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Douglas Fir Beetle Threatens Area Trees

Oct 18, 2018

Patches of Douglas firs on Aspen Mountain have been killed by a bark beetle. City officials are working to mitigate the fire hazard the dead trees present and prevent the insect's spread.
Credit Elizabeth Stewart-Severy / Aspen Public Radio

At the foot of Aspen Mountain, just off the Ajax Trail, several towering Douglas fir trees have turned brown-red and dropped their needles. They look like red ghosts in the evergreen forest.


"A lot of these trees have been attacked by the douglas fir beetle, a relative of the pine bark beetle," said

Adam McCurdy, Forest Programs Director for the Aspen Center for Environmental Studies. He explained it’s normal to see some beetles; they are natives, a part of the natural process.

Typically the beetles would only attack trees that are damaged by fire or wind-throw, not an otherwise healthy stand. But in a drought year like this one, these patches of beetle-eaten douglas firs pop up more often, and they’re presenting a host of issues.


City of Aspen Forester Ian Gray explained that not only are the dead trees an eyesore, they’re also hazardous, dry fuel.  

“Having an overly dense forest that suddenly dies off and creates a bigger wildfire risk, that’s a concern,” Gray said.

Crews have removed about two dozen dead douglas firs as part of a wildfire mitigation project. The trees are also dangerous to anyone hiking or running on the Ajax Trail.

Tunnels called galleries mark where Douglas fir beetles consumed this tree's nutrients, killing it.
Credit Elizabeth Stewart-Severy / Aspen Public Radio

Downed trees dot the trail, their rough bark fallen away to reveal the beetles’ destruction. The log is covered in tiny tunnel marks called galleries. It looks like a topographical map, wrapping around the entire trunk, and it’s clear evidence of how the beetles work.


“It stops the flow of nutrients and water, so essentially chokes the tree, girdles it and kills it,” Gray said.

Gray is working to reduce the spread of the beetles using pheromone packets on trees in key spots. These use the beetles' own chemicals to keep them from spreading to nearby trees.


"It sends the message to the bugs: hotel's full, go somewhere else," he said.

It’s not feasible to use those chemicals across entire forests, but Gray is still hopeful that douglas fir beetles won’t totally decimate the local landscape.


“Douglas fir beetle is a bit more patchy, sort of goes in pockets, doesn't hit every single tree in the stand," Gray said.

Gray has identified the beetle as a priority threat in the city's most recent forest management plan and is working to strike a balance of managing the damage and picking a few key spots for focused prevention efforts.