For background information and additional context, see our Tree Mortality and Fire page.
Bark beetles are important disturbance agents that can cause extensive tree mortality in western forests, often affecting larger areas than fire (Raffa et al., 2008). Bark beetles are attracted to trees that are stressed or weakened from pathogens and abiotic factors like drought, fire, and smog. Thousands of acres of California forests in the Sierra Nevada, especially in the southern Sierra, have been decimated by outbreak bark beetle populations and “U.S. Forest Service scientists say more than 12 million trees in the state’s forests have perished during the drought, and the die-off is expected to continue” (Los Angeles Times, May 6, 2015).
In the north coast where conditions typically are wetter and milder, extensive mortality from bark beetles is uncommon, especially in coastal forests where pathogens and other secondary insects can play a more prominent role in tree mortality. However, with changing climates, extended drought, and increased incidence of high severity wildfire, future bark beetle populations have the potential to increase, thereby increasing tree mortality.
For more information:
Bark beetle natural history and ecology
Raffa, K.F., Grégoire, J-C. & Lindgren, B.S. (2015) Natural history and ecology of bark beetles. In: Vega, F.E. & Hofstetter, R.W. (Eds.), Bark Beetles. Biology and Ecology of Native and Invasive Species. Academic Press, London, pp. 1–40. Natural History and Ecology of Bark Beetles
Climate change and bark beetles
Bentz, Barbara J.; Regniere, Jacques; Fettig, Christopher J.; Hansen, E. Matthew; Hayes, Jane L.; Hicke, Jeffrey A.; Kelsey, Rick G.; Negron, Jose F.; Seybold, Steven J. 2010. Climate change and bark beetles of the western United States and Canada: Direct and indirect effects. BioScience. 60(8): 602-613. http://bioscience.oxfordjournals.org/content/60/8/602.full
Bark beetles and fire in western forests
Bark Beetles and Fire: Two Forces of Nature Transforming Western Forests. Fire Science Digest. ISSUE 12. FEBRUARY 2012.https://www.firescience.gov/Digest/FSdigest12.pdf