The U.S. Forest Service is concerned that a bark beetle outbreak happening now in Narraguinnep Canyon might make its way to Boggy Draw in Dolores.
“If you go out in the Glade where this damage has occurred, all the pine trees are dead, and you just have this oak undergrowth everywhere. It kind of overtops any of the regeneration of the ponderosa,” said Matthew Ethington, a forest entomologist at the Forest Service.
“So basically what you’ll have is an oak forest.”
In our area, it’s Gambel oak that takes over the forest once beetles kill the ponderosa pines. Gambel oak grows densely and incessantly, which makes recreation – and management – challenging.
“If we want to keep pine forests, we’ve got to do something about this,” Ethington said.
And most people the Forest Service has heard from want the forest to remain ponderosa pine.
The outbreak in what locals and foresters call the Glade dates to 2013, an area 7.5 miles northeast of the Dolores River at the Bradfield Campground as the crow flies, and 15 miles from Boggy Draw.
Over time, the area the beetles are attacking has grown, spanning forests and crossing county lines.
What was a problem in the San Juan National Forest has since spread to the Uncompahgre, Ethington said.
Aerial mapping shows the outbreak area is starting to move east, toward Boggy Draw.
“We’ve never had this combination of beetles be so aggressive in Southwest Colorado, ever, that we know of. It is kind of novel and new, and very concerning,” Ethington said.
There are about 100 beetle species native to Colorado. Three are concerning in this region: the mountain pine beetle, southwestern pine beetle and roundheaded pine beetle.
Since they’re native, some level of beetle activity is endemic, or normal. Typically, beetles burrow in older trees that are already dying or diseased, and kill them.
But the bark beetle population is so great, they’re now able to attack and kill healthy trees.
In fact, the vast majority of trees that are dying are “perfectly fine trees”; they’re not old or unwell, Ethington said. And the beetles are wiping them out.
“What we’ve got going in the San Juan Forest is not a natural circumstance. It’s definitely an outbreak, most likely caused by a combination of forest composition and climactic factors,” Ethington said.
Climate change most likely plays into what’s happening. So does forest composition: The beetles thrive in monocultures, or masses of a single species, which much of the forest is around here.
“It’s even aged, and it’s all ponderosa pine. When you have a single aged, and single species monoculture, these beetles are just going to go crazy,” said Kyle Personett, a forester at the Forest Service.
The roundheaded beetle is specifically concerning, as its behavior has progressively become more aggressive, Ethington said.
The Forest Service has known about the roundheaded beetle for over a century, but it has only ever killed trees farther south, mostly in New Mexico.
“Its distribution is changing a bit. It’s never been as far north as the Uncompahgre that we know of,” said Ethington. “It’s definitely spreading farther north.”
The outbreaks have never lasted so long, either.
In New Mexico, there were periodic outbreaks of the roundheaded beetle where it killed a lot of trees every three years or so, Ethington said.
“But then three years later, it’s gone. Whereas this outbreak has been going since 2013, and it just keeps on going,” Ethington said.
The three beetles of concern in our region have one year life cycles, which means they typically kill trees within a single year.
They target older trees, bore in and lay eggs. To try and prevent this from happening, trees have natural defenses: They push out resin.
“If they have enough resources – mostly it’s water availability – they can pitch out the beetles and stay alive,” Personett said.
The resin the tree pushes out settles into pitch tubes, a sure sign of a beetle-infected tree.
“We call them zombie trees,” said Personett. “They’re green needle trees but have a bunch of pitch tubes on them.”
Ideally, the beetles die in the sap.
But the 20-year drought in the area renders this defense practically useless. Plus, the different beetles fly at different times of year.
A tree might push out all its resin in early summer when the mountain pine and southwestern pine beetles fly. And so, when the roundheaded beetle flies in the fall, trees are defenseless.
“That’s what’s really creating this high mortality. You’re having a tree that was able to pitch out – you know, if you had a good winter – it can pitch out beetles in early summer. But if you don’t have a good monsoon season, in the fall, the roundheaded is coming in,” Personett said.
Once beetles successfully bore, they lay eggs. Eventually, the larvae eat their way around the tree’s phloem, which transports nutrients from the leaves to its roots.
Larvae eating their way around the entire phloem is what ultimately kills the tree. It’s called girdling the tree, and when a tree is girdled, it no longer can transport nutrients, Personett said.
“Imagine poking a hole in your lungs, and not being able to get air down there,” Personett said.
To be habitable, a tree has to be 6 or 8 inches around, which is why the beetles prefer older, more developed trees. These beetles are unable to complete their life cycles in small trees.
To the beetles’ benefit, the trees in our forests are all older and habitable. This area was once the largest timber producing forest in the state, so a lot of it was clear cut in the early 1900s.
That’s why most of these trees are the same age, between 90 and 100 years old.
Ethington and Personett said there are short-term and long-term solutions to try and bar the beetles from taking over more trees and ultimately changing the ecosystem to Gambel oak.
Short term, the Forest Service is undergoing sanitation, which is cutting down the trees with a lot of beetles in them, Ethington said.
Looking long term, the goal is to reduce the number of trees in the forest so each remaining tree has more water and nutrients to defend itself. That way, when the beetles fly, their resin defense mechanism can work properly.
“In the long term, it’s always going to be about the trees being more able to defend themselves,” Ethington said.
Because the beetles will always be there.
“They’re even there in Boggy Draw right now, they’re just not causing widespread mortality yet,” Ethington said.
“There’s no silver bullet in forestry or forest entomology. So what we can do is do our best to reduce beetle populations and to help trees be more well defended in the future.”
Community members interested in learning more about the beetle outbreak are invited to go on a field trip with the Forest Service on Oct. 1 to see what’s happening in the Glade. At 11 a.m. that day, participants will meet at Butler Corner and go from there.
To RSVP, email Kyle Personett at kyle.personett@usda.gov.
