Area burned by severe fire has increased 8-fold in western U.S. forests over past four decades — increased probability that forests will convert to alternative vegetation types?

The physical and ecological effects of wildfire (hereafter fire severity) have important consequences in terms of soil erosion, carbon storage, forest succession, wildlife habitat, and human safety and infrastructure. This study evaluated changes in fire severity in western US forests from 1985 to 2017 and tested whether fire severity varied with fire‐season climate. Results show that area burned at high severity increased across most of the study area, with an overall eightfold increase in western US forests from 1985 to 2017. Furthermore, warmer and drier fire seasons corresponded with higher severity fire, indicating that continued climate change may result in increased fire severity in future decades. One potential consequence of greater area burned at high severity is an increased probability that forests will convert to alternative vegetation types. Our findings provide some guidance to managers as society struggles to better coexist with fire. For example, it may be possible to increase the prevalence of low‐ and moderate‐severity fire, sometimes referred to as “good fire,” through thoughtful planning about where and when to implement a less aggressive fire suppression response. Similar to prescribed fires that promote forest resilience, unplanned fires that burn during less‐than‐extreme fire seasons have the potential to serve as effective “fuel treatments.”

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