Forests: Spruce beetles spreading fast in southern Rockies

State report details status of insect activities

Spruce beetles are widely active across the mountains of southern Colorado.

Staff Report

FRISCO — Windstorms, mild winters and drought are the key factors in the continued spread of spruce beetles, which have become the dominant change agent in Colorado forests the past few years.

According to the latest annual forest health report compiled by state forest experts, spruce beetles were active across 398,000 acres in 2013, affected more than triple the amount of acreage than mountain pine beetles.

The areas most affected include the San Juan and La Garita mountains, but there was also significant spruce beetle activity on the Grand Mesa, in the Mt. Zirkel and Rabbit Ears ranges, as well as the Wet Mountains and Sangre de Cristo Range.

The 2013 Report on the Health of Colorado’s Forests, was released by the Colorado State Forest Service at the annual Joint Agriculture and Natural Resources Committee Hearing at the State Capitol in mid-February. It details forest health concerns throughout the state and the opportunities available for landowners to mitigate their effects.

“Colorado land managers continue to face unprecedented challenges in their pursuit to foster healthy, thriving forests,” said Mike Lester, state forester and director of the Colorado State Forest Service.

Mountain pine beetle activity continued to die down, with active infestations reported on about 98,000 acres in Colorado. Most of the pine beetle activity has shifted east of the Continental Divide, including 85,000 acres in Larimer
County, representing 87 percent of all pine beetle activity in the state.

Forest managers also documented about 178,000 acres of subalpine fir decline in many high-elevation spruce-fir forests across the state. The mortality is the result of attack by the western balsam bark beetle. Attacks typically occur in trees infected and weakened by two species of fungi that attack the root systems of subalpine fir.

Aspens in some areas were under pressure from insects, with two species at outbreak levels in Colorado last year. Western tent caterpillar (Malacosoma californicum) and large aspen tortrix (Choristoneura conflictana) affected about 54,000 acres in 2013, up from 22,000 acres in 2011.

Affected areas include the Spanish Peaks on the Sangre de Cristo Range; the San Juan and San Miguel mountains; portions of the Culebra Range, including the North Fork Purgatory River Basin; and near Bonanza in the La Garita Range. Significant defoliation from large aspen tortrix occurred in the Wet Mountains and the Roaring Judy Basin near Almont.

The 2013 report also includes a special online supplement, the 2013 Colorado Forest Insect and Disease Update, which is a comprehensive listing of the damaging agents of Colorado’s forests. This supplement is available, in electronic form only, at


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