An outbreak of spruce beetles exploded across the forests of Southwest Colorado last year, according to the results of an aerial survey released Wednesday.
The outbreak will erase some of the region’s high-altitude stands of trees for many decades.
“The forest is ripe for the beetle to move through,” said Bob Cain, a U.S. Forest Service entomologist.
The drought, dense stands of mature trees and warm winters all make for ideal conditions for the beetles, which bore into trees to feed and lay eggs.
The size of the active outbreak more than doubled in a year. The annual study found spruce beetles active on 311,000 acres, including 183,000 acres that weren’t detected in the 2011 survey. The outbreak has covered more than 1,400 square miles since it began in 1996.
“Even our acre numbers we get from the aerial survey don’t really capture it,” Cain said.
Infected trees often take a couple years to die, so the infestation will look even more widespread by next year, Cain said. Beetles grow to adulthood inside trees and then take off to infect new trees. The flight in 2012 was “enormous,” according to the aerial survey report.
On the bright side, Cain said, many spruce forests are mixed with subalpine fir, which are not affected by the spruce beetles.
But spruce trees regrow slowly. Where the beetles hit stands of pure spruce, most people won’t live long enough to see mature trees return to the site.
Although Colorado has several pockets of spruce beetle outbreaks, the hardest-hit areas are in the Rio Grande, San Juan and Gunnison national forests. The most visible outbreak is along Wolf Creek Pass, but there are even bigger infestations in the Weminuche and La Garita wilderness areas and around the town of Creede.
The U.S. Forest Service and Colorado State Forest Service cooperate on the annual survey. Officials from both agencies used the survey’s release to promote increased logging in beetle-infected areas.
“The spruce beetle epidemic in our high-elevation forests demonstrates the breadth and complexity of issues affecting Colorado’s forests,” said Joe Duda, director of the Colorado State Forest Service, in a prepared statement. “Active forest management and a viable forest products industry will allow landowners and land-management agencies to expand forest treatments on lands available for management while reducing wildfire risk and protecting important natural resources and infrastructure.”
But logging remains controversial. Environmental groups including Rocky Mountain Wild won a lawsuit in early 2012 to prevent logging on 3,500 acres of spruce in Rio Grande National Forest.
Josh Pollock of Rocky Mountain Wild said the beetles are a natural part of the ecosystem, and land managers need to carefully pick the areas they will log, with an emphasis on protecting human settlements.
“Let’s be cautious about having an increase in beetle-killed trees be a reason for harvesting trees deep into the backcountry,” Pollock said.
Elsewhere in Colorado, the mountain pine beetle outbreak slowed noticeably in 2012.
The pine beetle has claimed 3.4 million acres of lodgepole and ponderosa pine since 1996, but the infestation expanded by just 31,000 acres last year, mostly near Fort Collins.