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Fall colors face unknown threat

Alex Miller
Preston Utley/Daily file photoAspens are just about the only tree in the High Country that turn color in autumn, attracting hordes of leaf-peeping tourists, and their money, to the mountains.
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EAGLE COUNTY ” While mountain pine beetles continue to ravage large swaths of forests in the West, the region’s aspen groves are falling prey to an unknown disease that could wipe out 10 percent or more of the iconic trees.

Dale Bartos, an ecologist with the U.S. Forest Service’s Rocky Mountain Research Station in Logan, Utah, said it’s not clear what’s causing the problem with the aspens, although unlike the beetles killing the pines, the aspens are likely being attacked by some kind of disease.

“It’s something we don’t understand,” Bartos said. “I could speculate, but I’d probably be wrong. It’s something we need to address.”



Unlike many trees and plants, aspens don’t reproduce sexually but, rather, through cloning from new shoots ” called “suckers” ” emerging from within their interconnected root systems. Bartos said researchers are seeing the trees’ clones dying off completely so that stands can’t regenerate themselves.

Cal Wettstein, district ranger for the Minturn- and Eagle-area districts of the Forest Service, said he’s seen the aspen phenomenon locally.



“Oh yeah, it’s pretty widespread across the entire West,” Wettstein said. “In the Vail Valley, I’ve seen a lot of aspen mortality up in the Flat Tops (wilderness area) last week; a lot of trees that just didn’t leaf-out this spring or last.”

Near Vail, Wettstein said one need only go a mile or two up the Davos Trail in West Vail to see dying aspens.

Wettstein echoed Bartos in saying he didn’t know why it was happening, but said the aspen is a very complex species compared to the conifer trees.



“There are so many factors,” he said. “We see a range of conditions, like in some places we’ll see where mature trees have died and think it could be drought. Then we’ll see a good crop of sprout from the roots, and other places where there’s nothing coming up from the roots.”

Wettstein said people won’t like looking at dying aspens any more than they like seeing pine trees turning red and succumbing to beetle infestation. But it helps to understand that the forest is in a constant state of change, he said.

“And it does it on a different time frame ” hundreds of years instead of decades,” he said. “It’s difficult for humans to understand.”

Another thing to keep in mind, Bartos said, is that aspen is a “disturbance species,” which means it does well with adversity.

“It needs to be killed to survive,” he said. “Parent trees are knocked back by being burned or cut or they die from something, and then the suckers regenerate to replace the old ones.”

If that suckering doesn’t take place, then new trees don’t grow ” and this is one of the problems in the West. But other things factor into the decline in the region’s aspens.

Aggressive fire management over the past century contributes to the problem, Bartos said. That’s in part because the trees thrive after a fire, and because putting out fires encourages conifer growth, which in turn pushes out the aspen.

“This has been going on for many years, and there’s a big push to restore aspen in certain areas,” he said, referring to programs in the Bridger-Teton National Forest in Wyoming and another one in Northern California.

Locally, Wettstein said a number of projects aimed at rejuvenating aspen stands are ready to start.

Mostly, he said, that means cutting some mature trees to stimulate the suckering, which rejuvenates the clones.

“The difficulty we have now is that, when we started this planning process, we didn’t see the level of dead pine we’re seeing now, so we know we need more planning,” he said.

The original plan, he said, was to go above West Vail and Intermountain to cut some of the lodgepole around the aspen clones to stimulate expansion. By looking at photos of the area from the 1930s, Wettstein said, they can see how much pines have encroached into aspen areas over the ensuing decades.

“A lot of time, aspen have roots under the pine stands, and they’re just waiting for the space,” he said. With pine mortality high, it could give aspen a bit of a boost even as the unknown disease takes its toll in other ways.

Whatever steps can be taken to help the aspen, Wettstein acknowledges that there’s only so much that can be done, given the millions of acres of aspen trees in Colorado alone.

“We’re focusing on the urban interface,” he said, referring to trees close to town. “The other immediate need is to control fires when they happen.”

Aspens are good to have mixed in with the pines, Wettstein said, since they’re less flammable.

“We want a good mosaic of aspen stands and different-aged lodgepole (pine) started, so we have a better mix to withstand fire,” he said.

As aspen stands diminish, it’s not hard to imagine what effects that might have on the forest and the animals and humans that depend on it. In the High Country, aspens are just about the only tree that turn color in autumn, attracting hordes of leaf-peeping tourists, and their money, to the mountains.

For animals, aspens provide food for species such as ruffed grouse, rabbits and larger critters such as deer, elk and moose. Thick stands offer habitat and cover for species from birds to bears.

In the Vail area, Wettstein said aspen stands thrive in slide areas, and help prevent future slides by stabilizing the ground with their roots. The sprouts of the trees, he said, are important feed for elk and deer.

“It’s fair to say the forest will look a lot different,” Wettstein said, referring to the aspen and pine trees dying in large numbers. “We’ll see drastic changes in the coming decades, and I guess it depends on your values, if we think that’s good or bad.”

For more information on aspen restoration projects, go to http://www.fs.fed.us/rm/aspen/

Alex Miller can be reached at 970-748-2931 or at amiller@vaildaily.com.

Vail, Colorado


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