.pub2.