Another 338 square miles of high-altitude forests in Southwest Colorado fell to the spruce beetle outbreak in 2013, according to an annual aerial survey of Colorado’s forests.

The bugs are now firmly entrenched in San Juan National Forest. The beetles already have consumed more than 85 percent of the spruce-fir forest in Rio Grande National Forest, where the outbreak began, said Mike Blakeman, a Forest Service spokesman.

With last year’s growth, the outbreak that started in 1996 has grown to more than 1,700 square miles, with an epicenter near Wolf Creek Pass. The West Fork Fire Complex last summer burned through a large swath of beetle kill from previous years.

Every year, the U.S. Forest Service and Colorado State Forest Service conduct aerial surveys to track the spread of various infestations of the state’s trees.

The 2013 survey revealed that afflictions of two other tree species lessened last year.

The mountain pine beetle outbreak – which has received much more attention because it is centered in Colorado’s main ski resort area between Vail and Steamboat Springs – slowed considerably.

Pine beetles have killed more than 5,000 square miles of lodgepole and ponderosa pines since 1996. But last year, the aerial survey found them active on just 150 square miles.

And a die-off of aspen trees that began in the worst years of the drought around the year 2000 is all but over. The survey found only two square miles of new aspen decline statewide.

Dan Jirón, regional forester for the Rocky Mountain Region of the Forest Service, said his agency is working with the state and private industry to improve forest health on an increasing number of acres. State and federal lawmakers from mountain districts have been critical of the Forest Service’s low budgets and slow response to the beetle outbreaks.

“Restoring forest health and resiliency is a top regional priority and is guiding much of the work on the forests. In 2013, these National Forest projects in this region led to enough timber harvested to construct 25,000 homes,” Jirón said in a news release.

The beetles are the primary way that mature spruce stands are cleared out to make way for new trees, foresters say. Although it’s a natural process, the life cycle of a spruce forest can be several hundred years. That means Southwest Colorado’s soaring spruce forests won’t be the same for anyone alive today.

“We can focus on the dead trees and be sad, or we can focus on the new forest coming up under it,” Blakeman said.

jhanel@durangoherald.com