Researchers look into what's killing aspen
Rocky Mountain West trees dying, not reproducing
COLORADO STATE UNIVERSITY VIA THE ASSOCIATED PRESS
Tucson, Arizona | Published: 08.13.2006
DENVER — Something is killing the quaking aspen trees of the Rocky Mountain West.
The slender, white-barked trees that paint the hills gold every autumn are dying, some scientists say, leaving bald patches across the Rockies. Experts are scrambling to figure out what's happening.
"As soon as we understand what's going on, then maybe we can do something about it," said Dale Bartos, a Forest Service restoration ecologist based in northern Utah.
Bartos thinks a fungus may be to blame, while others suggest everything from hungry caterpillars to drought to man's interference with the natural cycle of forest fires — and even resurgent herds of hungry elk nibbling saplings to death.
Aspen stands have been hard hit in southwestern Colorado and Northern Arizona. Bartos said a conservative estimate is that about 10 percent of the aspen in Colorado may have died or become afflicted with something in the past five to 10 years.
Since 3.6 million acres across the state are classified as aspen-dominated, that 10 percent equals 360,000 acres, or 560 square miles, of dead or dying trees.
"We really don't know what's going on," Colorado State University forester Tom Wardle said. "We will, I'm very confident, figure it out."
More worrisome than the tree deaths is that aspen stands don't appear to be bouncing back from adversity the way they have in the past.
Aspen grow differently from other species. Rather than spreading through seeds, aspens send out shoots, called suckers, from giant, interconnected root systems. Each stand, or "clone" system, can live hundreds of years and some consider them the world's largest living things.
The trees themselves are just an aboveground manifestation of the communal root. A tree may die, but beneath the soil, the stand lives on, the root sends out fresh shoots, and the cycle begins again.
What has Wardle and others concerned is that stands with dying trees don't seem to have the vigor they normally have in sending out shoots to replace old trees — perhaps an indication that years of drought have inflicted deep damage.
In an 8,000-square-mile swath of Canada near Edmonton, Alberta, aspen is virtually the only species that grows in large numbers. Canadian Forest Service researcher Ted Hogg said as many as 30 percent of the aspen in the affected region may have been wiped out in the past five years; he suspects a combination of drought, heat, fungus and bugs.
Another Forest Service researcher, however, said there is no conclusive evidence of any long-term decline.
"We've taken a very long temporal perspective," said Claudia Regan, who works in suburban Lakewood. "We've looked at changes in forest conditions over several hundred years and examined if whether or not over that long time frame we see a decline in aspen. There really is no evidence of aspen decline."
Regan said it appears the number of aspen in Colorado has actually increased in the past century. It's noticeable when a clone dies off, she said, but reports seem to be isolated and anecdotal.
And if there is a decline, it might be a natural reaction to earlier human interference, University of Wyoming botany professor Dennis Knight wrote in a paper for the Forest Service back in 2001.
"Widespread disturbances caused by timber harvesting and fires in the late 1800s and early 1900s may have enabled aspen to become unusually abundant in the Rocky Mountains," he wrote.
"If aspen is now declining, the explanation may lie in natural processes. ... There is no basis to suggest that aspen is threatened globally, nor are most aspen groves likely to be lost in the near future."