Grazing Intensity Effects on Fire Ignition Risk and Spread in Sagebrush Steppe

Abstract

Wildfire activity is accelerating on many rangelands worldwide, yet the potential for grazing to be used as a fire management tool remains largely unknown. Particularly, little is known about the influence of grazing on ignition and initial spread of fire, as well as how these vary by differences in grazing management. We investigated effects of grazing intensity (light, moderate, high) on fuel characteristics, fire ignition, and initial spread during the wildfire season in a native-dominated shrub steppe in eastern Oregon. We found that differences in grazing intensity have differential effects on fuel profiles (cover, height, moisture, biomass) with resulting impacts on fire behavior, but these relationships varied across study years. In particular, grazing had a stronger effect on ignition probability in drier years. Fire behavior in lightly grazed plots were similar to ungrazed plots, while moderate grazing was similar to high-intensity grazing. Results of this study highlight that grazing can be useful as a tool for wildfire management, and grazing at moderate and high intensities can reduce the probability of fire propagation in native-dominated sagebrush ecosystems. Further, the effects of grazing are context dependent and therefore may depend on specific objectives and environmental conditions.