The dead aspens around Collbran on Grand Mesa are representative of a larger trend of mature aspen stands dying in the West and even into Canada, researchers say.
Sudden Aspen Decline or SAD is responsible for the deaths of almost 10 percent of aspen groves in the San Juan National Forest. U.S. Forest Service officials say aspens in low elevations in the Grand Mesa, Uncompahgre and Gunnison National Forests are also dying at an alarming rate.
Severe drought earlier this decade weakened or stressed the trees, leaving them susceptible to disease, and insect infestations may be raising mortality rates, researchers say.
In trees affected by SAD, the roots are weakened, making it difficult for aspen stands to regenerate. Forest Service officials say that could eventually affect species that depend on aspens as well as economies that depend on hunting and tourism.
Forest pathologist Jim Worrall of the Forest Service said the trees dying today could have begun deteriorating three to five years ago. The trees first lose their green, heart-shaped leaves, the crown thins and branches die. A destructive canker or infestation and bugs could finish off the stressed trees.
Worrall said the die-off of aspens in the region is getting worse.
''It's actually not gradual at all as far as the trees are concerned. It's happened so fast, people are probably not aware of it. I feel like we can't get enough data to answer questions to provide information to the public," he said.
The Forest Service conducted an aerial study last year that showed the Dolores Ranger District in the state's southwest corner had 12,860 acres, or 9.84 percent, of dead aspen acreage.
The Grand Mesa National Forest experienced a loss of 4,552 acres, almost 4.5 percent of its total aspen acreage, according to the report. The study identified 138,000 acres of dead and dying aspen stands statewide.
The aspen die-off has generally moved from south to north, with reports first coming from Arizona years ago, Worrall said.
Areas in Colorado's northwest corner and into southern Wyoming, and areas in Canada, have reported a similar decline in aspen populations.
Aspen ecologist Dale Bartos of the Rocky Mountain Research Station in Fort Collins said he's seeing about 50 percent of aspens die off in areas in southern Utah.
''The trees are dying, and there isn't anything to do to stop that," Worrall said. ''We don't have any way to predict how far it could go."
Worrall and a team are studying the regeneration of aspens in the Dolores Ranger District to see how other stands can be saved. He said it was too early to draw any conclusions.