Grazing, wildfire & climate change in sagebrush rangelands

Big sagebrush (Artemisia tridentata) dominated ecosystems are widespread across the western U.S. and face combined threats from invasive annual grasses, altered wildfire regimes, and climate change. Livestock grazing is the most pervasive land use practice within sagebrush ecosystems. As a result, grazing has the potential to be used to help minimize the combined threats of wildfire and invasive plants, although the effectiveness and appropriateness of grazing under future climate conditions remain unclear. 

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.