Earth Notes
4:14 pm
Wed September 29, 2010

Earth Notes - Aspens Part I

Flagstaff, AZ –
Aspens are among the West's signature trees. Their heart-shaped leaves rustle in the slightest breeze, filling the forest with a gentle shhhushing sound. In autumn, those leaves form a golden contrast with the dark green of high-elevation conifers.

Aspen groves are resilient. They send up new trees when they're singed by fire, withered by drought, or attacked by insects. But lately, something's changing. Biologists began to notice in 2004 that aspen groves all over the west were dying at unprecedented rates.

Surveys in Arizona's Coconino, Apache-Sitgreaves, and Kaibab national forests have showed that 90 percent of aspens at low elevations have disappeared, with older trees most at risk. More than half a million acres of aspens have been damaged in Colorado, as well as groves in Wyoming and Utah.

Scientists have dubbed the phenomenon Sudden Aspen Decline, which they abbreviate with the acronym SAD. They believe that the drought from 2000 to 2005 was the trigger. It weakened vulnerable stands and made them more susceptible to threats they'd normally resist, like browsing by elk, and attacks by aspen bark beetles.

When a grove starts to decline, competition can be the final straw, as other tree species move in to fill the void.

Biologists are looking toward long-term solutions to stem the tide, including slowing encroaching conifers and reintroducing fire. Meanwhile, they're actively promoting shorter-term fixes, like fencing, to give regenerating aspens half a chance to survive. You'll hear more about that next week.

-Anne Minard