Global warming blamed for aspen die-off across the West

Nicholas Riccardi in the Los Angeles Times: 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.

…The most vulnerable trees grow on sunny, south-facing lower elevations, where warmer temperatures wear down the trees' resistance to pests. And though the largest number of deaths is in Colorado -- which has the most aspens -- the effect can be even more severe in places like Nevada, Arizona or California that have small bands of aspen….

An aspen tree in Jasper National Park, Alberta, Canada, shot by Fairsing, Wikimedia Commons