California’s Caldor Fire ripped its way across the Tahoe Basin this week, forcing thousands to evacuate, burning homes and communities in its path, and staining Lake Tahoe’s iconic blue waters with falling ash.
The fire, like many others burning across the U.S. West this year, spread rapidly in part because it’s burning intensely, propelled by hot, dry, windy weather conditions and forests overpacked with trees—food for hungry fire.
But it has also run up against some areas that have been “treated” to reduce their fire risk, patches of forest—some big, some not so big—that have been trimmed in the past, either by hand with chainsaws and masticators or with carefully managed prescribed fire. These treatments are intended to make forests healthier and more resilient to all kinds of pressures, including fire.
In the fires burning across California this year, and in other major recent fires, experts say these treatments may have done their job—which is not to stop the fires but to lower their intensity enough that they can be controlled.
The treatments serve many purposes, but one crucial role is that “they’re meant to give firefighters an opportunity to defend life and property,” says Kelly Martin, the former chief of fire for Yosemite National Park. “Now what we’re seeing is, we have several hundred-thousand-acre fires bearing down on these communities—for what it’s worth, they’ve done their job.”
The megafire era
Fires in the West are getting bigger and more intense. 2020 saw the country’s first “gigafire,” a burn that spanned more than a million acres, much of which burned at high severity—the kind of fire that generally causes great harm to homes and ecosystems alike.
The reasons for these changes are many. Crucially, the weather conditions that spur fast-spreading and intensely burning wildfires are becoming more common as climate change heats up and dries out many parts of the West. The fire season overall is lengthening, starting earlier in summer and stretching later into fall, so long that it’s essentially fire season year-round, a captain in California’s firefighting service has said. Dry air is becoming even drier; summer rainfall is sparser; nights are staying warmer, keeping fires active through times that used to provide a window in which to fight them; and the winds that fan the flames are as strong as ever during summer and fall, the riskiest times in much of the region.
At the same time, the West is facing a “fuels” overload. The region’s landscapes used to burn frequently; estimates suggest at least four million acres of California used to burn annually from a combination of fires set intentionally by Native Americans and natural lightning ignitions. Native American fire practitioners say that many areas burned every few years or sometimes even more often. In the northern Sierra Nevada, where the Caldor and Dixie Fires burn now, lower elevation forests probably burned every five to 30 years or so. But from the early 1900s until the late 1970s, federal policy dictated that any and all fires should be suppressed thoroughly and quickly; the “10 a.m. rule”—that any new fire needed to be out by 10 the following day—guided the U.S. Forest Service until 1978.
The results have been disastrous. Many forests are now wildly overgrown, jam-packed with small, sometimes unhealthy trees and shrubs that are ready to burn explosively if set alight—a reality that is all too familiar for many who’ve found themselves in the path of fast-moving, intense fires like the 2018 Camp Fire, the 2020 Creek Fire, or any number of others. The Caldor Fire is burning through patches of forest that haven’t felt flames since before 1940, a CALFIRE staffer told the San Francisco Chronicle, or maybe even longer.
“The average fuel load right now is probably something like 50 tons per acre. Under the old fire regime,” when Native people managed the land, “it was probably more like 7 tons per acre—an order of magnitude less than what it is now across large areas,” says Rob York, a forestry expert with the University of California, Berkeley.
Such fuel loads change the way fire behaves. Super-charged burns that get up into tree crowns can not only damage the trees but also help kick off embers that can fly miles ahead of the fire front, starting new blazes and driving quick expansion.
“If we’d done fuels treatments across the whole landscape, we wouldn’t be getting that,” York says.
Fuels treatments aren’t a panacea. Super hot fires or wind-driven spread can overwhelm even a treated area. But treatments—either mechanical thinning or prescribed fire, or ideally a combination—can help drop flame lengths and the “fireline intensity,” measures of how intensely a fire burns. In turn, that can help slow the pace of fire spread.
While we can’t change the weather patterns or climate pressures, York says, at least not in the short term, we can control the fuels. It’s possible to thin out the region’s overloaded landscapes, using chainsaws, masticators, and other tools to thin trees and lower-level brush, and setting carefully managed, low-intensity “good fire.” Research suggests that in overgrown areas, using both strategies may improve outcomes.
“We need more good fire on the landscape, which has been suppressed and persecuted,” says Martin.
Evidence from the fire lines
Last year, as the Creek Fire ripped through the Sierra Nevada toward the foothill community of Shaver Lake, forester Ryan Stewart was worried but also hopeful. He manages a 20,000-acre property owned by Southern California Edison, a power company, that partially rings the community. At the property, they had done extensive fuels and forest management for years, hoping to make the landscape fire-resilient, less overstuffed than the surrounding area.
