CSI Colorado: Sudden Aspen Decline Post-Mortem

Droughts kill trees — but until now scientists didn’t know the root of the problem

Aspens live at high elevations in the Western United States, including in California's White Mountains and Sierra Nevada.

Throughout the West, aspens are quaking for good reason.

About 17% of the aspen in the Colorado Rockies have died in the last decade. That’s about one in every six trees. The widespread die-off, called sudden aspen decline, began after a severe drought and heat wave. So people studying the trees knew that’s what triggered the deaths, but they didn’t know what exactly killed the trees.

William Anderegg, a grad student at Stanford, with help from a team of scientists there and at the University of Utah, has zeroed in on the culprit, and describes the work in a paper published this week. There were two working theories: failures in photosynthesis, which would mean less food for the tree; or damage to the roots, which would mean less water. Anderegg found it was the roots.

“Our study provides a snapshot of what future droughts could hold for the emblematic tree of the American West,” Anderegg said in a press release. “Our results indicate an impaired ability to transport water due to drought damage plays an important role in the recent die-off of aspens,” .

With this research, scientists will be able to better understand and predict how forests will respond to rising temperatures and drier conditions.