PNNL

Abstract

The US Pacific Northwest has been experiencing increases in wildfire frequency, intensity, and severity. However, limited studies quantify forest losses immediately after wildfires (immediate forest loss) and in subsequent years (delayed forest loss) in temperate forests there. By overlapping forest loss data with burned severity maps, we detect forest losses in 89%, 67%, and 31% of forest areas burned at high, moderate, and low severity within three years, respectively. The fire-induced delayed forest loss ratio accounts for approximately 1/3 (28% delayed forest loss ratio compared to 89% total forest loss ratio), 1/2 (34% compared to 67%), and 2/3 (20% compared to 31%) of fire-induced total forest loss for high, moderate, and low severity wildfires, respectively. Across the Pacific Northwest, fire-caused forest loss exhibits large spatial variability, with higher forest loss occurring in moist and cool forests than in dry and warm forests. This may be because the moist and cool forests generally experience infrequent wildfires and thus lack fire-resistant traits such as thicker bark and higher crowns. Independent of spatial variations, delayed forest losses can increase by 2-3 times in drier and warmer years compared to wetter and cooler years. These spatial and temporal characteristics can be used to predict the variability of fire-induced forest loss in a warming climate.