The beetles killing spruce trees in epidemic proportions across Colorado attacked forests at a faster pace in 2014.

Meanwhile, the mountain pine beetle epidemic slowed dramatically, likely because the pine beetle has run out of live trees to infest.

The U.S. Forest Service and Colorado State Forest Service on Friday, Feb. 6, released the results of their annual aerial survey of insect- or disease-killed trees across nearly 44,000 square miles of Colorado forests.

The spruce beetle outbreak was detected on 760 square miles last year, compared with 625 square miles in 2013. The epidemic expanded to 395 new square miles in 2014, as compared with 338 previously unaffected square miles in 2013.

The spruce beetle epidemic is expanding most rapidly in southwestern Colorado’s forests.

Statewide, the total area affected by the beetle since 1996 has increased to about 2,200 square miles, or roughly 10 times the size of the Eagles Nest Wilderness which lies in Summit and Eagle counties.

Researchers say a combination of drought, warmer winters, high-wind events and large amounts of older trees growing close together have intensified the beetle outbreak.

The mountain pine beetle epidemic continued to decline in 2014 to its lowest level of active infestation in 17 years.

Statewide, the mountain pine beetle was active on 23 square miles last year, compared with 153 square miles in 2013. About 5 square miles of new infestation were detected in 2014, versus 14 square miles of newly impacted trees the year before.

Active acres are those that may be impacted over multiple years, while new acres are those not previously impacted in the current epidemic.

The mountain pine beetle outbreak has affected about 5,300 square miles total in Colorado since 1996, Forest Service officials say.

Though spruce and pine beetles are related, the two insects mostly attack only the type of trees they are named for. Both kill trees by destroying the thin layer of tissue below the bark that transports nutrients.

Beetle outbreaks are natural occurrences, and the trees and beetles have evolved together over millions of years.

Additionally, researchers found that 122 square miles of aspen in Colorado in 2014 were impacted by defoliators, such as the western tent caterpillar.

The caterpillar defoliates aspens and can kill trees if present over multiple consecutive years, especially during drought.

“The broad extent of insect and disease activity revealed by this survey demonstrates the critical need for partnerships to address forest health threats across ownership boundaries,” said Mike Lester, director of the State Forest Service. “Just like wildfires, these threats don’t stop at property lines.”

While the U.S. Forest Service takes action on public national forest lands, the State Forest Service works with private landowners to help them meet their forest management goals.

Both agencies aim to sustain forest ecosystems and protect forested watersheds, and they measure their progress in the reduction of large-scale wildfires, timber harvested and the amount of forest treated with management practices.

The Rocky Mountain Region of the U.S. Forest Service is increasing the pace and scale of forest management in Colorado.

Each national forest is stepping up forest treatments, and many are working collaboratively to plan and apply work to the areas most affected by the beetles.

Dan Jirón, regional forester for the Rocky Mountain Region, said the Forest Service is working with local and state partners, including the wood-products industry, on the forest areas heavily impacted by the beetles with clear-cutting, logging and other methods.

In addition to dozens of shorter-term stewardship contracts, the Forest Service awards 10-year contracts to remove dead trees.

On the White River National Forest, which includes much of the land in Summit County, foresters awarded a long-term contract to hauler West Range Reclamation in November 2012 to remove 1.5 square miles of trees a year.

The hauler has a 20-year contract with Eagle Valley Clean Energy, the woody biomass plant in Gypsum.