Forests under siege
In Northern New Mexico, a growing list of pests are killing high-elevation trees already weakened by drought, climate change
On a Friday in February, John Formby drove up Hyde Park Road near Santa Fe for a hike with his dogs.
Rounding a curve about a mile before the Big Tesuque campground, Formby spotted a large swath of conifers with a red tinge: a sign the trees’ needles were dying.
“I felt there was just something unusual about it,” recalls Formby, an entomologist with New Mexico State Forestry and the person charged with heading the state’s forest health program.
The following day, he and two more insect scientists from the U.S. Forest Service hiked to the trees to investigate the cause of the needle kill.
What they found was an infestation of Janet’s looper caterpillar, the latest addition to a growing list of deadly enemies of Santa Fe National Forest.
Janet’s looper, which feeds on the needles of conifers, has been rarely identified in the wild and never this far north. For a bug guy like Formby, it was a major find.
“I’ve earned my keep,” he jokes.
But the discovery was bittersweet for Formby. It meant yet another pest is at work on high-elevation trees in Santa Fe National Forest, an area that already has suffered grievous insect damage. The forest’s high-elevation trees have been increasingly ravaged in recent years by bark beetles, and much more damage is predicted because of warming temperatures and less snowpack due to climate change.
From 2013-17, tree mortality caused by Douglasfir and spruce beetles was mapped on more than 133,000 acres of Santa Fe National Forest. Nearly half of the Pecos Wilderness has been hit by the beetles and other pests.
The news only gets worse: The U.S. Forest Service says nearly 300,000 more acres across the 1.6 million-acre forest are at risk of significant tree loss by 2027, and scientists at Los Alamos National Laboratory have said it is highly likely New Mexico will lose the vast majority of its forests by 2050.
In addition to Santa Fe National Forest, Carson National Forest is at high risk of massive tree mortality by 2027.
Teresa Seamster, chairwoman of the Northern New Mexico group of the Sierra Club’s Río Grande Chapter, says it is sort of like the forest is succumbing to an illness.
“The illness is the change: the heat and the lack of moisture,” Seamster says, adding it is hard to put the magnitude of the loss into words.
The tree kill isn’t just changing the aesthetic of the forest. Downed trees and standing dead ones are making it more difficult and more dangerous for hikers, hunters and others to use the forest. Ecosystems are changing. Plants and wildlife are being affected.
Mountainsides of red, then gray
The troubling tree mortality in Santa Fe National Forest is part of a much larger picture.
From 2000-17, bark beetles killed trees on 55.6 million acres across the West, according to the U.S. Forest Service. Lower-elevation trees, such as ponderosa pine and piñon have been hit, along with conifers in high elevations.
Whole mountainsides in Colorado have turned red, then gray in recent years from dying trees.
“That is comparable to what could potentially happen here,” says Dennis Carril, fuels program manager for Santa Fe National Forest.
Lack of moisture stresses trees and makes them more susceptible to pests. Warmer winter temperatures allow pests to persist year-round.
“Widespread tree death and fires, which already have caused billions of dollars in economic loss, are projected to increase, forcing wholesale changes to forest types, landscapes, and the communities that depend on them,” according to the U.S. Global Change Research Program, an initiative created by Congress.
The massive die-off of trees in the West also has implications for climate change. Live trees absorb carbon dioxide, the primary cause of climate change, through photosynthesis. It’s then turned into biomass. In death, they release carbon.
There is good and bad news when it comes to fire danger from the tree mortality at the high elevations of Santa Fe National Forest.
The tree loss won’t increase the threat of fire, Carril says. “Typically, high elevation is not available to burn when we have a snowpack that is average or better,” he says.
The problem is that warming temperatures are reducing snowpack. And when there is no snowpack, anything up high — regardless of whether it’s dead or alive — can burn, he says.
Moving north
An aerial survey in the spring identified nearly 10,000 acres under attack by the Janet’s looper caterpillar.
In addition to the trees hit on an estimated 100 acres near Aspen Vista, trees in and near the Pecos Wilderness, in the Santa Fe River watershed and in or near the Gallinas River watershed have been infested.
Janet’s looper caterpillar is feeding mostly on Douglas fir and white fir, but the inchworm also is in other conifers, including an estimated 50 acres of bristlecone pine at nearly 11,000 feet on Elk Mountain.
It is the first time the looper has been found in bristlecone, the highest-elevation pine in New Mexico.
Janet’s looper caterpillar was first described about 50 years ago, and the first known outbreak in the Southwest was in Arizona in the 1990s. The only previous known outbreak in New Mexico was in 2005-06 in Lincoln National Forest in the southern part of the state.
The caterpillar feeds in the winter, and the number of acres impacted by the species is expected to grow before the population collapses.
The silk woven by the caterpillars throughout the bristlecones glistens in the morning sun. The insects use the silk to travel. When the wind hits the silk, the caterpillars are blown to other trees to continue their destruction. It’s called “ballooning.”
It takes just a few minutes for Formby to find one of the tiny caterpillars feeding on the needles of a bristlecone.
“We think with warming temperatures it is moving north,” he says.
Eventually, a virus or viruses in the soil will help kill the caterpillar. Extreme cold weather also could wipe out the inchworm. Most trees will recover from the defoliation; some won’t.
Formby estimates 10 percent to 30 percent of attacked trees will die. Some of the infested bristlecone pine on Elk Mountain are probably more than 200 years old, he says.
Other defoliators also have been at work in Santa Fe National Forest, including the western tent caterpillar, which has attacked aspen, and the western spruce budworm.
The western spruce budworm has done the most damage, defoliating trees across nearly 320,000 acres of the forest from 2013-17, according to aerial surveys.
The bug kills only a small percentage of trees, but repeated defoliation can hamper tree regeneration.
Targeting the big trees
Bark beetles have been the main cause of tree death in Santa Fe National Forest, and most of that loss in recent years has been occurring at high elevations.
From 2013-17, tree mortality from the Douglas-fir beetle has been found on nearly 45,000 acres, according to aerial surveys. Tree death from the spruce beetle has been mapped on more than 88,000 acres.
Tree mortality from the Douglas-fir beetle is scattered across Santa Fe National Forest, according to the surveys. Increased beetle activity is found in healthy trees around burn scars.
The spruce beetle has hit the Pecos Wilderness especially hard, but tree death has also occurred in a large area between Pecos Baldy and Santa Fe Baldy in the Sangre de Cristo Mountains, as well as in a large pocket around Chicoma Peak in the Jemez Mountains. Aerial surveys last year also showed a small but growing area in the San Pedro Parks Wilderness northeast of Cuba.
“You’re got a massive, fairly fast-moving conversion of our forest to a different type of landscape,” the Sierra Club’s Seamster says.
“Having the forest here is just a huge part of this whole landscape, and without it, it’s going to be desolate,” she says. “And you almost don’t want to live to see that, but then you’re just copping out.”
As if all the other threats weren’t bad enough, Formby says Santa Fe National Forest is thick and prime for spruce beetle, which favors large, stressed trees.
“Anyplace where there’s a lot of spruce and the spruce is large and old, that is considered high risk for spruce beetle,” says Andrew Graves, an entomologist with the U.S. Forest Service.
On the positive side, Graves says, aspen and other new growth will eventually appear in areas of conifer mortality.
“The forests following insect outbreaks can be very resilient and respond very quickly to that change,” he says.