Another 338 square miles of high-altitude forests in Southwest Colorado fell to the spruce beetle outbreak in 2013, according to an aerial survey.
The bugs are now entrenched in San Juan National Forest. They have consumed more than 85 percent of the spruce-fir forest in Rio Grande National Forest, where the outbreak began, said Mike Blakeman, of the Forest Service.
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 around the worst years of the drought around the year 2000 is all but over. The survey found only 2 square miles of new aspen decline statewide.
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.