Impacts of livestock grazing on wildfire probability vary by region and vegetation type in California

Background/Question/Methods

Wildfire activity has increased in California in recent decades, impacting ecosystem composition and functioning, as well as human well-being. California’s rangelands are complex social-ecological systems composed of multiple fire-adapted ecosystems (e.g., grasslands, chaparral and shrublands, and woodlands) and the people who live and work in them. Livestock grazing has been proposed as a tool for reducing wildfire activity in these rangeland systems. We analyze how grazing affects wildfire at large spatial scales, assessing wildfire probability on rangelands with different grazing levels. We collected grazing data by surveying 140 large private rangeland landowners in three social-ecological regions defined by ecoprovinces and administrative boundaries: California’s North Bay, Central Coast, and Central Valley and Foothills. Using pre-regression matching and mixed effects regression, we calculate the wildfire probability from 2001-2017 in each region in grasslands, shrub/scrublands, and forests.

Results/Conclusions

We find that in the Central Coast and North Bay social-ecological regions, wildfire probability decreases as stocking levels increase in grasslands, shrub/scrublands, and forests, with reductions of 31.0-76.5%. In the Central Valley and Foothills, the relationship is complex, with wildfire probability increasing over some grazing levels and significant variation in the effects of higher stocking densities. Our results indicate that in some regions and ecosystems in California, livestock grazing can reduce annual burn probability, providing the first large-scale assessment of this relationship and suggesting that targeted grazing in certain locations and vegetation types may be a tool for reducing the effects of changing fire regimes on ecosystems and humans.