Drought, plague and fire: What one Colorado forest is up against
RIO GRANDE NATIONAL FOREST — The high alpine forests are a sickbed. Swathes of gray trees are bald on one side, with patches of russet needles fading into scraggly branches. Others show thick strips of bark sloughed off, revealing bleached trunks beneath.
Much of the 1.86 million acres of Rio Grande National Forest is dead. Close to half of that acreage is high-elevation spruce-fir forest, mixing into ponderosa, piñon and juniper at lower elevations, and turning to prairie on the valley floor.
“Much of the fir forest, the larger trees have experienced 95% mortality,” said Vincent Dupont, the acting vegetation program manager with the U.S. Forest Service. “What’s left are smaller trees, about 5 inches in diameter.”
The 2002 drought was a massive catalyst for pests, including the spruce beetle, which in Colorado impacted 1.89 million acres statewide over two decades. The beetles target larger Engelmann spruce trees, burrowing small holes under the bark to lay eggs. When the larvae hatch the following year, they feed on a tree’s vascular system.
They often move in a circular path, a behavior called girdling. That creates “a ring under the bark where the tree is cut off — no nutrients, no water — and kills off that part of the tree,” Dupont said.
Without rain, he said, trees are more vulnerable. They cannot produce resin, a sticky defense mechanism to protect themselves against the beetle larva.
Spruce beetles are not the only infestation. The mountain pine beetle decimated lodgepole pine populations and attacked ponderosas, too.
Historically, beetles and forests had a symbiotic stalemate, with a lower number of beetles clearing out sick or dying trees. But since the 2005 outbreaks, abundant beetle populations killed otherwise healthy, mature conifers. The combination of compounding bad drought years, coinciding with a larger number of beetles, means millions of acres of deadfall.
Dupont, who grew up in Antonito, Colorado, east of the Rio Grande National Forest, said the agency’s first priority is to remove dead trees from campgrounds and other areas where they pose a threat to human health.
“There’s no bringing those trees back,” Dupont said. “But I’m trying to clean up and get the forest restarted.”
The Forest Service is replanting Engelmann spruce. “Hopefully, we’ll give it a jumpstart,” he said. “It’ll never look like it did pre-beetle in our lifetime, but we’re trying to set it up for the future.”
From beetles to wildfire
With drought comes fire, and the San Luis Valley is not unscathed.
Since 2000, wildfires have burned nearly 300 square miles of the valley (an area the size of New York City). This included the West Fork Complex, where a series of wildfires sparked up and burned through 88,000 acres of beetle-stressed forests in 2013. In total, the multiple fires of West Fork consumed 179 square miles, mostly on public lands.
In June of 2018, the Spring Fire erupted near Fort Garland, and ripped through 108,000 acres. In that fire, Costilla County lost 62 homes, which is 6% of residences in the county. These fires were the second and third largest in Colorado history, until massive blazes in 2020 pushed them down the list.
Robert Andrus, a forest ecologist at Washington State University, studied forest relationships with both bark beetle and fire for years in Colorado. Fires are reshaping Colorado’s forests, he said, showing research that seedlings are struggling to survive in burn scars, often because of higher temperatures. Downed trees mean a loss of shade, and so charred areas absorb more sunlight.
After devastating burns, ponderosa and Douglas fir forests are converting to grass and shrubland after fires. The drying and warming climate mean fewer seedlings can establish themselves, a 2020 Colorado State University study found.
In contrast, beetle-bitten forests, despite their high mortality, may recover — but it may take over a century.
“We generally saw really high abundances of seedlings and saplings of smaller trees,” Andrus said, “as well as some surviving overstory trees, suggesting that those areas are going to return to forest.”
Still, there’s no certainty for recovery on an ever-hotter globe, even in places where the damage isn’t so striking.
“Oftentimes, fire and bark beetle outbreaks are the most visually obvious to people, and they can see those changes to the forest,” Andrus said. “But forests that aren’t affected by those disturbances are also experiencing higher rates of tree mortality as a result of the warming climate.”
This project was funded by a grant from the Water Desk and by States Newsroom, a network of nonprofit news organizations and home to Source NM.