ASPEN - A survey by the state and federal forest services show that the mountain-pine-beetle epidemic slowed in Colorado in 2012 but the spruce-beetle infestation is expanding. That has implications for the Roaring Fork Valley, according to experts.
The high-elevation forests of the Roaring Fork Valley dodged the mountain-pine-beetle outbreak for the most part. The beetle targets lodgepole pine trees. The forest tree species are more diversified in the Roaring Fork River basin than in such places as Eagle County around Vail, Summit County around Silverthorne and Grand County around Winter Park.
However, the valley's high-elevation forests do feature a substantial amount of Engelmann spruce trees, said Tom Eager, an entomologist at the U.S. Forest Service's Gunnison Service Center. It's not a question of whether the mature and overmature stands of spruce forests in Colorado's central mountains will succumb to spruce-beetle epidemics, it's a question of how soon, according to Eager. And that means changes to the landscape.
"People like big, old, dense stands of trees. That's what beetles like, too," Eager said.
An annual survey by the U.S. Forest Service and Colorado State Forest Service found the spruce-beetle outbreak was detected on 183,000 additional acres in 2012. The total acreage affected in Colorado since 1996 is 924,000 acres, the survey report said.
The mountain-pine-beetle outbreak is better-known because it's bigger and has wrought high-profile damage along Interstate 70. The survey showed that the mountain pine beetle affected only 31,000 additional acres in 2012. That is down from 140,000 acres affected in 2011. The infestation has destroyed lodgepole pine trees on 3.4 million acres in Colorado since 1996, the report said. The beetles essentially are eating themselves out of house and home.
"Most mature lodgepole pine trees have now been depleted within the initial mountain-pine-beetle epidemic area," the report said. "However, the infestation remains active from Estes Park to Leadville."
The emerging spruce-beetle epidemic is most active in Rio Grande National Forest around the town of Creede and in the San Juan National Forest in the southwestern part of the state.
Spruce beetles also have destroyed trees on about 3,000 acres in the Baylor Park area of the White River National Forest south of Glenwood Springs. Hundreds of trees blew down in high winds in Baylor Park in 1999. Spruce beetles feasted on the weakened trees. The trees after others are blown down are like "McDonald's hamburgers on a plate," Eager said. Once the number of beetles exploded, they attacked live trees and overwhelmed them.
"The beetle did really kill a lot of big, beautiful trees" in Baylor Park, said Jan Burke, a silviculturist, or tree expert, at the White River National Forest supervisor's office. "But the activity kind of laid down there four years ago. It really plunged. I'd like to take credit for it, but I can't."
But both Burke and Eager said a spruce-beetle infestation is still likely to occur in the spruce stands of the Roaring Fork River drainage, even if an outbreak didn't spread from Baylor Park. The beetles are always living in the forest, Eager said. They need an event, such as a "blow-down" from strong winds or drought, to spark an infestation.
"They're always out there," he said. "I like to call them the Jekyll-and-Hyde insect."
Here's how Eager described the process: Spruce beetles are typically scavengers that survive by living on limbs that fall off spruce trees or on dying trees. They find enough food to get by. When there is an influx of food, their numbers increase exponentially, and they attack living trees.
Living spruce trees produce resin to fend off the beetles, Eager said. But in warm, dry conditions, there isn't enough water for the trees to produce resin in the amount necessary to defend themselves from the beetles.
Mountain residents and visitors often get upset about the beetle outbreaks because they mean big changes in the appearance of the forests they know and love, Eager said. But spruce forests need the beetles as much as the beetles need them, he said. The beetles thin out mature stands - usually when they are stressed from warm, dry conditions - and help rejuvenate the forests.
Spruce trees can last as long as 400 years, Eager said. Many of the stands in the Roaring Fork Valley are 150 to 200 years old, which is still mature, according to Burke. They also tend to be the same age, so they are more susceptible to events like beetle infestations, she said.
Engelmann spruce stands are particularly prevalent in areas like the upper Fryingpan Valley. But Burke said she doesn't expect an infestation to strike there any time soon. Subalpine fir stands are in decline in the Upper Fryingpan Valley, she said, so that's helped the spruce stands remain healthy.
On the other hand, the ongoing drought threatens to limit water for trees and make them more susceptible to insects and disease.