By Logan Smith

(CBS4) — If you like viewing aspen trees as they make Colorado colorful in the fall, we have good news.

But if you like hillside forests of spruce and pine…this may be hard to read.

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Research from the University of Colorado indicates the combined effects of bark beetle disease and subsequent wildfires are suppressing the ability of certain species to grow back.

Independently, the two stressors are bad enough. But the study by CU’s Robert Andrus shows the battle against both is clearly having an affect.

“This combination, the spruce beetle outbreak and the fire, can alter the trajectory of the forest to dominance by aspen,” said Andrus. He conducted this research while working on his PhD in physical geography at CU Boulder but is now a postdoctoral researcher at Washington State University.

The West Fork Complex Fire in June 2013. (credit: CBS)

Andrus studied burn areas in the San Juan range, specifically those of the Papoose, West Fork and Little Sands fires that burned in 2012 and 2013 in Rio Grande National Forest.

Beetle-killed trees (credit: CBS)

He and his team found certain spruce trees were unable to recover from severe spruce beetle outbreak and, within five years, a wildfire. The infestation reduced the number of healthy, seed-producing trees. After the fire, too few seeds were produced to regenerate the forest.

In fact, Engelmann spruce and subalpine fir trees failed to recover in 74% of the 45 sites sampled.

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“Bark beetle outbreaks have been killing lots and lots of trees throughout the western United States,” Andrus said. “And especially at higher elevation forests, what drives bark beetle outbreaks and what drives fire are similar conditions: generally warmer and drier conditions.”

Plenty of ‘aspen gold’ at Purgatory Resort during the fall of 2016. (credit: Scott Smith)

Aspen, however, fared better. The roots systems of Aspen survived fires, and those trees are bouncing back.

“The fact that Aspen is regenerating prolifically after wildfire is not a surprise,” said Andrus. “The surprising piece here is that after beetle kill and then wildfire, there aren’t really any spruce regenerating.”

Aspens may, in fact, eventually dominate burn areas and create a forest of their own.

A forest in the San Juan range of the Rocky Mountains, with dead Engelmann spruce trees alongside live aspen trees. (credit: Robert Andrus/University of Colorado Boulder)

The results of Andrus’s research were published last month in Ecosphere.

More research is needed in the areas farther north, he said, like in the burn area of last year’s East Troublesome Fire.

 

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Logan Smith