This is the second installment of Mongabay’s coverage of active management tools for forest fires. Read Part 1.
Photographs of forests in the western U.S. from the mid-1800s show a starkly different reality compared to what we see today, says Paul Hessburg, an ecologist and professor at the University of Washington.
“It looks nothing like the current landscape,” he tells Mongabay.
Today, many of these forests are overgrown and dominated by younger trees. Back then, they were typically more open — “park-like,” according to many scientists. They were part of a broader mosaic: conifer-dominated forests mixed with deciduous woodlands, open meadows and wetlands in a patchy broth of diverse habitats.
Fire played an integral role — perhaps the integral role — in shaping these ecosystems. But soon, European-descended emigrants to the West shut it down in just about every way they could, with little understanding of the implications.
Hessburg and other researchers spend their careers teasing apart these dynamics and looking for ways to replicate those effects through a set of “active management” tools, such as prescribed burning and thinning. Where possible, the goal is often to usher fire back into the landscape at lower intensities to promote regeneration and avoid the catastrophic megafires that have destroyed communities in recent years.
In those cases, “The next fire often erases the opportunity for a future forest,” Hessburg says. “It’s so intense that it sterilizes soil [with] such burn severity, and it removes seed sources.”
But this embrace of active management isn’t universal. In a debate that has spanned decades, a group of scientists has opposed the broad application of these tools. While these researchers say the limited use of such tools might be called for in specific circumstances, they worry that a focus on them as the singular solution to the western U.S.’s growing fire problem will lead to misuse. And they argue that heavy-handed interventionism in forests could destabilize their long-honed ability to renew themselves.
“It’s not like we’re opposed to all kinds of active management,” says Dominick DellaSala, formerly chief scientist of the Wild Heritage Project at the Earth Island Institute, a California-based nonprofit. Instead, the message to active management proponents is “you’re not defining this well, you’re overhyping it, and you’re using the same tools … that have caused the damage that you’re trying to address.”
DellaSala, now with the Oregon-based Conservation Biology Institute, says active management is being “oversold,” and that its effects are limited by current conditions.
“These megafires are driven by extreme heat, drought [and] high winds caused by anthropogenic climate change,” DellaSala adds.
Instead of spending money and effort managing the backcountry, DellaSala says, we’d be better off concentrating efforts closer to home, judiciously using tools like thinning and burning to protect communities built close to forests.
The split has led to diverging streams of research, often with conflicting conclusions about the best course of action in confronting a rapidly changing world. Beyond the literature, some researchers and conservation organizations have taken the fight to the courts.
At its heart, the divide centers on questions about the role humans should play, particularly in the remaining areas of intact wilderness.
A history of suppression
In the not-so-distant past, fire was a frequent visitor to dry forests in the American West. It swept regularly through forests dominated by ponderosa pine (Pinus ponderosa) at least a few times per century, and in many cases more often than that, according to studies looking at the rings of thick-barked, fire-adapted species like ponderosa, Jeffrey pines (P. jeffreyi), and even the world’s most massive tree, the giant sequoia (Sequoiadendron giganteum).
“Each 2,000-year-old sequoia has experienced hundreds of wildfires in its lifetime,” says Bryant Nagelson, a research associate at the University of Nevada, Reno.
Whether caused by lightning or set by humans, fires balanced these systems amid their consistent dynamism, clearing away the overgrown understory and fallen trees, sparking a continual process of renewal, as destructive as it might seem to the human eye. These cycles also helped limit the number of trees drawing on the precious and often scant water available in dry forests.
A study in the journal Ecology and Society found that until the late 1700s, between 35 million and 86 million hectares (86 million and 213 million acres) burned every year in the contiguous United States. That’s about half the size of Alaska. By the time the study was published in 1998, fires were burning no more than 7 million hectares (about 17.3 million acres) annually, consuming just a fraction of the leftover biomass they had before.
These past, repeated fires reduced the amount of “fuel” left behind, lowering the intensity and destructiveness of subsequent fires, Hessburg says, adding that Native Americans understood those dynamics.
“The most important process … is fire for keeping fuel loads low,” he adds in a follow-up email. “Our Indigenous people knew that for 10,000 years or more in the West, and that’s why they burned so bloody much, to obtain the food and resources they needed to live and to keep the woods open so they didn’t die on a landscape that could otherwise kill them.”
But after U.S. expansionism displaced Native American tribes, Hessburg says, the new settlers on the landscape didn’t learn from their predecessors.
“We foolishly are hands-off, rather than burning them and maintaining them,” he says.
