Extreme weather, forest structure, and burn severity: Insights from the Pacific Northwest’s 2020 Labor Day Megafires

Abstract

In 2020, six wildfires burned more than 1 million acres over the Labor Day weekend in Oregon. Jeremy Fried, a research forester with the U.S. Forest Service, Pacific Northwest Research Station, saw an opportunity to study how these wind-driven megafires affected forest structure and carbon storage, and how forest structure before the fires may have influenced fire severity.

With research fellows Sebastian Busby and Angela Klock, Fried developed a model that estimated wind speed when wildfire entered forest plots previously inventoried through the national Forest Inventory and Analysis program. They found that under the hot and very dry weather conditions of the Labor Day fires, forest structure influenced fire severity only when wind speeds were low (less than 5 miles per hour, for exam­ple). Tree survival in young stands was much lower than in mature forest when fire arrived with low wind speed. When winds were high, all stand age classes experienced high mortality.

The researchers also used postfire observations of soil and tree burn-severity to validate the accuracy of two com­monly used burn-severity map products derived from satellite data. The burn-severity maps were somewhat consis­tent with on-the-ground observations, but remote sensing can only detect fire effects on the overstory canopy, which aren’t always closely related to fire effects on soils and understory vegeta­tion and trees.

Citation

Watts, Andrea; Fried, Jeremy; Busby, Sebastian. 2026. Extreme weather, forest structure, and burn severity: Insights from the Pacific Northwest’s 2020 Labor Day Megafires. Science Findings 278. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 6 p.