How Wildfire is Erasing the Forests of the American West

One summer evening in 1996, an abandoned campfire caught the woods of the Jemez Mountains in northern New Mexico on fire. The next day, the wildfire exploded.

The fire trapped 48 firefighters on a dirt road, forcing them to deploy their shelters, and flames advanced on the Los Alamos National Laboratory. Ultimately the fire consumed an engine and burned the arms of a firefighter who'd lost his gloves—but it did not reach the lab.

What surprised everyone in the aftermath was the number of dead trees.

The Dome Fire burned at such an intensity across 6,664 acres, some 40 percent of its total path, that it killed swaths of mixed conifers and ponderosa pines that had survived centuries of fires. But this fire was hotter than the others.

People said the trees would come back, no big deal; and indeed they started to. Then in 2000, a larger fire, the Cerro Grande, ripped through the scar of the Dome Fire. Then in 2011, a much larger fire, the Las Conchas, ripped through the scars of both fires.

Now 30 years have passed since the Dome Fire, but the trees have not come back.

Ridgelines of the Jemez Mountains, once cloaked in green canopies, are now craggy, barren, and brown. An emerging body of research is showing that those early fires, once novelties across the West, have become the norm. According to a paper published in late June in the Proceedings of the National Academy of Sciences, forest-eliminating wildfires are now the most common type of fire in California.

Research published in the past few years suggests much of the West is following the same trend. In the last four decades, largely because of wildfires, nine percent of forests across the West have died.

While it is too soon to know the ecological fallout from the many fires burning this summer across the western U.S. research suggests that the damage may leave permanent scars. In the coming century, parts of the region will lose up to a third of its forests.

To look for clues to how this will happen, look to what’s unfolding in the Jemez Mountains, scientists say. And what’s happening there, they also say, is dire.

A New Type of Fire is Burning

Before we started putting them out in the 1880s, most of the wildfires out West were so-called "good" fires, crawling across the forest floor every two to 20 years, consuming logs and leaf litter and shrubs and grass. Fires maintained ecosystems.

Today they are just as likely to kill them. The high-severity fires seen more frequently today are the kinds of fires whose smoke crosses the continent to dim the sun in New York City. They dominate the land after 140 years of fire-suppression policies and practices have largely banished good fires. As the West continues to heat up and dry out, the nearly century-and-a-half of backlogged fuels in the forests are going up all at once.

"Basically, as long as you have a bunch of fuels, then the drier climate is going to give you bigger fires," said Park Williams, a geography professor at the University of California Los Angeles and an author on the recent PNAS paper. "It's easier to start fires, and it's easier to spread fires."

The Jemez Mountains are ground zero for this phenomenon, said Andreas Wion, the lead author on a paper, published today, examining how fire is reshaping the mountains. He notes that scientists have studied this landscape's fire history more than anywhere else in North America.

Wion, a post-doctoral researcher at the New Mexico Forest and Watershed Restoration Institute, compares the process unfolding in the Jemez—fire after fire consuming more and more of the forest—to a mouse eating cheese. Ultimately, his and his colleagues' research suggests, the mouse will likely eat the entire wedge.

By 2065, Wion predicts fewer than half of the conifer forests of the Jemez will remain.

By 2115, between five and 33 percent will remain. "We will likely not have forests to pass onto our next generation if everything keeps burning the way it is burning and you just let it burn," he said. "The forecasts are dire. It's just unsustainable."

Why Today’s Wildfires Burn Differently

Many of these wildfires have more in common with bombs than they do natural processes.

The kind of wildfire that most western forests evolved alongside spreads outward, its temperatures spiking highest along its leading edge as it consumes new fuels, stopping when it runs out of things to burn or is put out by rain, say, or the absence of wind.

But this more severe species of wildfire often sustains itself. Feeding on fuels stockpiled in the forest by a century of fire exclusion, the fire concentrates heat at its center, getting so hot it sometimes creates its own weather.

Pyrocumulonimbus clouds have been documented billowing 25,000 feet above these fires. These clouds—a type of mushroom cloud—release downdrafts that drive wind along the surface of the fire, blowing flames outward and killing everything in its path.