An intense drought from 2012 to 2015 upped the stakes. Millions of trees across the Sierras had died, and across the state, most were still standing among the living forest, a vast reservoir of potential kindling. And in 2021, a hot, dry summer had primed all the vegetation—dead or living—to burn.
But Stewart had seen this exact scenario coming. In tandem with agencies like the Forest Service and CALFIRE, his company planned careful treatments across its property and adjacent areas—“tying in” to other efforts along roads and in strategic spots in the mountainous landscape—to thin out the extra fuels.
The power company had a thorough plan to treat most of its key areas by 2022. But in 2020, when they were only about halfway done, the Creek Fire appeared. Even so, when the flames hit those treated areas, “it really helped stop the fire and helped those firefighters keep it at bay,” says Stewart. The fire didn’t stop entirely. But its intensity dropped so much that it could be directed—and with enough time to buy CALFIRE about 24 hours to get in position in the safely cleared areas—to keep the fire from consuming the whole community of Shaver Lake.
Even “just a little bit of treatment went a long way,” says Stewart.
In Oregon’s Bootleg Fire, a conflagration that burned intensely over 400,000 acres earlier this summer, the path cut across Sycan Marsh, a 15,000-acre preserve managed by the Nature Conservancy. A good chunk of the preserve is home to dryland forest that used to feel fire about every 13 years on average, says Ryan Haugo, the director of conservation science for the organization’s Oregon chapter. But about a century of fire exclusion, plus logging practices that clear-cut and then replaced some areas with thickets of young trees all the same age and size, had left the forest thickly overgrown.
In the pre-fire suppression days, when Native communities used fire to manage the land, “there used to be 30 or 40 big trees per acre here,” says Haugo. Before the organization started its fuels treatment and ecological management efforts, in some of the previously logged areas there were probably hundreds.
But about 10 years ago, the group started muscling the forest back toward its long-distant shape, thinning it mechanically and with prescribed fire. It’s too early to say how all the treated areas dealt with the fire, but it certainly didn’t hurt. In one area Haugo visited post-burn, he saw one side of the road—untreated—burnt to a crisp, with “just a bunch of blackened sticks in the ground.” On another side, where they’d had a range of restoration treatments, large green trees still stood. “It almost looked like a controlled burn,” he says, the kind of good fire his group is hoping to restore.
Haugo cautions that other factors affect how a place burns besides the fuels treatment history. Some fires run so hot, or winds are so strong, that no treatments would mitigate them. In a burn engulfing hundreds of thousands of acres, even a big effort—Southern California Edison’s 20,000 acres at Shaver Lake—might not do much in the grand scheme of the fire.
But it can make a difference to a community in the fire’s way, or to firefighters trying desperately to get the fire under control. “These treatments are about forest health, and also about giving a tactical advantage to firefighters,” says Kate Wilkin, a fire ecologist at the San José State University. “In the area that has had treated fuels within the last five years or so, we expect the fire might still move through that area quickly but it won’t be climbing into the treetops, and would be the kind of fire a firefighter could control.”
Something similar might be playing out in the ongoing Caldor Fire. On the southeast edge of its footprint, a finger of unburned land stretches through the burn, an outline that neatly maps the edge of the Caples prescribed burn. The organization Sierra Forest Legacy spent years planning an 8,000-acre project to use fire to restore the area around the Caples Creek, finally initiating the burns in 2019 and treating about 3,000 acres with intentional fire that year. It’s not yet clear how the prescribed burn area affected the Caldor Fire’s behavior there, but Craig Thomas, the group’s former director who is now affiliated with the Fire Restoration Group, says it’s possible that these recent treatments made an impact.
Benefits from all sides
Decades of science have shown that fuels treatments change wildfire behavior. But the benefits go beyond that moment of crisis: They can also help forests recover afterward, and improve the overall health of the local ecological systems.
“What happens after the fire? One year, two years, three years? In areas that have been treated, you have trees surviving. You have a healthier forest. You have forests that don’t convert to shrublands, which is happening in parts of California that have burned very badly,” says Wilkin. Even the hydrology and biodiversity of the area can change for the better in areas that feel gentle fire rather than high-intensity burns characteristic of untreated zones.
Those benefits accrue when the burned zones get managed not just before the fire but after.
“The treatments can’t stop, because the forest keeps growing,” says Stewart. “You’re not just like, Oh, I’m going to treat this and you’re done—it’s got to be continuous. There’s a lot of planning that goes into that, but it can be done.”