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. 2023 Nov 28;120(48):e2312909120.
doi: 10.1073/pnas.2312909120. Epub 2023 Nov 20.

The 2020 to 2021 California megafires and their impacts on wildlife habitat

Jessalyn Ayars  1   2 , H Anu Kramer  3 , Gavin M Jones  1   2
Affiliations

The 2020 to 2021 California megafires and their impacts on wildlife habitat

Jessalyn Ayars et al. Proc Natl Acad Sci U S A. .

Abstract

Fire activity during 2020 to 2021 in California, USA, was unprecedented in the modern record. More than 19,000 km2 of forest vegetation burned (10× more than the historical average), potentially affecting the habitat of 508 vertebrate species. Of the >9,000 km2 that burned at high severity, 89% occurred in large patches that exceeded historical estimates of maximum high-severity patch size. In this 2-y period, 100 vertebrate species experienced fire across >10% of their geographic range, 16 of which were species of conservation concern. These 100 species experienced high-severity fire across 5 to 14% of their ranges, underscoring potentially important changes to habitat structure. Species in this region are not adapted to high-severity megafires. Management actions, such as prescribed fires and mechanical thinning, can curb severe fire behavior and reduce the potential negative impacts of uncharacteristic fires on wildlife.

Keywords: climate change; fire severity; megafire; wildfire; wildlife habitat.

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Conflict of interest statement

Competing interests statement:The authors declare no competing interest.

Figures

Fig. 1.
Fig. 1.
Wildfire distribution in California (USA). (A) Dark shading indicates 2020 and 2021 wildfires. Colored regions denote ecoregions, which are defined in B. A map of the continental United States with California highlighted is provided for context. (B) Square kilometers burned in the 2020 and 2021 wildfire seasons by ecoregion. (C) Annual area burned (2012 to 2021) in California by CBI4 fire severity class. Horizontal black lines represent the 25th (lower dashed line), 50th (middle solid line), and 75th (upper dashed line) quantiles of annual area burned in California from 1878 to 2011, representing a historical range of variability. The Inset histogram shows the distribution of 2020 to 2021 high-severity patch sizes in California compared to the estimated historical upper bound (black vertical dashed line). There was some overlap in fire footprints between 2020 and 2021 as well as across 2012 to 2021.
Fig. 2.
Fig. 2.
Quantity and quality of habitat burned in 2020 and 2021 (combined). (A) The 50 species with the highest proportion of their range burned at all fire severities, by taxon. The black series indicates the proportion of range burned at all fire severities, and the red series indicates proportion of range burned at high severity. Open diamonds represent California SGCN (hereafter special-status species). (B) Average proportion of range burned for special-status versus other species by taxa. Error bars indicate SE. Area burned was different between special-status and other birds and reptiles for all burn severities (P < 0.001), but not between special-status and other amphibians or mammals. (C) Number of special-status and other species by percent of habitat burned. Dots indicate the expected counts based on number of species in range burned categories. Observed counts were significantly different than expected (χ24 = 71.4, P < 0.001).
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