Forest canopy cover affects microclimate buffering during an extreme heat event

Increasing temperatures and extreme heat episodes have become more common with climate change. While forests are known to buffer increasing temperatures (relative to non-forested areas), whether this buffering is maintained under extreme temperature events is relatively unknown. Here we assess whether forests continue to buffer microclimate (specifically temperatures) during an extreme heat event: the Pacific Northwest (PNW) heat dome in June 2021. We use a combination of ground-based and regional climate data and find that forest understories were 3 degrees C cooler than a clear-cut area and 4 degrees C cooler than regional temperatures during the PNW heat dome. By examining forests with different levels of canopy cover we also found that the buffering capacity of forests is greater under denser canopies even under extreme heat events. Additionally, we found vertical variation in thermal buffering, with the greatest amount of buffering at the surface of the forest floor. Overall, our findings suggest that temperate coastal forests, that are known to buffer average temperatures, can also act as microclimate buffers during extreme heat events like the heat dome that occurred in the PNW in 2021. This could be good news for forest dwelling organisms that are sensitive to such extreme heat events.