Beetles advance in national forest
ASPEN – Hikers, mountain bikers and other forest visitors better get used to the brown color of dead trees. They might see a lot of it over the next decade.The White River National Forest is facing a spruce beetle epidemic that threatens to wipe out thousands of Englemann spruce and subalpine fir trees over hundreds of thousands of acres in the next 10 years, according to experts with the U.S. Forest Service.The outbreak has already turned stands of trees brown on mountainsides just west of Vail. The Aspen area is largely untouched, but probably not for long, according to Tom Eager, an entomologist who is helping assess the bark beetle risk in six national forests in Colorado and surrounding states.”The White River National Forest is probably one of our bigger concerns,” he said.
That’s because the spruce and fir trees have reached what’s considered a mature and overmature age of 100 to 125 years. Spruce beetles target older trees because their defenses aren’t as strong, Eager said. And the beetles are particularly vicious during times of drought like Colorado is currently suffering, he said.Spruce and fir trees produce resin when attacked to try to “pitch out” the beetles from the holes they bore. The amount of resin they are able to produce depends on moisture levels, Eager explained. So in times of drought, stressed trees don’t have as great a defense.The spruce beetle is a native insect that’s always present in the forest, according to Forest Service materials. But it takes the right conditions to produce an epidemic.Aging trees and drought aren’t enough to produce an outbreak, though. There also needs to be a “triggering event,” Eager said.That event happened in the Roaring Fork drainage in Aug. 18, 1999, when hurricane-force winds ravaged spruce, fir and aspen trees on about 3,000 acres in the Baylor Park, an area in extreme western Pitkin County roughly 13 miles southwest of Glenwood Springs’ Sunlight Mountain Resort ski area.
The area looks like a giant went through and scattered thousands of trees and snapped off thousands of others about 15 feet off the ground.”This was the perfect storm for spruce beetles, providing the ideal breeding condition,” according to the White River National Forest’s 2003 annual report.The beetles lay their eggs beneath the bark of the defenseless trees. Their numbers then increase to the point where they start attacking the surrounding live trees.The Forest Service estimates that 3,000 large spruce trees were killed on 2,800 acres across the forest. The potential to spread is tremendous: “The Forest has 100,000 acres of large spruce stands that are at high risk of mortality in the next 10 years from this emerging beetle epidemic,” the annual report said. “Spruce trees are also at risk on an additional 500,000 acres where they comprise part of the stands.”Eager avoids making predictions about how severe the problem will be. If you could tell him what the weather is going to do over the next few years, he could make a reasonable estimate about the epidemic.
Continued drought will spark an infestation over the next decade. Wet weather will delay but not end the threat, he said.When beetles target a specific stand of spruce or fir, it can wipe out “95 percent-plus” of the trees in that area, Eager said.Since spruce beetles are native to the area, there is debate within the forest service on how much activity it should undertake to slow the spread of the beetles.”It’s really a societal thing,” said Bill Westbrook, the Aspen and Sopris district ranger. “Do we want to see vast acreages of brown trees?”It will require Mother Nature’s help to break the infestation. Sustained winter temperatures below -35 degrees or extreme, quick freezes in spring or fall can kill off large numbers of the pests, Eager said.Scott Condon is a writer based in Aspen. He can be reached at scondon@CMNM.org.Vail Colorado