In lodgepole pine forests, resident bark beetles help regulate the population. Epidemics fuel the fires that regenerate overgrown, aging forests.

But now the beetles are on the march, moving higher up mountain ranges and further north, where their reproduction rates have reached unprecedented epidemic proportions. From Bryce Canyon National Park in southern Utah to the Brooks Range in Alaska, once robust pine forests have turned rusty orange. Lodgepoles and ponderosas are dying in numbers not seen in centuries, and pinon are vanishing as the keystone species throughout much of the Southwest.

Urban sprawl and industrial agriculture have accounted for much of the deforestation in the American West. But with the warming of the climate, bark beetles have also encroached - in 2004 alone, 8.5 million acres in 12 western states infected.

Exotic bugs introduced by European settlers, drought and federal fire suppression policies have all conspired to make our forests more susceptible to insects. But a computer model created by USU applied mathematician James Powell and U.S. Forest Service entomologists Barbara Bentz and Jesse Logan implicates global climate change as well. In a complex mathematical analysis of forest service field data, the model demonstrates changes in beetle behavior that can only be explained by rising temperatures. The cold-blooded beetles reproduce more quickly, especially in climates that used to be inhospitable, because of the accelerated aging induced by warmer winters.

The most defenseless trees are the long-lived white bark pines found at high elevations throughout the northern Rockies. "Perhaps no other tree embodies our sense of the American West to quite the extent of a gnarled, 1,500-year-old white bark pine clinging to life under some of the harshest conditions on the continent," Powell and Logan wrote in the introduction to their federally and state-funded computer model. more