Aerial Survey Shows Bark Beetle Damage Still Spreading In Colorado

Bark beetles are continuing to cause widespread damage to Colorado’s forests, according to a new study. The annual aerial forest health survey, jointly conducted by the Colorado and U.S. Forest Services, shows spruce forests are at particular risk.

Spruce beetles damaged 178,000 acres of Engelmann spruce forest last year, the report says. While that’s down from 2017, the Colorado State Forest Service warns that the beetles are continuing to spread to new, previously unaffected areas.

Dan West is an entomologist with the State Forest Service. He said that, here in southern Colorado, the beetles have done significant damage to spruce forests in the Sangre de Cristo Mountain range.

“Really the trend is that it’s still continuing to intensify and it’s continuing to work its way through those forests,” he explained. “I certainly don’t see any reason that I would anticipate that to abate anytime soon -- until we get a little bit more precipitation.”

West said that drought in Colorado has made trees especially susceptible to the bugs, which bore through a tree’s bark to feed on and breed within its nutrient system -- known as the phloem -- ultimately killing the tree.

“The way that trees defend themselves is they basically push those bark beetles out with high amounts of resin,” said West. “Well, in dry years, they just don’t have the availability to build up as much reserves of those resins, and so once they start to deplete that resin source, it’s really difficult for trees to continue their defense.”

The forest service says roughly 40% of the state’s spruce-fir forests have been impacted by the beetles. Other affected areas include Rocky Mountain National Park, the San Juan Mountains, the West Elk Mountains, and the Sawatch range.

The survey also tracked the progress of the roundheaded pine beetle. That insect has been increasingly impacting ponderosa pine forests in southwestern Colorado, and the survey revealed 27,000 acres of damage last year, as compared to 11,000 acres in 2017.

"Colorado’s forests are important to the ecological and economic health of our state," state forester and director of the Colorado Forest Service Mike Lester said in a press release. “Our efforts in partnership with the U.S. Forest Service ensure that we understand the condition of our forests, so we can design the best treatments to enhance forest health.”