Bark Beetles are attacking drought-stressed trees


Washington residents have reported uncharacteristically high numbers of dead and dying Douglas-fir trees to the Washington State Department of Natural Resources this spring and summer. The culprits: drought and bark beetles.

The native bark beetle species involved are opportunists, also known as secondary bark beetles. They don’t normally have the capacity to kill live, healthy trees. Instead, they breed in dead or downed branches and then infest small diameter, thin-barked portions of trees that are stressed or dying from factors such as root rot, fire, or drought.

A doubling of public inquiries tipped off DNR scientists whose field observations have confirmed the public’s forest concerns. Those driving highways in South Puget Sound and lowlands around Blewett, Sherman, or White passes will likely spot the damage to Douglas-fir trees.

“Bark beetle infestation is a visible manifestation of drought conditions, stressed trees, and unhealthy forestland,” said Commissioner of Public Lands Hilary Franz. “Unfortunately, this infestation increases the risk wildfires in the forests that surround our communities. If you own forests or trees, do your part to make sure they are healthy so they survive and continue providing ecological benefits for you, your neighbors, and our state.”

Washington has had several years in a row of hot, dry summer weather. Douglas-fir trees in particular have been heavily affected by these drought conditions, which showed similar — though less significant — signs of stress in 2012 and 2015. Some trees seem to be dying from drought alone. It’s this stress and easy access into the trees that has allowed beetle populations to grow larger than seen in recent years.

The primary symptoms of bark beetles are entirely red crowns in saplings, and red tops or scattered branches of red needles in larger trees. The damage is commonly visible in scattered areas throughout eastern Washington and in western Washington in dry lowland areas and sites with well-drained soils.

DNR is currently flying aerial surveys across the state to assess the breadth of damaged trees. These annual flights help the agency better understand the extent of infestation and other forest health issues. Results will be available by November.

Franz’s 20-Year Forest Health Plan for eastern Washington includes strategies to help improve the health of our forests and decrease such outbreaks, leaving more productive forests that can better withstand wildfires. Adopted last fall, the plan calls for treating 1.25 million acres of forest by 2037.

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