Bark beetles are devouring trees in the San Juan National Forest, and this may ultimately mean less shade for recreationists in the popular Boggy Draw area near Dolores.
Ponderosa pines are especially under fire, with several different species of beetle now attacking them in the region.
The ponderosas in the San Juan are particularly vulnerable to the tiny but voracious insects. That’s because the stands are densely crowded with trees that are mostly the same age, the result of widespread clearcut logging a century ago.
U.S. Forest Service officials are trying to slow the beetles’ spread but are battling a number of factors.
“We’re doing our best, but there is no silver bullet,” forester Kyle Personett commented during a tour of some affected areas on Oct. 1.
The three beetle species causing the most damage to the ponderosa pines are the round-headed pine beetle, mountain pine beetle, and southwestern pine beetle. They’re all native to the area.
The beetles fly to a tree, burrow into its trunk, and lay eggs under the bark. The larvae then feast on the phloem layer, which contains the nitrogen they need.
The trees can resist the insects by oozing sticky resin to “pitch out” the bugs, but drought and warm temperatures hamper the trees’ ability to do that.
“The ability to pitch out the beetles is based on water availability,” Personett said.
In addition, the combined attack is tough to fight off, as the different beetle species fly to new trees and start attacking them at different times of the year. And the beetles are growing more and more widespread.
“We’re seeing the round-headed pine beetle further north in Colorado than we’ve ever seen it,” said Todd Gardiner, Cooperative Forestry Program manager in the Rocky Mountain region of the Forest Service. “It has come to the Uncompahgre Plateau.”
While beetles normally would be killing only a few old or diseased trees, they are now attacking healthy ones, leaving skeleton stands where there were recently green-needled trees.
In addition to the three pine beetles, ips beetles – one type of which decimated local piñon-pine forests two decades ago – are helping to finish off weakened ponderosa, Forest Service entomologist Matt Ethington said.
“When the trees start to die, the ips move in,” he said.
A serious beetle outbreak is occurring on the Glade just six or seven miles from the northern end of the Boggy Draw area. Forest Service officials are worried that the beetles may soon spread there. Although they aren’t able to fly long distances, they can be carried by the wind.
To try to halt or slow the beetles’ spread, Ethington said, the Forest Service cuts down trees that are beetle-infested.
A longer-term solution is to thin stands of ponderosa. This leaves more moisture for the remaining trees. It also opens up areas where ponderosa saplings can begin to grow, creating some age diversity.
“Younger trees are more resistant to insects and disease,” Personett said.
When a dense stand of trees that are all the same age is attacked, the whole stand can be wiped out. “There’s no new trees to take their place,” said Ethington. “There may not be enough to keep it a pine landscape.”
But thinning the stands requires help from an active timber industry.
The Forest Service has approved timber sales in the Dolores Ranger District, but not all are being actively logged.
“Part of the problem is cost,” Gardiner said. “The biggest cost is moving material to the mill. If you have to move it more than 50 miles, you’re usually spending more to move it [and eliminating profit].”
Some mills want only wood that has not been affected by insects, he said, while others will take downed timber.
Ethington said if there is no market for the harvested ponderosa, enough logging won’t happen and the beetle problems will continue.
And when a large number of ponderosa pines are killed by beetles, Gambel oak will likely take over. Gambel oak is deep-rooted, highly resilient, and resistant to fire. It takes regular fires occurring every five to 20 years to keep oak down, Personett said. The Forest Service does utilize prescribed fire to try to maintain forest health, but he said it’s “a blunt tool.”
The future of the ponderosa forests that characterize much of the lower elevations of the San Juan National Forest is definitely uncertain.
As climate change makes temperatures warmer, it might be thought that ponderosa pines could move upward in elevation. But Personett said that is unlikely to happen because the pines’ limbs break easily under loads of snow.
“The ponderosa-pine band is narrow [in elevation],” he said.
So, in the future, cyclists may be pedaling through oak forests in the Boggy Draw area rather than under the welcoming shade of ponderosa trees.
