The forests of Southwest Colorado may be facing yet another new and highly destructive threat: the pine beetle.

“It’s not completely unexpected, but it’s worrisome,” said Gretchen Fitzgerald, a forester for the U.S. Forest Service’s Columbine District, which manages nearly 700,000 acres of the San Juan National Forest in La Plata and San Juan counties.

Over the past two decades, more than 120,000 acres of the Weminuche Wilderness – Colorado’s largest designated wilderness area at 488,210 acres – have fallen prey to the destructive spruce beetle.

In its wake, the spruce beetle has left vast areas of dead trees, most visible over Wolf Creek Pass. However, the spruce beetle, for the most part, targets only Engelmann spruce at elevations of about 9,000 feet.

The pine beetle, on the other hand, is another destructive force all its own.

From 1996 to 2016, the pine beetle ripped through more than 3.4 million acres of Colorado’s forests – about 14 percent – according to the Colorado State Forest Service, by far the state’s largest infestation.

However, the majority of forests affected by the pine beetle were in northern areas of the state. Southwest Colorado, for the most part, has been relatively unaffected by Colorado’s most harmful tree pest.

That is until recently.

The Forest Service’s Fitzgerald said an annual survey of an area by Vallecito Lake, northeast of Durango, found that a number of ponderosa pine trees appeared dead because of beetle kill.

“We did what we could do to remove the population there, but it made me concerned the beetles may be increasing up there,” she said. “We just haven’t seen too much pine beetle on the Columbine District.”

Upon further inspection, it turned out there were three subspecies of bark beetle that appeared responsible for the kill-off.

The western pine beetle hit the tree’s main body. The ips beetle worked on the top of the tree, as well as its limbs. And the red turpentine beetle ate away at the base of the tree.

“Any one of those beetles don’t necessarily do enough to kill a tree, but when they all get together, you start seeing mortality,” Fitzgerald said. “The length and number of different kinds of beetles attacking all at once is unprecedented as far as we know.”

This particular kill-off is a new discovery for forest managers in this region, which prompted other surveys that found the pine beetle at work near Rockwood, Junction Creek and Falls Creek.

Kent Grant, a district forester with the Colorado State Forest Service, said Southwest Colorado has seen periodic outbreaks of pine beetle, but current conditions in the forests here have spelled out a sort of perfect storm.

Most of the ponderosa trees at risk are more than a 100 years old in densely forested areas.

“When trees are getting older, and at the same time competing for sunlight, nutrients and moisture, they’re stressed and easier targets,” Grant said.

Plus, Grant said the effects of climate change are added to the mix: warmer winters translate to longer seasons for beetles to take their toll, and drought weakens a tree’s ability to defend itself.

“Bark beetles are native, but when the conditions are right, then that’s when we start to see more and more tree mortality,” he said.

And with climate change, “we’re not used to seeing this kind of mortality.”

Unfortunately, there’s not much in the way of preventing a beetle outbreak. Certain steps, such as thinning and prescribed burns, can hold off a massive die-off, but those costly measures can work only for so long.

“It’s grim news,” Grant said, “but it’s just a fact.”

Fitzgerald said at this point, the pine beetle activity is not at an “epidemic” level, but it’s worth keeping a very cautious eye on. The Forest Service is evaluating its options to get out on the front end.

Some good news, she said, is that there are tree stands in the area that seem to have fought off the pine beetle’s attack.

In the meantime, Fitzgerald said people need to be aware that cutting wood could attract beetles at certain times of the year. And, it’s important that recreationists do not damage any trees, thereby making them easier prey for beetles.

“So far, it’s natural,” Fitzgerald said. “I just don’t want it to get any bigger.”

jromeo@durangoherald.com