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Fir trees on Ajax are under attack

Jeremy Heiman

Editor’s note: This is the first in a series of two articles about a pair of organisms that are attacking trees, including the firs on Aspen Mountain. Part II will run Monday.

Subalpine fir trees on Aspen Mountain are under attack.

The attackers are tiny insects – the western balsam bark beetle – and its accomplice, a fungus called armillaria. Both the bug and the fungus are native to the spruce-fir forests that blanket much of the higher-elevation areas of the Colorado Rockies.

Scientific knowledge on the twosome is incomplete, but Forest Service officials say where one is found, the other is generally also present. They both attack mature trees, and often are found in trees that have been weakened by drought.

“On Aspen Mountain, it’s a problem,” said Jim Stark, winter sports administrator for the Forest Service’s Aspen Ranger District. Stark is coordinating a study being done by Forest Service entomologists in the Aspen area. The study area includes much of the Aspen Mountain ski area, though much of it is privately owned, because the beetle and the fungus have a foothold there, as well as on neighboring National Forest lands.

Study data shows that in 1995, 33 stands of fir on Aspen Mountain were affected by the organisms, though only a few trees in each stand were killed. Newer figures are not available, but Stark said the infestation on Aspen Mountain has picked up in the past year.

“If you look at the west side of Aspen Mountain, near the top,” Stark said, “that area’s really getting hit.” Larger areas of reddish-brown trees are visible there, and Stark said National Forest scientists think the infestation will continue to spread on that side.

“It may be getting to the point where we may have to start throwing money at it,” Stark said.

Keith Giezentanner, forest ecologist for the White River National Forest, however, said the balsam bark beetle and armillaria are not a cause for concern.

“Right now, the stuff that’s going on on Aspen Mountain is not considered a threat,” Giezentanner said. “We’re going to continue to lose trees. It’s a natural situation.”

Jonathan Lowsky, wildlife biologist for Pitkin County, goes one step further, maintaining that organisms such as armillaria and the beetle are actually beneficial.

“Natural disturbances such as rockfall, landslides, wind, insects and disease promote forest-type diversity and age diversity,” Lowsky said.

A 50-acre stand of fir trees killed by insects may be replaced by lodgepole pine or aspen, he said, increasing species diversity. The standing dead trees create habitat for cavity-nesting birds, as woodpeckers drill them to find insects.

“Our problem as humans is we are very short-sighted,” Lowsky said. “You need to think in terms of hundreds of years, when you’re talking about ecology on a landscape scale.”

Insects and disease fit into a ecological concept called the “shifting steady-state mosaic,” Lowsky said. It states that, if disturbances are allowed to continue, there will always be a similar variety of tree species and ages, though they will exist at different places on the landscape at different times.

Nonetheless, said Forest Service ecologist Giezentanner, dead trees present an aesthetic question on a popular ski area.

“When you’re talking about something like a ski area that markets scenery, it can be a problem,” he said.

Stark said the Aspen Skiing Co. has been cutting the firs as they die on Aspen Mountain, for just those aesthetic reasons. But to really affect the spread of the disease, he said, all the trees within about 30 feet of each dead tree would have to be cut, because by the time one tree dies, the beetles have spread to all the others within that 30-foot radius.


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