Mysterious decline of aspens concerns foresters (CO)

The Denver Channel
July 13, 2006

Up to 60 percent of aspen stands in the Dolores Ranger District's Turkey Knolls area are dead or dying, and that's raised more than a few eyebrows among forest officials and local business leaders.

"I think we're going to see huge changes in 30 to 40 years," said Phil Kemp, forester with the Dolores Public Lands Center. Turkey Knolls is about 12 miles north of Mancos.

Kemp first noticed the change in aspen stands two to three years ago, but the first official report of dying aspens in Southwest Colorado came when the U.S. Forest Service's forest health management group did an aerial survey of the area, marking the changes in aspen stands.

Dying aspens have been recorded in other states as well, but there is no apparent pattern, said Wayne Shepperd, research forester with the Forest Service's Rocky Mountain Research Station in Fort Collins. "It seems to be occurring at different places and to various degrees," he said.

"We have lots of questions, but no answers," Shepperd said. "We haven't seen anything like this in Colorado before."

The Durango and Bayfield areas have not seen widespread aspen death, according to Dave Crawford, a forester with the Bayfield-based Columbine Ranger District. A stand of aspen trees near Electra Lake along U.S. Highway 550 "gives the appearance that it's dying off," but has begun to recover and re-leaf despite the presence of defoliating tent caterpillars, Crawford said.

The Bayfield silviculturist speculated the relative health of La Plata County's aspens may be due to more spruce trees standing among the aspens and generally higher elevation. But he added that the area's long, unusually hot drought could produce unforeseen consequences.

Kemp and the team of researchers have not been able to determine why the aspen stands are dying or why the mortality may be occurring at this point, but they suspect repeated years of drought, as well as insects and disease, may play a role. Without the needed moisture, aspens are weaker and less resistant to insects and disease.

Although aspens have a relatively short life cycle that typically spans about 100 to 150 years, very little regeneration has occurred in the Turkey Knolls area. According to Jim Worrall, forest pathologist for the Forest Service's Rocky Mountain region, European settlement sparked the growth of most aspen stands and now those stands have reached maturity simultaneously. This might contribute to the widespread epidemic.

To further complicate the problem, aspens are widely considered to be one of the largest living organisms, if not the largest living organism, because the roots in an aspen stand are all connected. This clone of aspens usually means other trees will sprout from the shared root. But when Kemp and his crew did some root trenching, they dug up no live roots.

"It was sobering," Shepperd said. "In some places, this means aspen is going to die and won't be back."

These stands of mature aspen may have 400 to 600 stems per acre, with a stand of aspen clones covering tens to hundreds of acres, according to Shepperd. Aspen is king in Colorado, he said, but the San Juan National Forest is particularly unique in that it is the pinnacle of aspen growth in the state.

The loss of the area's aspen trees would be visually disappointing during future fall foliage seasons. The economic and ecological impacts would be far greater.

About 20 percent to 30 percent of the Cortez area's fall visitors are here to look at foliage, said Kelly Allmon, director of the Cortez Retail Enhancement Association.

That is not the only economic driver for aspen trees.

"More so in the Cortez-Mancos area, it has economic value because in Southwest Colorado there are businesses specifically oriented toward aspens," Worrall said.

Two local logging mills rely on aspens for business.

The problem of overmature aspens also affects biological diversity, since aspens have more species associated with them than many other trees in the area, Worrall said. Bird cavities tend to be more common in aspen stands. Deer and elk feed on aspen roots. Additionally, herbaceous plants and wildflowers grow in the stands.

While the team of foresters and researchers has not determined why so many aspens are dying, Kemp said the only solutions at this time are fire and clear-cutting.

Aspens are considered somewhat fire resilient in that they are one of the first species to reinvade a fire site.

"It thrives on abuse," said Shepperd. "It's a masochistic species, I guess."

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