Livestock grazing as a tool to sustain big sagebrush rangelands

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: 

1. 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? 

2. 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?

3. 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.