Beetles are on the move in Aspen-area forests
Aerial survey shows slow, steady spread of Douglas fir beetles in Roaring Fork Valley
The Roaring Fork Valley experienced a spread of Douglas fir, spruce and western balsam bark beetles last year but the infestations remained light compared to many other parts of the state, according to the latest assessment.
The U.S. Forest Service and Colorado State Forest Service released results of their 2020 Forest Insect and Disease aerial survey this week. The annual flyover of the state’s forests was pared down last year because of COVID-19 challenges. It covered 16 million acres or about half of prior years. The Roaring Fork Valley was one of the priority areas.
“I can share (that the) spruce beetle has moved into the Aspen area, particularly in the northern reaches of the Elk Mountains,” Dan West, forest entomologist with the state forest service, wrote in an email.
The aerial survey indicated the White River National Forest had about 160 acres of new spruce beetle activity that was detectable from the air. The infestation is likely more widespread, he said, because what can be seen from the air is usually less than what’s occurring on the ground.
The survey also determined that the Douglas-fir beetle infestation has intensified because of the Lake Christine Fire of July 2018 on Basalt Mountain.
“Moderately scorched trees are havens for bark beetles, and the trees along the burn perimeter were likely brood trees for these beetles,” West said.
Forest health assessments are vital because Colorado’s forests have come under pressure from climate change. Warmer temperatures and unpredictable precipitation levels are stressing trees, said Adam McCurdy, forest and climate director at Aspen Center for Environmental Studies.
He said Douglas-fir beetles have been a slow but growing problem primarily downvalley from Aspen, with spot infestations in Castle Creek Valley, the ridges north and east of Snowmass Canyon and the Fryingpan Valley.
“To me, that’s a big and continuing part of the forest health story,” McCurdy said. “I don’t think it’s gotten enough attention in the valley.”
The Douglas-fir beetle problem has been a “slow burn” compared to the mountain pine bark beetle infestation that was so visible in many parts of the state, he said. Large swaths of lodgepole pine trees in the Interstate 70 corridor died and turned rust color during the pine beetle infestation of the late-1990s and early-2000s. The Roaring Fork Valley was largely spared from the mountain pine beetle infestation because of diversity in tree types and age classes.
The aerial survey report includes a map that shows areas of infestation from various beetles. The terrain surrounding the Roaring Fork Valley has what looks like small freckles representing the outbreaks. Other parts of the state are covered with larger blotches representing more widespread infestations.
McCurdy said Douglas fir trees have proven in the past to be resilient because they are hardier in a warmer climate. Recent droughts and warm temperatures have stressed them.
West agreed that drought in the Roaring Fork Valley and throughout Colorado has made Douglas firs more vulnerable to beetles. Last year’s weather pattern added to the problem.
“Plenty of snow during the winter, then dried all up and severe to extreme drought conditions cause trees to become vulnerable,” West said. “I don’t think 2021 will be any different, since the drought continues through much of the central and southern mountains.”
McCurdy pointed out that intense Douglas-fir beetle infestations are on the doorstep of Pitkin County, in eastern Gunnison County.
In addition to Douglas-fir infestations, the aerial survey map shows small outbreaks of western balsam bark beetles in higher elevations of the Independence Pass corridor as well as Castle and Maroon creek valleys. Sub-alpine fir trees are vulnerable to the western balsam bark beetles. There are also a few small pockets of spruce beetle infestations in the Roaring Fork watershed.
White River National Forest officials were concerned about a potential spruce beetle outbreak after a landmark avalanche cycle in March 2019. The slides wiped out untold acres of mature spruce and other trees in areas such as Conundrum Creek Valley and Lincoln Creek Valley.
West said there is limited potential for the debris piles to host an infestation.
“The slide areas and debris fields containing Engelmann spruce are sources of viable food for the spruce beetle, but really only for one season, maybe two at most if the piled material is deep and sun really cannot penetrate to the wood buried down in the pile and dry it out,” West said.
The Colorado State Forest Service also identified disease in Colorado’s signature aspen trees as another emerging problem in 2020, largely because of drought.
The White River National Forest’s aspen management plan will include timber harvesting and prescribed burns in the Aspen-Sopris Ranger District. To learn more about the project, go to https://www.fs.usda.gov/project/?project=59419
The project web page includes a section on submitting comments. The comments need to be received on or before April 20.
McCurdy said there is ample evidence of aspen stands experiencing problems in the Aspen area: the Cemetery Lane side of Sunnyside Trail, upper Buttermilk and the west side of Castle Creek Valley downvalley from Toklat Lodge among them.
The White River National Forest announced Thursday a major proposal for a decades-long aspen management plan. The 2.3-million-acre forest contains an estimated 600,000 acres of aspen trees. About 375,000 acres are targeted for timber harvesting and prescribed fire to maintain and expand aspen stands.
“Within this 375,000-acre area, the Forest is proposing to use various harvesting methods on up to 10,000 acres per decade in combination with an additional 10,000 acres per decade of prescribed fire,” the forest supervisor’s office said in a news release.
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