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Recent western tree-kill by bark beetles has been the worst recorded

Native bark beetles are killing trees in millions of acres of western Native American forest.1 While in the US, historical records show periodic spikes populations,2 the extent and severity of beetle attacks occurring across much of the West since the 1990s has been unprecedented.3 Recent outbreaks have coincided with increased temperatures and changes in precipitation,4 suggesting a connection with the ongoing climate change in the region. One area that has suffered is eastern Washington State.

The most dramatic increases in mountain pine beetle populations have been in western Canada, where cold winter temperatures previously limited the insects’ spread and impact. With recent warmer temperatures, however, beetles have expanded their range in British Columbia, and the current epidemic is greater than any ever recorded in North America.5 The Canadian Forest Service predicts that if the current trends continue, 80% of mature lodgepole pines in British Columbia will die by 2013. Tree-kill at these massive spatial scales has shifted the carbon blaance of the forest from a sink to source. Authorities are also concerned that beetles will spread into Alberta and into Northern Canada’s boreal forest.6

References
  1. Western Forestry Leadership Coalition, "Western Bark Beetle Assessment: A Framework for Cooperative Forest Stewardship," (PDF) March 8, 2007.
  2. Raffa, Kenneth F., et al., “Cross-scale drivers of natural disturbances prone to anthropogenic amplification: the dynamics of bark beetle eruptions,” (PDF) Bioscience 58, no. 6 (2008): 501–517.
  3. Bentz, Barbara Western "US Bark Beetles and Climate Change" (United States Forest Service, May 20, 2008).
  4. Oneil, Elaine E. “Developing Stand Density Thresholds to address Mountain Pine 
Beetle Susceptibility in Eastern Washington Forests” (PDF) (University of Washington College of Forest Resources, 2006).
  5. Carroll, Allen L., et al., “Effects of climate change on range expansion by the mountain pine beetle in British Columbia,” (PDF) in Mountain pine beetle symposium: challenges and solutions, vol. 30, 2003, 223–232.
  6. Canadian Forest Service, “Mountain Pine Beetle Program Home,” September 1, 2009.