Tree-kill by bark beetles has recently spiked in Washington State

In eastern Washington, there were 20 times more trees killed from 2000 to 2004 than in the prior 20 years combined.[[Oneil, Elaine, Bruce Lippke, and Larry Mason, “Discussion Paper (DP8): Eastside Climate Change, Forest Health, Fire and Carbon Accounting,” (PDF) July 2007.]] The US Forest Service has created an online animation that shows the increase in tree mortality across the Pacific Northwest since 1980.[[United States Forest Service, “Animated Map: Mountain Pine Beetle in WA,” February 10, 2009.]] This trend is consistent with a broader pattern of beetle kill in the West that appears related to climate change.

Elaine O’Neil’s research at the University of Washington has found that beetle outbreaks in Eastern Washington were predicted by high heat and low moisture — weather conditions in which pine trees need to shut down to conserve water. In this stressed state, she found the trees were extremely vulnerable to attack.[[Oneil E.E “Developing stand density thresholds to address mountain pine beetle susceptibility in eastern Washington forests.” (PDF) PhD Dissertation, University of Washington, Seattle, 99pp. (2006)]] Projections for mountain pine beetles in Washington State indicate that while beetles will impact more trees at higher elevations due to warming, impacts at lower elevations may decrease because conditions will become too hot and dry for the beetles.[[Littell, Jeremy S., et al., Forest Ecosystems, Disturbances, and Climatic Change 
in Washington State, USA (PDF) (Climate Impacts Group), 2009.]]