Location: Range and Livestock Research2013 Annual Report
1a. Objectives (from AD-416):
Objective 1: Develop strategies and decision tools to proactively manage livestock grazing, fire, and drought impacts on Great Plains community structure and function. Sub-objective 1.A. Determine plant community and livestock response to post-fire grazing deferment. Sub-objective 1.B. Determine plant community response to fire return interval and seasonality. Sub-objective 1.C. Determine patch burning effects on plant community dynamics, animal performance, grazing distribution, and foraging efficiency. Sub-objective 1.D. Characterize grazing history effects on rangeland integrity and stability. Objective 2: Improve animal productivity and product quality based on predicted nutrient intake, forage dynamics, and diet selection processes in the northern Great Plains. Sub-objective 2.A. Determine effects of forage quality on autumn forage intake as it interacts with cow lactation and gestation status. Sub-objective 2.B. Determine rumen microbial response to noxious weed consumption by sheep and cattle. Objective 3: Develop management strategies to restore rangelands degraded by weeds and prevent weed invasions in the northern Great Plains. Sub-objective 3.A. Determine interacting effects of fire and grazing on annual brome dynamics. Sub-objective 3.B. Provide weed management protocols adjusting for inter-annual variation. Sub-objective 3.C. Develop an internet-available system to quantify site-specific invasive weed impacts. Sub-objective 3.D. Develop grazing strategies to reduce invasive weed population growth rates.
1b. Approach (from AD-416):
The planned research is designed to improve sustainability of rangeland production by addressing the interacting effects of disturbances on stability and integrity of rangelands and efficiency of livestock nutrient conversion. Objectives are to: 1) Develop strategies and decision tools to proactively manage livestock grazing, fire, and drought impacts on Great Plains community structure and function; 2) Improve animal productivity and product quality based on predicted nutrient intake, forage dynamics, and diet selection processes in the northern Great Plains; and 3) Develop management strategies to restore rangelands degraded by weeds and prevent weed invasions in the northern Great Plains. Experiments are integrated across objectives and will determine the interacting effects of grazing, fire, drought, and invasive plants on plant communities (production, species composition, diversity, heterogeneity, propagation, and survival) and the effects of changes in vegetation and animal physiology on livestock (weight gain, distribution, diet quality, diet selection, diet diversity, foraging efficiency, forage intake, and rumen microbial diversity). Two experiments are replicated across three locations (Miles City, MT, Nunn, CO and Woodward, OK) to determine ecological ramifications of fire seasonality, return interval, and grazing interactions in semiarid rangelands on a north-south gradient across the western Great Plains. Understanding the mechanisms that control disturbance effects on rangelands and animal responses to alterations in the plant community will promote development of proactive management strategies for improved stability in rangelands and rangeland livestock production systems.
3. Progress Report:
First cycle of fire season and frequency experiments was completed, and data from expansion of the study were collected for soil microbial DNA and RNA, and grass axillary bud dynamics. Long-term livestock exclusion data were collected and a portion of the data are being written up in a collaborative effort with Colorado State University. Final data were collected and are being analyzed for two mine restoration projects.
1. Fire and defoliation effects on purple threeawn grass and competing species. Purple threeawn is a competitive native perennial grass with monoculturistic tendencies and poor palatability. ARS researchers in Miles City, MT examined effects of fire, defoliation, and interspecific/intraspecific planting for threeawn blue grama and western wheatgrass production of biomass, tillers, and axillary buds. Researchers determined that threeawn is sensitive to fire, with 36% mortality and a 27% reduction in productivity for surviving plants. Fire limited future production capacity of threeawn by reducing axillary bud production of surviving plants 25%. Fire reduced threeawn from 60% to 23% of the total biomass when grown with blue grama or western wheatgrass, indicating good potential for rapid reductions in threeawn dominance and restoration of plant diversity with fire.