Picture of Martyn Overy
Beetles+Dought= Bad news for Arizona's Forests
by Martyn Overy - Saturday, 5 July 2003, 11:58 AM
 


The drought and high winds, experienced by Arizona's forests, is providing ideal conditions for devastation by fire. This is bad enough, but this year the devastation is being amplified by a small creature which is actually creating a far greater degree of damage to trees. In 2002, the bark beetle were responsible for killing more trees in Arizona than the total number of wildfires. There are now poised to destroy over 1 million acres of prime forest.

This epidemic is the largest that scientists have seen. The scale of devastation is wide and extensive, with an estimation of over 800,000 acres of land having been infested.

The drought has allowed the bark beetles to have an exceptionally successful breeding season. They then burrow into trees and lay eggs. The inner bark provides a food source. This process has the result of destroying or clogging the tissues that allow water from the roots to move up to the branches.

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A spruce beetle ( University of Arizona )

In 'normal' seasons, the resin produced by the trees would provide a defence barrier against such attacks, but the severe drought has resulted in a greatly reduced defence mechanism against attacks from insects.

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Images showing the devastation by the bark beetle ( University of Arizona )

This has resulted in the death of over 6 million trees. In 2001 the extent of the damage was 50, 000 infested trees, so in the space of two years the extent of the damage has increased by a factor of 16 . There appears to be worse to come, since the population of beetles is still increasing, with the next generation about to arrive within the next few weeks.

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Adult and eggs

Photographer: Edward H. Holsten, USDA Forest Service.

By killing the trees, the beetles have provided new sources of firewood for this drought-striken season. A particular risk is dead trees from the infestation falling onto power lines, and the resulting sparks and charges providing the ignition for further forest fires. The high density of trees has also reduced the distribution of water to each tree, and increases the risk of attack by infestation and fire.

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USDA Forest Service - Rocky Mountain Region Archives, USDA Forest Service

Descriptor: Adult

Description: callow adult

Arizona is not alone with this severe attacks on trees by these beetles. Outbreaks have also been reported in New Mexico, Colorado, and Southern California.

Further reading :
The Pine Beetle Outbreak in Arizona

TheArizona Forest Health

Bark beetle factsheet