A February 2025 study led by Sean Parks, a research ecologist with the U.S. Forest Service, in the journal Nature Communications using tree ring data found an ongoing “fire deficit” in dry western forests currently. The authors report that even in a record-breaking year like 2020, substantially smaller proportions burned than had occurred prior to the mid-18th century.
By pulling back and not using the tools of active management, Hessburg says we continue to repeat the same mistakes.
For example, research reveals that wildfires killed 13-19% of mature giant sequoias in their native range in the late 2010s and early 2020s. But around the same time, groups opposed to thinning and prescribed burning had filed a lawsuit to stop active management in Sequoia and Kings Canyon National Parks, both home to sizable sequoia groves. The effort failed, paving the way for continued work that proponents say is vital to the survival of the iconic species.
No ‘one size fits all’
Part of the disagreement over active management stems from fundamentally divergent views on how forests looked before fire suppression in the West. Proponents of active management often describe these historical forests as more open, with fewer young trees and less brush clogging the understory. But skeptics raise concerns about an obsessive focus on transforming all of today’s forests to the park-like paradigm.
“Many forests aren’t supposed to be thin,” says Diana Six, a forest entomologist and professor at the University of Montana, who has co-authored several papers with DellaSala. “They function best if left alone. That’s why there are still these few remnants that are functional.”
Often, skeptics argue for limiting — or outright halting — active management in the last remaining old-growth stands that have been minimally affected by logging and exploitation. In a recent study published in the journal Biological Conservation, Six, DellaSala and their colleagues highlight the damage to these ecosystems that can result from thinning, such as the compaction of soil and the construction of roads for large machinery. Those roads, in turn, often provide easier access to the backcountry for humans, who are responsible for more than 80% of all wildfires in the U.S., according to a 2017 study.
With some forms of active management, “You’ve lost a lot of the soil microbial communities, the fungal interactions — all the things that keep those forests super functional,” Six says. “When you disrupt forests, you break that stuff down, and they aren’t as resilient.”
She and her colleagues also caution that more open forests are drier and thus more prone to fire due to less overstory to trap humidity.
Six compares the bark beetles that are a major focus of her work to fire. Beetles and fire have both typically been seen as forces to be stopped “at all costs,” she says.
Bark beetles can kill trees by the hundreds, particularly those that are stressed by drought, a condition exacerbated by higher climate change-driven temperatures and by high densities of trees on the landscape drawing on dwindling groundwater. Research suggests that thinning stands can reduce the number of trees that die, and it may reduce the fuel available for future fires, though the interactions are complex.
Six and her colleagues warn that thinning in response to these outbreaks can take healthy trees along with those affected by beetles.
“When we tried to stop fire, how good was that for the forest? Not very,” she says. “Bark beetles are natural disturbance agents that have shaped our forest just as much as fire. And if we take them out, it’s every bit as bad as fire suppression.”
Beetles also introduce unique dynamics into the functioning of forests.
“We’ve done some studies looking at beetle-killed forests, and there’s usually 5, 10, 20% of these big, mature trees that survive,” Six says. “They’re genetically different, and they’re not even being attacked.”
Those findings highlight a problem with intervention, she adds: Removing resistant trees means that their genes won’t filter down to the next generation, potentially setting up even greater vulnerabilities later on.
“I’m not anti-management completely, but it should be more ecologically appropriate,” Six says.
Many pro-active management scientists agree with that contention.
“Is there a one-size-fits-all? No, that’s a terrible premise,” Hessburg tells Mongabay. “Geography matters. Forest conditions matter.”
But as he sees it, active management still has a role to play.
“Fire and bark beetle outbreaks are both natural processes,” Hessburg adds, “but they’re natural processes now in an unnatural role” because of how humans have altered forests with fire exclusion, logging, and now climate change.
Proponents of active management also agree that there are places where a hands-off approach makes sense — but context is critical.
“Yes, it probably makes sense to exempt old growth stands in areas that historically experienced very infrequent fire,” such as the rainforests of the Pacific Northwest, the Forest Service’s Sean Parks tells Mongabay in an email. Where fire was more common, however, active management is the way to go, he adds.
‘Legacy of mistrust’
Hessburg and others see the rejection of active management in part as a response to the “legacy” of commercial, industrial-scale logging of natural forests. Those rampant harvests often took the oldest and largest trees in the U.S., before a mix of science, policy and advocacy for species like the northern spotted owl (Strix occidentalis caurina) caused a shift away from the practice in the 1990s.
“There’s mistrust in the tools because they were used badly for half a century,” Hessburg says.
“We liquidated 90% of the large old trees and forest patches of old growth, and it takes centuries for that stuff to grow back again,” he adds. “That was a depredation on ecological systems. It’s a real thing.”
