The trees, which were already under duress, are being killed by insects that thrive as the climate changes. Scientists call it Sudden Aspen Decline. Dying aspen trees. Aspens are a big fall tourist draw, but this year there's less color. The trees had already been under duress before what foresters term Sudden Aspen Decline struck. (RJ Sangosti / The Denver Post)

By Nicholas Riccardi, October 18, 2009 Reporting from Paonia, Colo. –  From the hillsides of extinct volcanoes in Arizona to the jagged peaks of Idaho, aspen trees are falling by the tens of thousands, the latest example of how climate change is dramatically altering the American West. Starting seven years ago, foresters noticed massive aspen die-offs caused by parasitical insects, one of them so rare it is hardly even written about in scientific literature. But with warming temperatures and the effects of a brutal drought still lingering, the parasites are flourishing at the expense of the tree, beloved for its slender branches and heart-shaped leaves that turn a brilliant yellow in autumn. What foresters have termed Sudden Aspen Decline affects more than just aesthetics. Aspen trees provide a rich habitat for birds, elk, deer and other animals. The grasses that sprout under them — up to 2,000 pounds per acre — hold water that is needed by metropolitan areas. The trees do not burn easily and create natural firebreaks in forests already ravaged by the pine bark beetle — another parasite that is thriving because of global warming. “It’s just rolling through the forests,” Wayne Shepperd, an aspen specialist at Colorado State University, said of SAD. Noting the number of other changes to Western vegetation due to warmer, drier temperatures, he added: “Everything’s happening all at once. We’re living in interesting times here.” The decline of the tree is most visible in Colorado, which has seen nearly 500,000 acres afflicted by SAD — nearly a fifth of its aspen groves. …

Global warming blamed for aspen die-off across the West via The Oil Drum