Observers who are noticing dying conifer trees around the Roaring Fork River watershed can blame the Douglas-fir beetle.
The valley has avoided many of the insect infestations that have decimated parts of Colorado over the past two decades, but two pests targeting fir trees have made their mark, according to an annual aerial survey performed by the Colorado State Forest Service and U.S. Forest Service. Results were released Monday.
The agencies’ report featured an interactive map that shows what pests are affecting which areas of the state. The Douglas-fir beetle and the western balsam beetle, represented with red and orange dots, respectively, cover the Roaring Fork Valley like chicken pox.
Adam McCurdy, forest programs director for the Aspen Center for Environmental Studies, said just about anywhere in the Roaring Valley where conifer trees are dying, it’s a sign of the Douglas-fir beetle outbreak. Douglas fir needles fade, then turn a reddish-orange after an attack.
“That’s kind of been a slow-brewing thing,” he said. “Crested Butte had an outbreak that was pretty slow moving, which is what we’re seeing here.”
Dying stands of Douglas fir are visible in the Fryingpan Valley, on the north side of Snowmass Canyon near Triangle Peak, on the front side of Aspen Mountain and along Highway 82 up Independence Pass, McCurdy said.
A U.S. Forest Service map showing beetle activity areas shows a major infestation south of Frying Pan Road about halfway between Basalt and Ruedi Reservoir. Lesser infestations are in the Upper Fryingpan Valley, north and northeast of Meredith.
The report by the state and federal forest services said Douglas-fir activity was detected on 7,400 acres in Colorado, including 6,000 new acres. The White River National Forest, which includes the Aspen area, was among those where mortality is most evident, the report said.
The western balsam beetle affects subalpine fir trees. There are numerous pockets of infestation on upper Smuggler Mountain and in the Williams Mountains, according to the Forest Service map.
Statewide, the spruce beetle “remains the most damaging forest pest in the state for the eighth consecutive year,” the state and federal forest service agencies reported.
“Since 2000, spruce beetle outbreaks caused tree mortality on roughly 1.87 million acres in Colorado, and about 41% of the spruce-fir forests in the state have now been affected,” the report said. “Blow-down events in Engelmann spruce stands, combined with long-term drought stress, warmer temperatures and extensive amounts of older, densely growing trees contributed to this ongoing epidemic.”
The 2019 survey found evidence of spruce beetle activity on 89,000 acres in Colorado, including 25,000 acres of new activity. So far, spruce trees in the Roaring Fork Valley have avoided infestation.
Forest Service officials expressed concerns last year that the Roaring Fork Valley could experience an outbreak of spruce beetles after so many trees were leveled by avalanches in the epic avalanche cycle in March. The carnage was evident in multiple valleys.
McCurdy said it is too soon to say whether the downed spruce will attract beetles. He noted spruce beetles are always present and looking for susceptible trees.
“Those beetles are native and you find them in our forests at any given time,” he said.
The U.S. Forest Service noted that the avalanche activity throughout Colorado’s mountain last winter created conditions that most be monitored.
“Avalanches were abundant in 2019 and may warrant additional monitoring for bark beetle activity depending on the species and size of trees taken down and in adjacent stands,” the report said.
McCurdy and the report made the point that a second straight winter of average to above average snowfall will benefit the trees by helping them shore up their defenses. However, McCurdy noted that Colorado forests have dealt with several recent droughts, the latest in 2018. In addition, a warming planet poses long-term consequences.
“It’s not like one or two good years can balance out all the bad ones,” he said.
ACES will release its annual report on forest health in the Aspen area later this winter.