The Washington state Department of Natural Resources (DNR) recently released its annual Forest Health Highlights report after joint aerial detection surveys flown by DNR and U.S. Department of Agriculture Forest Service staff over more than 20 million acres of forested acres across Washington, according to a news release from DNR.
Surveyors mapped approximately 545,000 acres of forests with some level of tree mortality, tree defoliation or disease in 2024 — an increase of nearly 30,000 acres from 2023 and more than the 10-year average of 519,000 acres, but well below the 672,000 acres mapped in 2022.
“The Forest Health Highlights DNR publishes each year makes the long list of things impacting our forests accessible and understandable to everyone from land managers to casual recreators,” Commissioner of Public Lands Dave Upthegrove said. “The report illustrates the importance of continuing to increase the pace and scale of not just forest health treatments but monitoring of forest health conditions.”
Outbreaks of the silver fir beetle in Washington are rare, but spikes in population sometimes occur following windthrow events that generate abundant breeding material, according to the release. Scientists mapped approximately 2,900 acres of beetle-caused mortality in 2024, the largest acreage documented since 6,400 acres were affected in 2004.
Recorded mortality caused by the beetle cratered in 2005 and remained low until 2015, reaching a peak of 1,700 acres in 2023 before falling again prior to 2024. It is possible that windthrow caused by 2024 weather events such as the bomb cyclone in November created additional beetle breeding material.
Areas with recorded silver fir beetle mortality in 2024 included North Cascades National Park in Whatcom County, the Snoqualmie Pass area in King County, and the Alpine Lakes Wilderness along the border between Chelan and Kittitas counties.
“Silver fir beetles may not be responsible for the largest or most damaging impacts we see on an annual basis, but they can be some of the most visible, given where they can occur,” DNR entomologist Glenn Kohler said. “We will certainly be interested to see if the current peak is sustained for a second year.”
Western spruce budworm defoliation in Washington surged to more than 63,500 acres mapped in 2024 following three years of no recorded defoliation attributed to the budworm. Outbreaks of this native insect are not uncommon in Washington, and this outbreak remains much smaller than an outbreak in 2011 and 2012 that affected more than 500,000 acres.
The current outbreak is most visible east of Ross Lake in Whatcom County, Skagit County and Okanogan County.
In addition to the prominent findings of the 2024 report, one of the most notable findings of the 2023 Forest Health Highlights, the arrival of California fivespined Ips beetle, in urban forest settings around the Puget Sound, remains an emerging concern.
Several locations from Bothell south to Tacoma experienced scattered pine mortality in 2023 and 2024 due to the beetle, which has now been detected in 14 Washington counties, extending its previously reported range from 1987 by approximately 150 miles to the north and 200 miles to the east, the release stated.
