Colorado State Forest Service: Larimer County Saw Greatest Bark Beetle Impacts in 2011

The Colorado State Forest Service and U.S. Forest Service this week released the results of an annual aerial insect and disease survey in Colorado, which indicate that the most significant forest health concern continues to be the spread of the mountain pine beetle. For the second consecutive year, the northern Front Range experienced the highest mortality rates affecting ponderosa, lodgepole and five-needle pine trees. In Larimer County alone, 587,000 acres showed some level of active infestation last year.

More than 3.3 million acres have been impacted by mountain pine beetles in Colorado since the first signs of the outbreak in 1996. Although an additional 140,000 acres of tree mortality due to the beetles were detected across the state in 2011, the epidemic has slowed down in many areas. Foresters and land managers are now focused on the removal of standing dead trees that pose a threat to human safety.

Jeff Jahnke, state forester and director of the Colorado State Forest Service – a service and outreach agency of the Warner College of Natural Resources at Colorado State University – said that ongoing forest management can help prevent such extensive insect outbreaks in the future.

“Active forest management on both public and private lands can lead to healthier trees on the landscape and create the diversity necessary to reduce future large-scale insect epidemics,” Jahnke said. “If we don’t plan now for ongoing management of these forests, we will set the stage for another mass disturbance like the current bark beetle epidemic.”

The aerial survey data also indicated that spruce bark beetles continued to spread at higher elevations, especially in southern Colorado. Statewide, 262,000 acres were detected with tree mortality in 2011, which brings the total affected acreage since 1996 to 741,000.

Sudden Aspen Decline (SAD), which was highly visible on the Western Slope for several years, now appears to have subsided. Field observers noted that many aspen stands once considered dead are showing some new sprouting, and plant pathologists and entomologists don’t anticipate large-scale mortality in aspen this year as a result of SAD.

To view the full aerial survey results, go to