Bark beetle outbreaks expand in Colorado

Tuesday, January 22, 2019

BUENA VISTA, COLORADO — Bark beetle outbreaks have continued to expand in parts of Colorado, based on a 2018 aerial forest health survey conducted by the Colorado State Forest Service and the U.S. Forest Service, Rocky Mountain Region. 

The agencies work together to aerially monitor the state’s forests every year.

It was the seventh consecutive year that spruce beetle populations caused widespread tree mortality. For Engelmann spruce, which spruce beetles have been attacking, 178,000 acres were affected across the state last year, including 59,000 acres that were previously unaffected.


Primary areas impacted include forestlands in and around Rocky Mountain National Park and portions of the San Juan Mountains, the West Elk Mountains and the Sawatch Range.

In Chaffee County, spruce beetles are affecting 7,500 acres of forest, which includes 2,000 new acres.

The affected acres only take into account trees that are currently being affected and not the ones that have already died. Since 2000, spruce beetle outbreaks have caused tree mortality on more than 1.8 million acres in Colorado, affecting approximately 40 percent of the spruce-fir forests in the state.

When added with the damage mountain pine beetles have caused to the state’s forests, the number of acres jumps to 5.2 million, roughly one-fifth of the state’s 24.4 million forested acres.

Spruce budworms are affecting another 7,000 acres of forests, mostly Douglas fir, in Chaffee County. The budworms are defoliators, feeding on leaves, and can take four to seven years to kill a tree, compared to spruce beetles that kill a tree in a year or two tops. Budworms, however, reduce the overall health of trees, making them more susceptible to other insects and diseases.

A couple of factors that added to last year’s outbreak were the drought and high temperatures.

Dan West, State Forest Service entomologist, said it was the second driest year since they began tracking in 1895. In that same period, West said it was the warmest year on record.

“We no longer have climate control on beetles,” West said.

Trees normally turn water into resin and that resin can push bark beetles out.

“In dry years, there’s not enough resin to push (the beetles) out of the wound,” West said. “They’ll try to mass attack trees to get by its defenses.”

West said the beetles go after big trees first because they have more carbohydrates. Then, by feeding perpendicular patterns, they cut off the trees’ nutrient flow and kill them.


To combat the insects’ spread, West said they use chemical treatments to protect individual trees. The chemicals produce pheromones that tell the insects to go to a different tree. “We use chemistry against them,” West said. “It tells them to go somewhere else, this tree is full.”

Thinning forests also reduces the spread since the beetles aren’t great fliers and the extra wind can also scramble the signals they send to each other.

“They don’t like open, light stands,” West said. “They don’t like to fly through them, and the wind patterns jam up their communication.”

Wet, cold years would also help. West said the snowpack in the Arkansas River Basin is at 121 percent, but it needs to stick around instead of melting really fast in the spring to help the forests access the water.

“We need a slow warm-up in the spring so it slowly melts off,” West said.

One thing individuals can do, West said, is work with their local foresters to make sure their stands are healthy.

The problems the beetles are causing extend beyond the dead trees.

“Bark beetles affect everything every day,” West said. “The snowpack runs off earlier so it affects drinking water. When the snow comes off sooner, the trees have a longer period to green up and grow, but then they cure earlier so we get wildfires earlier. Once they fall down, it changes (the fuels), so fires are also burning more intensely and hotter.”

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