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Why are some of Colorado’s aspen trees brown? An expert says, 'The precipitation kind of turned off'

Posted at 3:50 PM, Sep 02, 2020
and last updated 2020-09-03 07:25:06-04

KENOSHA PASS, Colo. — Along the scenic drive through the Pike National Forest, aspen trees line Highway 285 between Grant and Jefferson. But some of those trees are not covered in their usual green-about-to-turn-yellow leaves. Many of them are brown and dead.

Several Denver7 viewers and employees noticed this on their weekend treks into the mountains, and raised the questions of "Why?" and "What does that mean for leaf-peeping season?"

Dr. Dan West is an entomologist with the Colorado Forest Service, specializing in trees and tree issues. He blamed the issue on drought and bugs.

“As they no longer have enough water, the tips (of the leaves) start to burn and we see this brown margin or the outside edge of the leaf turns brown,” he said.

The entire state of Colorado is seeing some form of drought, according to the U.S. Drought Monitor. Conditions in many of the mountains west of Denver are dealing with "severe" or "extreme" drought.

“The precipitation kind of turned off,” West said.

The other factor that Colorado’s aspens are dealing with are bugs.

“What we’re seeing more of are defoliating insects,” he said. “So these are caterpillars and beetles that feed on the leafs of aspen.”

In many other years, brown spots have appeared on many aspen leaves as a result of fungus that is native to Colorado. Since that usually requires a wet spring, that problem is actually less common this year. But the drought/insect combo is still causing some issues.

“Trees are stressed so they’re likely to shut down their processes slightly earlier. That’s why we’re anticipating some of the fall foliage colors, the show, to be slightly earlier by days,” West said.

So West says you may want to push your leaf-peeping plans up by a few days, but not cancel them entirely.

“One given stand or drainage (group of aspen trees) might not look great but the next drainage might be the best it’s ever been because of adequate snowpack,” he explained.

So while the early signs may not look great, the science points to fairly full fall foliage.

“I think this is still gonna be a fantastic year. I don’t know if I’d say its going to be a ten (out of ten) but I certainly think we’re gonna be above average and slightly earlier than average,” West said.

Denver7 has published a full guide of the best places and times to see fall foliage in Colorado here.