Observed and Expected Increases in Fire Severity Weaken Stabilizing Feedbacks that Promote Forest Resilience

Abstract:

Increases in burned area across the western US since the mid-1980’s have been widely documented and linked partially to climate factors, yet parallel evaluations of trends in fire severity are lacking. Here, we evaluate fire severity trends and their interannual relationships to climate for western US forests from 1985-2017. Significant increases in annual area burned at high severity (AAB_hs) were observed across most ecoregions, with an overall eight-fold increase in AAB_hs across all western US forests. The strong links we found between the annual fire severity metrics and climate, as well as the observed and projected trend toward warmer and drier fire seasons, suggest that climate change will contribute to increases in fire severity in future decades. The increasing prevalence of high-severity fire in western US forests may weaken stabilizing feedbacks that historically promoted ecosystem resilience. Diminished resilience of forests to wildfire may lead to extensive areas of altered vegetation across the western US and beyond.