Pine Beetles Poised to Decimate Colorado’s Ponderosa Forests

In Colorado, beetles are on the move—and it could have big impacts on mule deer habitat. The insects, mountain pine beetles, are the same ones that destroyed many of the state’s lodgepole forests over the last decade, and they’re now moving into ponderosa stands along the Front Range. The US Forest Service estimates that nearly all adult ponderosa pine trees in the area could die from the beetles in the next several years.A map of the predicted outbreak is equally as grim.

Ecologists point to mild, dry winters as the main driver behind the spread. The beetles are native to the state, but drought conditions in recent years have increased their lethality to ponderosas. Ordinarily, the trees would increase sap production as a natural defense mechanism against the insects; however, a lack of water from several successive years of low moisture has compromised their defense systems, making the trees vulnerable.

Once a single beetle finds a weak tree, it sends out a chemical signal that can draw thousands of other beetles to the tree. The critters burrow in and lay eggs, essentially destroying the ponderosa’s water and sap circulation system. Once the eggs hatch, the larvae continue to carve out more channels, eventually killing the tree and leaving the telltale Swiss-cheese-like markings in their wake.

The beetles can target many species of trees, and they first hit Colorado’s lodgepole forests hard in the early 2000s, wiping out an estimated 3 million acres. Hunters, especially in the north-central part of the state near Rocky Mountain National Park, are used to seeing entire mountainsides full of dead trees as a result—most still standing.

Many of those dead forests also burned in 2020 in the Cameron Peak and East Troublesome fires, the two largest in the state’s history. Both fires burned well into the fall, resulting in hunting closures andrefunds of nearly 3,000 elk and deer tagsin the affected units. About 700,000 acres in total burned that year.

Now, the beetles appear to have shifted focus to ponderosas. Already, the Forest Service has documented growing patches of dead trees on the Front Range, especially on the I-70 corridor and along Hwy 285—and it might be too late to stymie the outbreak.

“This is not just a forest health issue,”says Matthew McCombs, director of the Colorado State Forest Service. “It’s a public safety issue, a water quality issue, and a recreation and economic issue. And it is a challenge that demands action before impacts accelerate.”

While the state is primarily concerned about the increased threat of wildfire from dead trees along the densely populated Front Range, the forests are also important for mule deer and elk. Ponderosa stands provide winter range and cover for elk coming off the continental divide, and mule deer live in the dry, low-elevation forests year-round. The trees provide important shade for the animals, and the beetle outbreak could impact ungulate populations depending on the severity.

To combat the spread, the state isfocusing on private lands and helping landowners with forest management along the wildland-urban interface. To eradicate beetles, sick trees must be felled and burned, or debarked, then covered with plastic and allowed to bake in the sun for several months in the summer. Those are both extraordinary, labor-intensive processes, neither practical on large swaths of public land. Several insecticides are available to protect live, uninfected trees, but their efficacies are a mixed bag. Thus, the state’s pessimistic outlook for ponderosa forest health over the next decade, while the beetles run their course.

Even so, “this is not a time to panic,” says McCombs. “It’s a time to ramp up and take action to reduce the impacts of this outbreak and ensure we never allow our forests to become this vulnerable ever again.”

Looking down the road, the area could look awfully different in the next several years—and the quality of hunting could be impacted as a result.

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