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Bark Beetles

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Beetle-killed trees on Mars Hill in Flagstaff. Click for larger image.

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Mountain pine (Ips) beetle and larvae (Dendroctonus ponderosae). Photo courtesy of University of Arizona Cooperative Extension Service. Click for larger image.

Aerial surveys conducted in the fall of 2002 show widespread ponderosa pine mortality from bark beetle infestation in the Southwestern region. Conservative estimates cite the loss of a half-million acres of forest. Some 60,000 acres are located in the Coconino National Forest and 7,000 acres in the Kaibab National Forest.

Bark beetles typically attack physiologically stressed trees. This stress can be caused by many factors including drought, lightning, mechanical disturbance, and fire. Trees in dense stands are stressed by having to compete for available moisture, light and soil nutrients. Overcrowded forest conditions coupled with drought has been the primary catalyst for the current epidemic of bark beetle infestation.

Very high levels of over-wintering bark beetles could lead to similar or even larger outbreaks in 2003. The Arizona Bark Beetle Task Force predicts that this year mortality will be at least as great as in 2002, or about 2 million trees killed, but the number could be much higher. If drought conditions persist, the epidemic could last for years; It can take several years of normal precipitation for stressed trees to rebuild carbohydrate stores used by the tree to produce beetle fighting resin (pitch).

The mortality from bark beetles increases the fire hazard by increasing accumulations of dead and down fuels. High fuel loading contributes to fire intensity, extreme fire behavior, fire persistence, resistance-to-control and burnout time.

For information on bark beetle control, click here.

References

The Bugwood Network. 2001. "Ips Species of the Western United States." http://www.barkbeetles.org/ips/Westips.html 4/17/03.

University of Arizona Cooperative Extension. 2003. "Ponderosa Pine Bark Beetles in the Prescott Area." http://ag.arizona.edu/yavapai/anr/fh/PrescottBarkBeetles.pdf 4/17/03.

University of Arizona Cooperative Extension. "Arizona Forest Health." http://ag.arizona.edu/extension/fh/ 4/17/03.

University of California Statewide Pest Management Program. 2000. "Bark Beetles - UC Pest Management Guidelines" http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7421.html 4/17/03.

U.S. Forest Service-Region 3. "Prescott National Forest News: Bark Beetle - Background Information." http://www.fs.fed.us/r3/prescott/health/health_beetles.htm 4/17/03.

J.G.

Last edited June 6, 2003

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