Location: Range and Livestock Research2009 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
This report documents research conducted under the in-house project 5434-21630-002-00D, Proactive Management for Sustainable Rangeland Production. All milestones were primarily limited to treatment application and data collection during this reporting period. This project addresses goals outlined in the NP 215 Rangeland, Pasture and Forages Action Plan under Component I (Rangeland Management Systems to Enhance the Environment and Economic Viability) and supports ARS strategic plan Objective 5.1 (Provide Science-Based Knowledge and Education To Improve the Management of Forest, Rangelands, and Pastures). More specifically, experiments in this project target the following objectives of the NP 215 Action Plan: Objective A.2, Determine impact of livestock grazing, fire, mechanical treatments, and drought on ecological integrity and watershed structure and function; Objective B.1, Develop monitoring and decision-support tools and management strategies for land managers; Objective B.4, Assess near- and long- term animal productivity, well-being and product quality under alternative rangeland management strategies; and 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. Portions of this project are related to or coordinated with research in NP 304 Crop Protection and Quarantine (weed biology and ecology; plant, pest and natural enemy interactions and ecology).
1. Fire Reduces Emergence of Invasive Plant Seeds. Common rangeland weed control methods rarely affect the ability of weeds to grow from seed already deposited. Seeds of Japanese brome, spotted knapweed, Russian knapweed, and leafy spurge were deposited on the soil surface and subjected to fire at six fuel loads common to grasslands and a non-burned control. Seedling emergence was reduced 79-88% with fuel loads common to the western Great Plains, at least 97% with fuel loads common to the central Great Plains and emergence probabilities were less than 1% for all species but spotted knapweed with fuel loads typical of the eastern Great Plains. Results indicate high potential for fire to disrupt the life cycle of invasive species through direct seed mortality. The relationship between fuel load and seedling emergence provides good predictability of fire effects on surface-deposited seeds. Abrupt reductions in seedling emergence with relatively light fuel loads indicate fire can increase mortality of invasive plant seed across a broad range of habitats.