Grazing Effects on Fuels Vary by Community State in Wyoming Big Sagebrush Steppe

Abstract

Limiting fire in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) steppe is often a management priority as fires threatens its ecological integrity and rural economies that depend on it. However, the Wyoming big sagebrush steppe is vast and occurs in different community states from intact (sagebrush-bunchgrass dominated) to exotic annual grass dominated. Grazing has been suggested as the only tool that is likely feasible to apply across such large landscapes to manage fine fuels, but there is concern that over time grazing may induce undesirable shifts in plant community composition (e.g., increases in exotic annuals) that increase fire risk. Therefore, we evaluated the longer-term (+10 yr) effects of contemporary, moderate grazing by cattle compared with grazing exclusion on fuel characteristics in three community states: intact, degraded, and exotic annual grass states. We accomplished this by measuring fuel characteristics in five grazed and ungrazed areas in each community state in 2020 and 2021. Grazing generally decreased fine fuel continuity and biomass and increased the live-to-dead ratio. These fuel alterations are consistent with decreasing the probability of fire ignition and, if ignited, producing a slower spreading fire with shorter flame lengths. The response of several fine fuel characteristics to grazing varied by community state. Fine fuel characteristics also commonly varied among community states and between years. These results suggest that fuel management plans need to recognize that grazing effects will vary by community state and be flexible because fuel characteristics vary spatially and temporally. Overall, our results suggest that contemporary grazing in the Wyoming big sagebrush steppe reduces the probability of wildfire and likely increases the effectiveness and safety of fire suppression. Consequently, grazing exclusion in these communities increases the probability of frequent, large wildfires that are difficult and dangerous to suppress.