However, Hessburg and other researchers say active management skeptics have a tendency to conflate thinning with full-scale commercial logging. He says logging can indeed be part of active management, often in an effort to recoup some of the high costs of thinning hard-to-reach forests. But he adds that best management practices call for leaving the largest, oldest trees standing and minimizing disruption of the soil.
Still, DellaSala and his colleagues say they worry the temptation to remove the most valuable trees will prove too great.
“That’s the nail on the head. Money grows on trees,” DellaSala says. “That’s what they’re going to gravitate towards … and that’s when we get into trouble.”
He and his colleagues also raise concerns about removing what wildfires leave behind. Often, big fires will leave the charred cadavers of dead trees. Some trees even remain standing, bristling like a pincushion on scorched hillsides. Others fall to the ground, where they could fuel future fires.
Removing those trees could affect other species, however, Six says.
“Dead wood is the life of the forest. There’s more life in the dead stuff than in the living stuff,” she adds. “It supports everything from nutrient cycling … to fungi to microbial communities to birds to mammals to the way the forest regenerates.”
Interpreting the data
Undergirding disagreements over whether to intervene or leave forests largely alone are fundamental differences in the data and how they’re interpreted. They disagree over the historical severity of fires, for example. Many researchers like Hessburg generally contend that most fires in dry forests over the millennia were mostly limited in their intensity.
But scientists like DellaSala argue that high-severity fires were more common than pro-active management researchers acknowledge. That conclusion undercuts one of the primary justifications of active management — that it modulates fire intensities to more manageable levels that, in turn, benefit the forest as a whole. Active management skeptics even say that high-severity fires might actually create the habitats that some species prefer, with some research lending support to that conclusion for a member of the weasel family called the Pacific fisher (Pekania pennanti).
At the same time, however, other research suggests that fishers could lose almost all of their habitat by the end of the century without the application of active management.
“I think done right, with the intentions of keeping the large, mature, fire-resilient trees [and] fire-resistant trees, it’s probably warranted in some of these areas, just to actually conserve the biodiversity,” Parks tells Mongabay in an interview. “These very species that make up the biodiversity component of these old-growth stands historically survived these somewhat frequent, low-severity events, or else you wouldn’t even have spotted owls, or Pacific fisher, or whatever critter you’re interested in.”
There’s a similar disconnect over carbon. DellaSala and Six say that active management reduces carbon stores and releases pulses of carbon into the atmosphere that might otherwise remain locked away, particularly when the tools are applied in wetter forests.
In dry forests where fire was historically a much larger part of the landscape, however, the way forward gets more complicated. Leave them alone, and the carbon stores will likely go up, at least initially, forest ecologist Matthew Hurteau acknowledges. But there are “tradeoffs”: Without thinning and prescribed burns, fuels accumulate, making extreme fires — and larger releases of carbon —more likely, he says.
In the 2000s and 2010s, Hurteau, a professor at the University of New Mexico, focused on modeling the effects of fire on forest carbon storage with an eye toward how to stabilize carbon stores over the long term.
More recently, he has grappled with the growing effects of climate change. In California’s Sierra Nevada Mountains, drier conditions, in tandem with bark beetle outbreaks, have killed even large trees. In one of Hurteau’s favorite study sites, Teakettle Experimental Forest, nearly a third of trees in a section where fire had been kept out died during a five-year drought from 2012-2016, potentially increasing the risk of severe fire.
Overall, the warming and drying trends have meant that these types of forests can now hold less carbon than they used to, Hurteau and his colleagues report in the journal Frontiers in Ecology and the Environment. Active management can help, they write, but those tools come with their own challenges, especially in a changing climate.
‘Unnatural role’
In My First Summer in the Sierra, naturalist John Muir wrote, “When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” Fire and forests seem particularly apt teachers of this lesson. We’ve pulled on those connections, shredded some, and tied others to each other in ways that didn’t exist before. Now, we’re left holding a clutch of those hitches and wondering what to do.
We do know that the “inevitable fire,” as Parks says, will continue to be a constant in these fluid landscapes, and how we prepare for it is perhaps the single most important question for the future of these forests.
To some, the answer lies within the forests themselves.
“If we think more … ecologically, we could see that forests are functional organisms and that doing these surgeries are not necessarily beneficial,” Six says. “So if we are going to go in and be that invasive, we should have a really good reason.”
To Hessburg and the scientists who agree with active management, that reason stems from the massive changes we’ve made to our environment.
“We created a climate that’s hostile to people and health and forests,” he says. What’s critical now is finding ways to adjust, for both ourselves and our forests. “Climate change is advancing very, very rapidly, so what the landscape looked like historically is not the future landscape that we have to adapt for.”
