American Scientist

Stand at Glacier Point and you’ll instantly understand why it is one of North America’s iconic overlooks. The great trough of Yosemite Valley in California fills the foreground below and, with almost gravitational pull, carries the eye eastward to the crest line of the Sierra Nevada mountains. With its sheer granite walls, waterfalls that plunge hundreds of meters, and uniquely sculpted stone monoliths (such as El Capitan and Half Dome), words such as monumental hardly do justice to the scene.

It’s a landscape shaped by Pleistocene ice that widened and deepened valleys, rounded exposed granite, cached boulders and soils, and scoured routes for runoff that eventually became rivers and waterfalls. Even today, its groves of sequoia, a charismatic megaflora, inhabit sites where the ice failed to enter.

Pivot south, however, and you’ll see a scene as aesthetically bland as Yosemite Valley is gripping. The eye passes over it as fast as a stone skimming across a lake. The Illilouette Creek Basin is broad and rumpled, its granite surface camouflaged by forest, lacking the bold monoliths that make Yosemite Valley instantly recognizable. In the Illilouette, every iconic feature in Yosemite Valley has seemingly been inverted.

Yet a century after Yosemite National Park was first established, the Illilouette became a serious focus for management. The reason? It is a landscape informed by fire as fully as the Yosemite Valley was by ice, and, equally, its rock-exposed perimeter tends to contain fire within it, rendering it a kind of fire island. In 1972, those properties inspired a bold experiment to restore natural fire in the Illilouette. This effort involved ending the suppression of fires kindled by lightning strikes and allowing them to burn freely (under the right conditions). Amid national enthusiasm for all things wild, and in a place chartered to preserve the natural scenery “unimpaired” for future generations, reinstating a natural process seemed an obvious thing to do. At that time, the fire community of fire officers, administrators, and researchers regarded the nation’s public lands as headed toward an impending disaster. Thanks to land use, including the practice of fire exclusion, wildlands were reorganizing in ways that built up combustible vegetation to dangerous levels and allowed ecological dry rot to damage fire-impoverished landscapes. The Illilouette experiment was an attempt to let nature recover, using nature’s own means.

Over the next 50 years, the horizon of that project lengthened beyond the granitic rim of the Illilouette. What started as a crisis visible in public wildlands metastasized into a generally acknowledged planetary calamity. The Pleistocene has evolved into a Pyrocene. Everywhere, fire is replacing ice. Uncontrollable wildfires ramble across open lands; untamed fires transform biomes from peat and forest into plantations and pastures; and fires encased by machines bloat the atmosphere with greenhouse gases, acidify the oceans, and enable a global wave of extinction. Even the cars, buses, and asphalt that traditionally defined Yosemite’s management obsessions are possible only because of humanity’s combustion habits. In the Pyrocene, every defining trait of an ice age has seemingly been inverted into a fiery equivalent.

Reforming the Landscape

Yosemite is special. In 1864, amid the bitter Civil War, the U.S. Congress set aside Yosemite Valley and the Mariposa Grove of giant sequoias, ceding management to the state of California. At the time, the Miwok Indigenous people annually burned both the valley and the grove to facilitate access and hunting and to prevent bad fires. Between fires caused by lightning strikes and by travelers burning along trails (to keep paths clear and assist hunting), the backcountry burned as well. Smoke was constant and, according to early observers, scorch marks were visible on nearly every tree.

From the beginning, Yosemite’s fires provoked controversy. Authorities denounced fire as environmentally damaging; a kind of vandalism; an emblem of unenlightened primitivism; and messy—an index of social disorder. These were views commonly held by Europe’s elites, and accepted as axiomatic by foresters. They applied as much to Europe’s traditional fire users (and settler newcomers) as they did to Indigenous peoples in colonies from California to India and Australia. The United States’ first professional forester, Bernhard Fernow, dismissed the causes behind the country’s simmering landscapes as “bad habits and loose morals.” Western Australia’s conservator of forests, Stephen Kessell, grumbled that “only a few years ago the general public felt no compunction about setting the wild and untended forest alight whenever opportunity presented itself.”

From the beginning, Yosemite’s fires provoked controversy. Authorities denounced fire as a kind of vandalism, an emblem of unenlightened primitivism, and an index of social disorder.

