Bark Beetles Account for More Than Half of Tree Mortality Reported in Annual Forest Health Highlights
News Date: 
April 25, 2023

DNR and Forest Service scientists report a 10-year high of forested acres affected by tree mortality, defoliation, or foliar diseases

The Department of Natural Resources released its annual Forest Health Highlights report on Tuesday following a 2022 survey that returned to normal operations for the first time since the start of the COVID-19 pandemic.
Surveyors from the Department of Natural Resources (DNR) and U.S. Forest Service flew over approximately 22 million forested acres across Washington for the annual insect and disease aerial detection survey. The 2021 report covered 19 million acres; crews did not fly in 2020 due to the pandemic for the first time since 1947.
The report details the 672,000 acres observed to have some level of tree mortality, defoliation, or foliar disease – a 14,000-acre increase from the last full-scale survey in 2019. Bark beetles accounted for 346,000 of the 604,000 acres with damage from mortality agents.
“This report makes clear that western Washington continues to face increasing threats to forest health and greater risk of severe wildfires,” said Commissioner of Public Lands Hilary Franz. “We’ve made great progress on our 20-Year Forest Health Strategic Plan for eastern Washington. Thanks to investments from my Cascading Impacts of Wildfire legislation passed this session, and expansion of our Wildfire Ready Neighbors program, we will start addressing the needs of our forests west of the Cascades.”
The marked increase in mortality caused by bark beetles was not limited to just one species, or one specific region of the Evergreen State.
Scientists reported tree mortality caused by Douglas-fir beetles across 105,000 forested acres in 2022, the highest level recorded since 2001 and more than double the 10-year average. They also mapped mortality of ponderosa pine due to western pine beetle at a 16-year high of 44,300 acres. Pine bark beetle-caused mortality increased from 2021 totals in all pine host species.
Areas that saw the highest concentrations of bark beetle-caused mortality included wide swaths of Yakima County, Kittitas County, and Okanogan County. Most of the increase of Douglas-fir beetle-caused mortality occurred in those three counties, as well as in the Blue Mountains southeast of Walla Walla.
Much of the Puget Sound region, including King County, Pierce County, and Lewis County, saw higher concentrations of Douglas-fir beetle-caused mortality compared to the rest of western Washington.
“Recent drought conditions and extreme heat events like the 2021 heat dome are likely driving up bark beetle activity in some areas of western Washington,” said DNR entomologist Glenn Kohler.
Despite a wet spring, prolonged hot, dry periods stretching from summer into fall resulted in all of Washington being in at least moderate drought conditions by late October, according to the U.S. Drought Monitor. Prolonged droughts are one of the major drivers of increased tree stress and insect outbreaks in Washington.
Following the record-setting heat and drought conditions of the previous year, scientists observed continued spread of sooty bark disease throughout Washington. Caused by a fungus that until recently was thought to be contained to the greater Seattle area, sooty bark disease has now been found as far east as Pullman, south into Oregon, and north of Bellingham. This pattern is in line with European studies that show increased rates of sooty bark disease spread following hot, dry summers.
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