Bark beetle infestation decimates Colorado
ASPEN ” A bark beetle infestation that has already ravaged forests in parts of Colorado grew at an “unprecedented” rate in 2007 and affected 500,000 additional acres, the U.S. Forest Service reported Monday.
The growth of the beetle epidemic affecting lodgepole pine forests last year was “unprecedented,” said Rocky Mountain Regional Forester Rick Cables. The infestation has hit about 1.5 million acres in the state since the first outbreak in 1996, according to an aerial survey conducted last summer.
All mature lodgepole pine forests will be dead in Colorado within three to five years, said Susan Gray, a group leader for forest health management in the Rocky Mountain Region. “We’ll lose all the older, larger trees,” she said.
The infestation kills entire hillsides of lodgepole pine trees and leaves behind rust-colored skeletons. The impacts are as simple as eliminating natural breaks that trees provide between campsites in national forests and causing an aesthetic blight for sightseers. Impacts could be as severe as eliminating cover that allows slopes to hold snow and allowing erosion that clouds water quality, officials said.
The infestation mainly was isolated to five counties in northern Colorado but spread to some Front Range areas last year, the Forest Service survey determined.
Pitkin County largely has been spared from the wrath of the mountain pine beetle. Maps showing the new infestation in 2007 show pockets of outbreaks just outside Aspen and northeast of Ruedi Reservoir.
The Forest Service estimated that 1,200 acres of lodgepole pine forests in Pitkin County were infested in 2007, said Bob Cain, an entomologist with the agency’s regional office. That’s a significant level, but not close to the devastation that areas such as Vail, Summit County and the Winter Park area have experienced.
Cain said the intensity of detection in Pitkin County averages about three trees per acre. In contrast, it’s 50 trees per acre near Granby, where entire hillsides died off.
Jan Burke, a silviculturist with the White River National Forest supervisor’s office in Glenwood Springs, said the low level of mountain pine beetle infestation in the Roaring Fork Valley is a product of forest composition.
The Aspen-Sopris Ranger District has about 54,000 acres of lodgepole pine or stands that include those trees, she said. About 55 percent of those trees are of the age and size that are most susceptible to the mountain pine beetle. That means 29,000 to 30,000 acres surrounding Aspen, Basalt and Carbondale are susceptible, Burke said.
Although the mountain pine beetle infestation and its potential are limited in the Aspen area, other forest health issues loom, experts warned.
The Forest Service estimated that about 15,000 acres of aspen trees died in Pitkin County last year. The agency has several projects under way statewide to learn more about what it calls Sudden Aspen Decline.
Spruce stands, which are more prevalent in the high country around the Roaring Fork Valley, also are under attack from a specific beetle that targets only them.
“The spruce beetle infestation, I’m just holding my breath,” said Burke.
The regional office estimated that about 1,100 acres of spruce forests were affected by beetles in 2007. Burke said that figure is “grossly underestimated.”
“It’s incredibly difficult to detect spruce beetle from the air,” she said.
Tom Eager, a Forest Service entomologist who works in the White River National Forest, said the spruce beetle epidemic could have an even greater effect on Colorado in the long run their the mountain pine beetle infestation. There are more acres of spruce forest and it takes a longer time for them to regenerate, he said.
Spruce beetles are on a two-year life cycle, with the adults breeding and laying eggs every other year rather than annually, like mountain pine beetles. Therefore, a spruce beetle infestation takes longer to develop. But Eager and Burke said there are signs it is spreading. How long before there is infestation is difficult to say. Drought and warm winters speed infestation.
“You tell me what the weather’s going to do, I’ll tell you what the beetles are going to do,” Eager said.
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