Salem, Oregon — New research using satellite imagery shows the 2021 Pacific Northwest heat dome caused severe canopy damage across Oregon and Washington, scorching nearly 5% of the region’s western forests — an area roughly the size of Rhode Island. The multi-day heat wave from June 25–29, 2021, pushed Portland to a record 116 degrees and caused dozens of deaths in Multnomah County. It also rapidly turned vast stretches of green forest canopy to red, orange, and brown as leaves burned and chlorophyll production collapsed.
The study, published Oct. 30 in Global Change Biology, found more than 725,000 acres — over 1,000 square miles — of damaged canopy from southern British Columbia to Roseburg. Researchers from Oregon State University and the U.S. Forest Service said the event caused an “unprecedented amount of foliage death,” triggering long-term stress that can slow growth, weaken trees’ disease resistance, and in some cases lead to mortality.
Hotspots for damage included timber farms and forested river basins near Florence and the Necanicum, Nehalem, Nestucca, Siletz, and Yaquina watersheds. Shade-tolerant trees such as western hemlock, Sitka spruce, and western red cedar suffered greater harm, while Douglas firs proved more resilient, especially at higher elevations.
Researchers also warned that current climate-change models may underestimate future forest vulnerability because they do not fully account for extreme events like the heat dome. The work was funded by the National Science Foundation, U.S. Geological Survey, and the Forest Service’s Pacific Northwest Research Station — a facility USDA plans to consolidate and move to Colorado.
Sources:
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Global Change Biology – (Peer-reviewed study)
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