Elevated forest canopy loss after wildfires in moist and cool forests in
the Pacific Northwest
Abstract
Wildfire frequency, intensity, and severity are increasing across the
Western U.S. Significant tree mortality can occur years after fire
events, but this has received little attention compared to the immediate
tree loss during a fire. We overlapped forest cover loss data with burn
severity maps in the U.S. Pacific Northwest and quantified the total and
delayed forest canopy loss after fires. We found that wildfires resulted
in total canopy losses of 89%, 67%, and 31% within three years in
areas burned at high, moderate, and low severity, respectively. The
delayed canopy loss accounted for approximately 1/3, 1/2, and 2/3 of the
total canopy loss for high, moderate, and low severity burns. Delayed
canopy loss was greater in moist and cool areas than in dry and warm
areas, possibly because tree species in the wetter areas are less
adapted to tolerate fires with traits such as bark thickness and crown
height. Across all forests, delayed canopy loss was greater in dry and
warm years. These results suggest greater canopy losses will occur as
wildfires expand into areas that historically experienced infrequent
fires.