Pests to blame for bare aspens
Western tent caterpillars are having good year, but that means bad news for fall foliage
Thanks to the voracious appetite of an inch-long, leaf-loving larva, fall colors in the Santa Fe National Forest are likely to be far less spectacular this year. In the early spring, the western tent caterpillar, a subspecies native to New Mexico and other western states, built its silken, webby, tent-shaped homes in the aspen stands along the Big Tesuque and Aspen Vista trails, both popular haunts for hikers hoping to take in the trees’ dramatic golden, shimmering leaves in the fall.
So far, the caterpillars have eaten their way through about half of the trees, leaving most of them leafless. As part of a cooperative agreement between Santa Fe National Forest and New Mexico State Forestry service, officials will conduct an aerial survey of the aspen stands next week to gain a better sense of how many acres have been impacted.
“It’s kind of shocking,” said Scott Canning, director of horticulture with the Santa Fe Botanical Garden. “People see it and think the trees are dead … but they’re not in most places. The tent caterpillar is not a good creature, but it is part of the habitat here.”
A drive into the mountains on N.M. 475 reveals a grim picture. Acres upon acres of aspens stand gray and naked, surrounded by so many deep green conifers and a stretch of still-green aspens higher up in the mountains. The trees are covered with dozens of silken tents, where the caterpillars make their homes. Smaller webby masses surround newly spun cocoons. Some late-metamorphosing caterpillars tread the branches. What few leaves remain are partially chewed and yellowing.
“It’s an unpleasant experience,” Canning said. “When they’re in numbers like this, they’re all over the trees, they’re all over the picnic tables. … When they’re feeding in the trees, you’ll hear their excrement. It sounds like it’s raining.”
After the caterpillars end their monthslong feast and build their cocoons, usually by midJuly, the trees will have a chance to regrow their foliage — but the new leaves will be smaller and fewer, and the fall colors less vibrant.
Canning described the caterpillar’s destruction as a “boom and bust cycle.” Every few years, a virus or fungus will kill off the population, allowing the trees to return to health again.
This is the sixth year in a row that the bugs have wreaked havoc in the aspen stands near Hyde Park Road. John Formby, manager of the state’s forest health program, said the outbreak “really took off with visually noticeable effects” in 2017, when 1,592 acres lost their leaves, and “it looks like this year will be worse.”
About 1,912 acres were defoliated in 2015, the most this decade, according to data provided by the U.S. Forest Service.
If the trend continues, officials said, trees could start dying.
Drought hasn’t helped. Stressed trees are more susceptible to pest invasions.
Still, Andrew Graves, a forest entomologist with the U.S. Forest Service, said he’s “not overly concerned.”
“Aspen is great at regenerating,” he said. “… I think right now we’re kind of on a wait-and-see mode. This drought, with this recent odd rain that we got and then with the timing of the monsoon, a lot could affect it.”
Formby said this fall’s view from Aspen Vista Trail might look similar to last year’s – some bronze-colored leaves will flicker in the wind, but most of the trees will appear bare.
Federal officials don’t keep numbers on how many visitors stream to the forest to take in the fall colors, but Bruce Hill, a forest spokesman, called the influx an “international event.”
“I don’t want to discourage the public from coming,” he said. “There are going to be wonderful fall colors to see despite what’s going on with the tent caterpillar.”
Property owners who notice the species’ distinctive tents on their own aspens can knock the nests out of the trees and stomp on them.
An all-natural pesticide, B.T., also is effective, Canning said. Spraying it introduces a stomachdestroying bacteria into the caterpillars’ systems, thereby dissuading them from eating the leaves. B.T. is harmful, though, to less destructive caterpillar species.