San Juan National Forest officials are becoming increasingly concerned about the destructive impacts of a round-headed pine beetle infestation.
The beetle is native to the state but is more commonly seen in New Mexico and Arizona. As it spreads northward into Southwest Colorado, ponderosa pine are on the menu.
Of the 90,000 acres of manageable ponderosa stands in the Dolores District of the San Juan forest, 10,584 acres have been infested or killed primarily by the round-headed pine beetle since 2011, according to forest officials and a state entomologist.
In 2011, 8 acres of ponderosa infested or killed by the pine beetle was detected in the Lake Canyon and Narraguinnep Canyon in Dolores County.
In 2013, the area of beetle killed and infested trees had spread to 1,478 acres in that area, then to 6,643 acres in 2016. By 2017, aerial surveys showed 10,584 acres of ponderosa have been killed or infested by the beetle, mostly in the Glade area along the eastern rim of the Lower Dolores River canyon.
Insect traps and tree damage patterns specific to the bug identified the round-headed beetle as the main culprit, but the mountain pine beetle is also to blame. There is another pine beetle infestation in Lone Mesa State Park to the east.
“What we’re seeing now are small pockets in other areas being impacted by the beetle, including one in the Cherry Creek area,” said Dolores District Ranger Derek Padilla at a recent Montezuma County commission meeting. “We’re focusing our forest treatment plans to hopefully slow their progress.”
The relatively large and sustained infestation by the round-headed beetle is a new phenomenon for Colorado, and somewhat of a mystery, said Dan West, an entomologist with Colorado State Forest Service during a recent PowerPoint presentation. The oldest, most knowledgeable people on the topic don’t recall something like this happening in our area, he said at a talk hosted by the Dolores Watershed and Resilient Forest group.
Typically, round-headed beetle outbreaks will cause tree mortality in a forest for 2 years, then dissipate the third year. Why this extended infestation is occurring for much longer is unknown, West said.
One possibility is that recent drought conditions that have weakened the tree’ defenses against the beetle. Also, over-stocked forests in the area create weaker trees as they compete for sunlight and limited water.
Adult round-headed pine beetles fly from host trees in October and November and attack new trees causing mortality if the tree is weak. They lay eggs that overwinter and hatch around March then mature in August.
Officials are conducting studies on whether the beetle is managing to have two life cycles within one year, which if true would partly explain the insect’s rapid impact.
West said more moisture and healthier trees would help by flushing pitch tubes with more resin that push beetles out.
David Casey, a forester with the San Juan National Forest, said they are addressing the beetle kill problem on multiple fronts, but are hamstrung by an insufficient ponderosa timber market.
At the site of the main outbreak, dead trees are being removed and there are ongoing timber sales, including for firewood.
Officials said by the time the firewood is removed and stacked for the public, the beetles have already left, so there is no danger of spreading it. There is also a niche market for beetle-kill trees because they have a blue-stain fungus that can add value to decorative wood products such as paneling and furniture.
On lands adjacent to the beetle outbreaks, more thinning, prescribed fire and timber sales are being planned to improve forest health and prevent the infestation from spreading. The worry is that swaths of dead trees left standing will create conditions for a larger wildfire.
“The conundrum we’re running into is we don’t have a strong enough timber market to haul the amount trees that need to be cleared,” Casey said. “For us to do it is too expensive.”
The Colorado State Forest Service recently spent $50,000 masticating beetle killed trees in Lone Mesa State Park. There is also some logging going on in the Cherry Creek area to mitigate the beetle outbreak there.
There has been some interest in logging larger quantities of local ponderosa pine, Casey said, including a tour by a large mill from Montrose this summer. They harvested test trees for one of their mills, and reported the wood to be good quality. But so far no large commitments have been made.
Casey said the Dolores District of the San Juan forest has 4,000 acres of Ponderosa timber sales ready to go if a larger mill is interested.
“The forest industry component is the key to a healthier forest that’s more resistant to disease, insects and drought,” he said. “A stronger timber market would allow us to get out in front on thinning of overstocked forests. Right now, there is no one to take the volume of trees that need to be removed.”