Project Description
Big sagebrush (Artemisia tridentata) rangelands are very widespread across the western U.S. and provide a variety of economic and cultural benefits including livestock grazing, recreational opportunities, and energy development. However, the long-term sustainability of these benefits is threatened by the combined impacts of altered wildfire regimes, invasive annual grasses, and increasingly severe drought. Although ranching operations are increasingly threatened by these changes, strategic use of livestock grazing may be a powerful tool for combating invasive species and decreasing wildfire risk. This project is exploring the potential to use grazing as a tool in coming decades to help sustain sagebrush rangelands and the benefits that they provide.
Objectives:
Broadly, our goal is to understand how livestock grazing interacts with wildfire and climate change in big sagebrush rangelands.
Specifically, we are working on addressing the following questions:
What is the long-term (current and future) impact of livestock grazing in the big sagebrush region on biomass by plant functional type (sagebrush, perennials, annuals) and on sagebrush ecological integrity?
How and where can changing grazing intensity be used to reduce current and future fire probability and what does that mean in terms of the proportion of the landscape in early vs late successional stages?
What is the trade-off between the potential positive impacts of increased grazing intensity for suppressing fire and negative impacts on ecological integrity through decreasing biomass of desirable plants?
Approach:
We used the individual-based simulation model STEPWAT2 to estimate how the abundance of key plant functional types (sagebrush, herbaceous perennials, and herbaceous annuals) and wildfire frequency may change under future climate conditions and how those changes are influenced by livestock grazing intensity. In the model Wildfire frequency was determined by recent climate and the quantity of fine fuels. We integrated simulation output with remotely sensed data to calculate sagebrush ecological integrity, an index that incorporates desirable components (sagebrush, perennials) and undesirable components (annuals, conifers, and human modification) of sagebrush ecosystems.
Outcomes
We are still actively working on this research and do not yet have finalized results.
Our preliminary results (not yet peer reviewed and not for citation) suggest that across the sagebrush region, simulated increases in grazing intensity tended to reduce wildfire frequency but also lowered sagebrush ecological integrity (SEI; an index of ecological integrity based on abundance of desirable native plant groups and ecosystem threats), providing evidence for a potential management trade-off (Fig. 1). The strength of this trade-off varied geographically, with increased grazing causing large reductions in wildfire frequency in the western portion of the sagebrush region with more limited SEI losses, especially in Other Rangeland Areas (areas with low SEI). In contrast, in the east, grazing had limited effect on already low wildfire frequency but caused declines in SEI. Our preliminary results suggest that a similar trade-off between the positive effects of grazing for wildfire mitigation, and potential negative effects on SEI also occurs under future climate conditions. Wildfire frequency tended to increase, especially in the western portion of the region, under future climate conditions. Overall, our preliminary results indicate that grazing may be an important climate adaptation tool especially in areas with high (and likely increasing) wildfire, but there is a need to also consider the impacts of grazing on ecological integrity caused by reductions in abundance of desirable plant groups such as perennial grasses and sagebrush.
More coming soon...
Collaborators
Alex Kumar & Geoff Bedrosian- U.S. Fish and Wildlife Service
William Lauenroth - Yale University, School of the Environment,
Kyle Palmquist - Marshall University, Department of Biological Sciences
John Tull - USGS Southwest Climate Adaptation Science Center
Support
U.S. Fish and Wildlife Service, Bureau of Land Management, USGS Ecosystems Mission Area, and the USGS Climate Adaptation Science Centers