Aspen’s signature trees facing threat

Sudden aspen decline devastating the eponymous tree

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By Charles Agar
Aspen Correspodnent
March 26, 2008

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ASPEN — What would Aspen be without its signature tree?

A statewide phenomenon is killing off massive swaths of aspen trees, some 54,000 acres of aspens alone in the White River National Forest in and around Pitkin County.

U.S. Forest Service officials studying the problem went before the Pitkin Board of County Commissioners at a work session Tuesday.

“We’re not talking the end of aspens here,” said Roy Mask, an entomologist with the U.S. Forest Service. But in recent years, scientists have witnessed “significant mortality rates.”

The die-off of aspens affects vast tracts on a “landscape” scale, Mask said, and onset of the problem is swift and devastating.

In 2006, 140,000 acres of aspens died off statewide, and in 2007 the number skyrocketed to 338,000 acres, with many new areas of aspen-kill on the Western Slope, Mask said.

Stands of aspens share a common root system, and groves at lower elevations or facing the warm western or southerly direction are increasingly affected.

Scientists originally were baffled by the phenomenon but are learning more in ongoing studies.

The dieback normally is accompanied by bark beetles, wood-boring beetles and a kind cytospora canker, Mask said, adding that the various pathogens don’t necessarily kill the tree but are common to affected stands.

Mortality is higher in older aspen stands that are more open and spread out, Mask said.

Scientists believe the phenomenon is the result of drought conditions in recent years.

Dying stands of Aspens can regenerate as long as root systems still are healthy, Mask said, but regeneration requires a “sprouting trigger,” commonly a major disturbance such as a forest fire.

Clear-cutting dying stands of trees has proved effective in some areas, according to Mask.

Forest Service officials are monitoring sites closely around the state.

Irene Davidson, the district ranger with the U.S. Forest Service, said there is nothing to do in the immediate future for threatened aspen trees locally, but state and federal officials are closely watching the problem.