Location:2013 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:
Key findings for this project over the 5 years include: (1) Grazing strategies and forage/animal production in semi-arid rangelands: Results showed that weather variation and stocking rate affect vegetation and animal responses. Grazing system (rotational vs. season-long) did not influence results. Both forage and livestock production is reduced with increasing stocking rate. Livestock weight gains per unit land area increased with increasing stocking rate. Results do not support rotational grazing enhancing either forage/cattle production or environmental goals on rangelands. However, results do not effectively address all potential management benefits arising from rotational grazing systems. Rotational grazing studies have seldom been investigated as a component of the entire ranch enterprise and rarely incorporate the social/human component of grazing management. (2) Using Livestock as Ecosystem Engineers in rangelands: Management practices for rangelands have largely emphasized livestock production and uniform use of vegetation, but ecosystem services desired by society and contemporary conservation objectives may not be achieved with these traditional management practices. Use of livestock as tools to alter structure and function of rangelands can improve habitat for declining native grassland birds in the western Great Plains. Rangelands that differ in structure (plant height) 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. (3) Rangeland Biodiversity: Management Practices to Enhance Rangeland Wildlife Habitat while Sustaining Livestock Production. Fire and black-tailed prairie dogs (Cynomys ludovicianus) have been widely suppressed in the western Great Plains over the past century, primarily due to potential impacts on forage and livestock production. More recently, fire and prairie dogs have been recognized as key factors influencing habitat for declining wildlife species in the region. Although forage production does not change with burning, short-term improvement of forage quality is possible. In addition prescribed burns provide preferred nesting habitat for the mountain plover (Charadrius montanus), enhance habitat for the swift fox (Vulpes velox), and can be used to enhance expansion rate of black-tailed prairie dog colonies. Livestock gains do not decrease on pastures with patches burned, but they do decline with increasing percentage of the pasture colonized by prairie dogs. These studies have quantified tradeoffs between management for livestock versus some declining wildlife species, and provide insights to landscape-scale management patterns that can be used to minimize conflicts in managing rangelands for multiple ecosystem services. Research will continue in replacement project #5409-22610-001-00D.
1. Seasonal weather effects on livestock production. Seasonal weather conditions (precipitation and temperature) impact beef production on rangelands and knowledge of how and when impacts occur would assist ranchers in selecting stocking rates that will be most profitable based on weather conditions. ARS scientists in Cheyenne, WY/Fort Collins, CO, Mandan, ND, and Miles City, MT used three decades (1982 – 2011) of weight gains data from yearling steers to study how spring (April – June) and summer (July – September) temperature and precipitation impact beef production. Heavy stocking rates were more sensitive than light stocking rates to seasonal weather variation. Cool, wet springs and warm, wet summers were best for beef production at moderate and heavy stocking rates. Results will be used in decision support tools to help ranchers decide stocking rates based on forecasted seasonal weather conditions from the National Oceanic and Atmospheric Administration (NOAA).
2. Natural resource goals and management practices of ranchers. What natural resource goals do Wyoming ranchers have for rangelands, and what management practices are used in an attempt to achieve these goals? ARS scientists in Cheyenne, WY/Fort Collins, CO, in cooperation with scientists from the University of California-Davis, the University of Wyoming, and the Wyoming Stock Growers Association (WSGA) used data from a survey of WSGA producer members to answer these questions. Livestock production and forage production were the primary management goals, with secondary goals of soil health and water quality. Most of the ranching operations grazed cow-calf pairs and moved livestock among two or more pastures after less than three months in each pasture. Many ranchers also had other resource activities on their ranches including hunting, conventional energy development, and other agricultural production. Wyoming ranches are diverse in operation characteristics and management practices, and may represent a challenge for policy makers designing programs and incentives to increase conservation benefits from rangelands.
3. Livestock effects on the redistribution of soil nitrogen in shortgrass rangeland. Soil nitrogen availability can strongly influence the quality of forages for livestock grazing semiarid rangelands. ARS scientists in Cheyenne, WY/Fort Collins, CO collaborated with a scientist from Colorado State University to examine how cattle influence losses of nitrogen from shortgrass rangeland through multiple pathways. These pathways include export of nitrogen as beef, redistribution of nitrogen from plants in grazed areas to areas where animals gather (around water points, corners of pastures), and losses of nitrogen from urine. Pathways of nitrogen losses associated with cattle may explain the imbalance between current estimates of atmospheric inputs and trace gas losses of nitrogen from these rangelands. Management practices to reduce these pathways of nitrogen loss can influence long-term sustainability of semiarid rangelands.
4. Assessment of cattle grazing behavior with GPS collars. The ability to measure when and where cattle are grazing would provide valuable information about the distribution of grazing in rangelands. ARS scientists in Cheyenne, WY/Fort Collins, CO showed that collars containing a global positioning system (GPS) can successfully be placed on cattle to measure where and when they are grazing, resting and travelling. Findings demonstrate that this technology can be used to accurately quantify how grazing management practices affect the duration and location of cattle grazing at hourly to monthly time scales.
5. The influence of prairie dogs on biodiversity and livestock production in the western Great Plains. Black-tailed prairie dogs (Cynomys ludovicianus) are widely viewed as competitors with cattle, but they are also important for biodiversity conservation because they create habitat for other native species. ARS scientists from Cheyenne, WY/Fort Collins, CO and Woodward, OK examined the effects of prairie dogs on the nutritive value and amount of forage in multiple sites in the western Great Plains. Prairie dogs had large negative effects on cattle energy gain during periods of below-average precipitation. However, these effects could be partially or fully offset during periods of above-average precipitation through increased digestibility of forage on prairie dog colonies. These results show that balancing livestock production and biodiversity conservation in these rangelands involves considering competitive effects on livestock during dry periods with low forage availability, benefits to cattle grazing on prairie dog colonies during wet periods, and habitat created by prairie dogs for species of conservation concern.
6. Evolution of weediness in invasive mullein. Rapid evolution may help invasive plants succeed in their new range, but it is unclear which traits evolve and how common such evolution is. Scientists from ARS (Fort Collins, CO), in cooperation with scientists from Colorado State University, discovered that common mullein, a Eurasian plant that is invasive in much of the United States, has evolved several traits typical of weedy and invasive species. These traits include low root-to-shoot ratio, rapid growth, and responsiveness to high water availability. U.S. mullein populations were also more resistant to a generalist insect herbivore. These results will help scientists and managers understand the role of evolution in invasion, and develop management strategies, such as increased competition from desired species, to combat species with such new evolved weedy traits.
7. Invasive species performance across ranges. The idea that invasive species perform better in their invaded than their native range is central to the field of invasion biology, but has rarely been tested. A global collaborative effort, including scientists from ARS (Ft. Collins, CO), used meta-analysis to learn that across 53 problematic animal and plant invaders performance was higher in their invaded range, as measured by increases in size, abundance, or fecundity. Within that group, however, there were many examples of invaders that performed similarly across ranges. These results indicate that distinct behavior among ranges is common to, but not required for invasiveness. They will help scientists predict when range-specific management, such as biological control, is most likely to successfully control invasive species.
Weber, K.T., Chen, F., Booth, D.T., Raza, M., Serr, K., Gokhale, B. 2013. Comparing two ground-cover measurement methodologies for semiarid rangelands. Rangeland Ecology and Management. 66(1):82-87.