Heightened tree mortality in Western Washington

Published 9:07 pm Saturday, June 15, 2013

Throughout Western Washington, the needles on many young Douglas-fir trees have suddenly turned red this spring, and the Washington State Department of Natural Resources (DNR) believes drought to be cause of the damage that is being observed.

DNR’s Forest Health Program has examined affected trees at several sites from Shelton, DuPont, and Auburn, south to Vancouver, and along the Columbia River Gorge. Douglas-firs that are between 5 and 15 years old appear to be the most commonly affected, but some larger trees are also showing symptoms including entirely red crowns, red tops, and red branches.

In a typical year, this type of damage may have many causes, but this year it is primarily the result of an extended period with little to no rain during August-September 2012 and a drier than normal spring in 2013. Damage has been most severe in areas with rocky soils, such as glacial outwash around the Puget Sound. Water drains quickly in these soils, and trees depend on occasional rains during the summer to replenish their water supply

The majority of trees that DNR’s Forest Health Program has examined show no indication of being killed by pathogens, insects, or other animals. Fortunately, even in the hardest-hit stands, the majority of trees received adequate water and are unaffected.

Landowners may see an increase in the number of red trees as the weather heats up, but if green trees have put out a flush of new, expanding bright needles on branch tips this spring, they are likely to survive.

For information, contact Glenn Kohler, DNR forest entomologist, 360-902-1342, glenn.kohler@dnr.wa.gov or your county WSU extension office.