What's threatening the forests?
- Aspen diseases
For the third year in a row,
unexplained aspen decline occurred in western Colorado. Experts have not determined what is killing the trees and their root systems. Preliminary assessments show many different causal agents.
The Marssonina fungus causes the most common disease on aspen
foliage. Although there is leaf
discoloration, this condition usually
is not damaging. Heavy infestations will cause early leaf drop.
Phellinus igniarius decay fungus enters though old branch stubs or other wounds. Affected trees often are used by hole-nesting birds.
The wood-boring beetle lays eggs on the bark of the aspen. The larvae then tunnel, weakening the wood. Entry and exit holes of the beetle invite fungi, which can result in limb breakage.
The slowly developing canker is caused by the fungus Ceratoeystis fimbriata and is easily recognized. The canker rarely kills the tree because of its slow development.
- Spruce beetle
Like the mountain pine beetle, the spruce beetle has been killing trees across Colorado for decades. Aerial surveys show the current spruce
beetle problem affected about 97,000 acres across Colorado in 2007, up from 68,000 acres in 2006.
A tremendous loss of spruce and aspen trees could make up the next chapter in the drastic transformation of Colorado's forests after the mountain pine beetle eats itself out of house and home.
The spruce bark beetle continues to linger at concerning levels after windthrow events toppled spruce trees across the state, providing an ideal breeding and feeding ground for an outbreak of the pest that has always existed in Colorado's forests.
Doug Allen will never forget his up-close and personal encounter with one such event - a calamitous storm later dubbed the Routt Divide Blowdown - that kick-started the local spruce beetle boom on the afternoon of Oct. 24, 1997.
Allen, vice president of mountain operations for Steamboat Ski and Resort Corp., needed a drawing that was on the Thunderhead peak of Mount Werner. With most mountain crews off for the afternoon, Allen hopped in a truck to go get the drawing himself.
Allen first noted a strong wind and then the clouds. As he made his way up Burgess Creek Road, it started to snow incredibly hard.
"It was pretty wild," said Allen, who recalled the afternoon on a drive up Mount Werner earlier this summer.
Despite the weather, Allen decided to press on.
"I thought I'd just grab the drawing and run," he said.
But it wasn't long before drifts started forming on the road.
"I got to the point where I could not go any farther," Allen said. "As I was coming down the hill, you could hear the trees snapping."
In what the U.S. Forest Service would call the largest known forest blowdown ever recorded in the Rocky Mountains, the storm took down 20,000 acres of old-growth forest in a stretch several miles wide and 20 miles long in the Mount Zirkel Wilderness Area and Routt National Forest.
Despite the heavy snow, Allen remembers the road was brown with an uncanny amount of needles being blown from the trees as he escaped the mountainside unharmed.
The downed trees helped set the stage for a spruce beetle infestation. The separate and unrelated mountain pine beetle epidemic since has eclipsed the spruce bark beetle by more than a million acres, but land managers warn a tremendous loss of spruce trees could be forthcoming.
While efforts to halt the spruce bark beetle's spread in Northwest Colorado - including on the slopes of Mount Werner - have proved mostly successful, the infestation is spreading in other parts of the state, said John Twitchell, a Steamboat Springs-based forester with the Colorado State Forest Service.
"There's still pockets of it in North Routt," Twitchell said. "It's still a concern."
According to the 2008 Northwest Colorado Forest Health Guide, windthrow events in southern Colorado - like the Routt Divide Blowdown before them - have set the stage for booming populations of spruce bark beetle. The spruce bark beetle infestation encompassed about 97,000 acres in 2007, up from 68,000 acres in 2006.
A spruce bark beetle epidemic could be more devastating to Colorado ski areas than the mountain pine beetle because most resorts' upper reaches are in spruce forests, according to the forest health guide. Researchers are concerned about studies that show a trend in the beetle that has shortened its lifespan from two years to one. This allows the beetle to propagate more quickly.
Aspen trees also are under attack statewide. Aerial surveys showed 334,000 acres of aspen decline and mortality in 2007, the third year in a row of unexplained aspen decline in Colorado.
"Certainly there's a lot of concern about our aspen, another very important tree to our scenery," Twitchell said. "What I see (in Northwest Colorado) is a lot of problems with the aspen. But I also see it sprouting real well. Other parts of the state are concerned because they're not seeing the regeneration."
The forest health guide says researchers are designing a study to determine the specific symptoms and causes of aspen decline.
"If aspen root systems are unable to produce new aspen suckers, aspen clones that have existed for millennia will be lost," the forest health guide says.
Although aspen decline and spruce beetle - along with fir decline and the ips bark beetle - present a challenge for land managers and owners, Twitchell doubts these forest health issues will ever pack the punch of the mountain pine beetle.
"I'm not making any predictions," Twitchell said, "but that's not what I'm seeing."