Prescribed fire, managed burning, and previous wildfires reduce the severity of a southwestern US gigafire

In many parts of the western United States, wildfires are becoming larger and more severe, threatening the persistence of forest ecosystems. Understanding the ways in which management activities such as prescribed fire and managed wildfire can mitigate fire severity is essential for developing effective forest conservation strategies. We evaluated the effects of previous fuels reduction treatments, including prescribed fire and wildfire managed for resource benefit, and other wildfires on the burn severity of the 2022 Black Fire in southwestern New Mexico, USA. The Black Fire burned over 131,000 ha in mostly low- to middle-elevation ponderosa pine and mixed conifer forests, but burned only ~4 % at high-severity, leading us to question what factors led to this fire burning in such an ecologically beneficial way and aligning with the natural range of variation in terms of burn severity for this region. In a landscape scale analysis, we found that areas that experienced more prescribed fire, wildfire managed for resource benefit, and wildfire (hereafter ‘treated area’) best explained patterns of burn severity in the 2022 Black Fire, outweighing the importance of fire weather and vegetation factors. A fully treated area experienced 51 % less high severity fire than an untreated area, on average, across the Black fire landscape. In a fine-scale fire progression analysis, we found that high-severity fire that encountered a previously treated area experienced a 21-55 % decrease in burn severity within 250 m of the treated area boundary. In sum, we found that previous treatments and wildfires that occurred within the Black fire perimeter were highly effective in influencing patterns of burn severity and appear to be the reason why the Black fire was restorative, and not catastrophic. Our results suggest that the severity of other large fire events can be reduced by increasing the pace and scale of treatment activities within low- and middle-elevation pine and mixed conifer forest landscapes.