High-severity fire now dominant in California forests
Published in Proceedings of the National Academy of Sciences, 2026
Fire severity exerts crucial ecological controls in many forests globally. In California, where annual forest-fire area has increased dramatically in recent decades, understanding how burn severity is changing is essential for informing environmental policy and management. We developed a novel set of high-resolution maps of the Composite Burn Index (CBI) for 4,391 California forest fires from 1985–2024 and found that the proportion of forest area burned at high severity increased disproportionately rapidly, compensated by a significant decline in low-severity fire. These shifts were driven by increasing atmospheric aridity and preferentially occurred in high-biomass forests, greatly amplifying California’s total forest area burned by high-severity, largely stand-replacing fire over the past four decades.
Recommended citation: Hung, M.J. & Williams, A.P. High-severity fire now dominant in California forests. Proc. Natl Acad. Sci. USA (2026).
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