The spread of these fires is often described as an explosion. One such fire in the Sierra Nevada in 2020, the Creek Fire, grew by 637 percent on its second day. Scientists call the phenomenon a firestorm.

In 2022, six researchers demonstrated that firestorms are so unprecedented that conventional computer models don't predict their behavior. Others have found models designed for urban bombing campaigns do a better job.

There is historic precedent for wildfires behaving like bombs out West. The tops of mountains and their ridgelines, which hold onto snow into the summer, are often wet and resist fire. Thus a forest grows thicker and fuels amass on its floor.

While these high-elevation fires tend to kill the trees within their perimeter—or at least kill the tops of trees such as aspen, which resprout—they only blow through once every several hundred years. Forests at lower elevations on mountains or in valleys, or encircling a town, are adapted to lower-intensity fire that returns more frequently. These forests are where many of the hot fires are burning today.

"Fire—period—is not bad," said Ellis Margolis, a U.S. Geological Survey research ecologist in New Mexico. He is also a co-author on the Jemez paper. "It's the way that we've pushed it into this other form, which is probably unprecedented, that's bad."

Permanently Changing the West’s Forests

The size, frequency, and intensity of modern wildfires is transforming landscapes. Scientists have dubbed the process "type conversion."

A landscape ‘converts’ in a number of ways.

A forest might not grow back if fire incinerates large areas that contain species, such as ponderosa pines, that can’t cast cones far enough to reseed the blackened earth.

That mature forest might also be lost if a second fire, fueled by the dead trees left behind from the first fire, kills seedlings and consumes remaining seed on the forest floor. Seedlings can also fail to grow because without the shade from the canopies of mature trees, they can not survive in the West’s hotter and drier climate. Then, with the sun now beating on the forest floor, shrubs and grasses sprout and outcompete them.

Researchers are finding conversions can last centuries, near-permanently changing the behavior of fires to come.

Grasses, for instance, are finer fuels than trees and dry out quickly. They also store most of their biomass underground, a fire adaptation that allows them to resprout following a burn and then burn again the following season. While trees go up hot, grasses go fast. "Not only is grass a flashy fuel, it can be a continuous carpet of fuel," said Jennifer Balch, a geography professor at the University of Colorado Boulder. "It can carry fire very far and very fast."

Dangerous for Trees and People

As forests transform into grasses and shrubs, these new landscapes move wildfire more quickly across them.

In 2024, Balch co-published a paper in the journal Science that analyzed 60,000 fires that burned across the U.S. from 2001 to 2020. She and her colleagues found that the rate at which a fire could grow over the course of a single day had on average doubled in the West and quadrupled in California. News tends to break around a wildfire's size, but it's a fire's speed that threatens communities.

In 2018, the Camp Fire in California killed 85 people and destroyed 13,696 homes. It grew by some 52,000 acres on its first day.

In 2021, the Marshall Fire in Colorado, the state's most destructive fire to date, destroyed 1,084 homes. It traveled three miles in the first 60 minutes after it started, fanned by winds exceeding 100 miles an hour.

Grasslands, which had grown lush in the spring and dried out come summer, accelerated both conflagrations.

In the Jemez Mountains, Margolis and his colleagues know from their research that good fires used to burn through the forests every decade. Margolis thinks the fires used to spread in grasses because, after the transcontinental railroad opened the mountains to grazing in the late 1800s, livestock chewed the grass down to the dirt, and the fires ceased.

Then in the absence of fire, the forest grew thick, and the grasses, shaded out by the trees, did not come back. Now, as the grasses return, along with shrubs, it’s the trees that aren’t coming back.

"This is an emerging phenomenon," Margolis said, and there is a lot they don't yet understand. But their models are clear about one thing: the forests are receding.

Margolis, 52, has been working in the Jemez since 1999—half his life and no time at all for a mountain and its trees. Yet in his lifetime, he has watched shrubs and grasses come back to the east side of the mountain.

This time there are no more trees towering above. "Sadly," he said, "in my lifetime, these places won't regenerate as forests. They're converted. They're gone."