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Nearly everywhere that European-inspired modernity went, it found landscapes routinely ablaze, and everywhere authorities made fire’s suppression a foundational doctrine of conservation. Yosemite’s Board of Commissioners applauded Galen Clark, the first guardian of the Yosemite Grant, for shielding the park from wanton fire. Park commissioner Frederick Law Olmsted, famous for designing Central Park in New York City, denounced “Indians and others” (primarily shepherds) for their promiscuous burning. Even John Muir, the genius loci of Yosemite and one of the era’s great observers of nature, wrote in 1876 that fire “is the arch destroyer of our forests, and sequoia forests suffer most of all.”

But almost immediately, the abolition of fire caused problems. Without routine flushing by flames, young trees filled up both the Yosemite Valley and the Mariposa Grove. Within a handful of years, it became difficult to view the granite walls and towering waterfalls that brought tourists to the valley, while white fir and incense cedar crowded around and obscured the giant sequoias. Worse, combined with windfall, those young woods threatened the giants with wildfire. To those who already distrusted fire, that enhanced threat argued for yet more protection against fire, which set up a cycle of well-intentioned but self-defeating policies. In 1889, wildfire did enter the grove. The failure to halt the flames, combined with other concerns, led Congress to return Yosemite to federal control the next year.

Not all of Yosemite’s commissioners had objected to fire. William H. Mills, for example, loudly proclaimed that he had “always respected the ability of the Indians to manage that valley” and that he regarded fire “as a very good method of management.” The removal of fire had only catalyzed unwelcome change. Such views were prominent among people who actually lived on the land, as well as several other commissioners and observers. However, the official policy (promulgated by the U.S. Department of the Interior) made fire-starting illegal.

The federal government sent in the U.S. Army to establish firmer control of the forest. Every summer from 1890 to 1914, a cavalry detachment bivouacked outside the Mariposa Grove, and later Yosemite Valley, enforcing rules against trespassing, timber theft, and fires. The army soon appreciated both the extent of burning and its value, and many officers argued for a program of regular burning. Captain G. H. G. Gale noted as “a well-known fact that the Indians burned the forest annually” and then concluded that the “absolute prevention of fires in these mountains will eventually lead to disastrous results.”

Nearly everyone in the mountains agreed, except officials. What became known as the “light burning” controversy bubbled up in California during the first two decades of the 20th century. Light burners referred to those who argued that the United States should emulate its Indigenous peoples and routinely burn forests, instead of conforming to European forestry. Foresters saw this movement as a challenge not only to their competence as firefighters but to their credibility and legitimacy as agents of conservation. U.S. Forest Service Chief William Greeley dismissed light burning as, in his words, “Paiute forestry”—referring to the burning practices of Indigenous Paiute peoples. In 1923, a commission convened by California’s Board of Forestry ruled against light burning, and the practice became anathema. Fire policy remained unchanged.

Restoring Fire

The same controversy bubbled up wherever modernity met traditional societies. The same discussion occurred in British India in the 1870s under the rubric of “fire conservancy,” with similar splits between those in authority and those charged with executing policy on the ground. Eventually, British foresters had to compromise in practice, though never in principle, and French foresters did the same (by looking the other way). Those in power would never formally acknowledge burning as legitimate land use because it defied the science of the day and bore a stigma of primitivism. Besides, fire was too useful as an emblem of wrecked lands. (It still is: Think of how fire is used today to symbolize the climate crisis.) The public, they argued, would be confused if asked to distinguish between long-standing burning practices and the ruinous burns that feasted on the offal of logging and land-clearing.

Half a century later, Yosemite forester Emil Ernst noted that: “Up until about 1906 this policy of fire suppression was openly and actively condemned by the highest responsible officials who, however, disregarded their own opinions and carried out the fire suppression and fire prevention policies with which they heartily and honestly disagreed.” That intellectual dissonance became institutionalized. In reality, the authorities had it backward. The real menace was mindless firefighting, not fire-lighting.

In 1930, the administrators of Yosemite National Park erected a lookout and a guard station, and began keeping formal records of fires. In 1933, the park was granted the money and muscle it needed to enforce the fire exclusion edict with the arrival of the New Deal, emergency conservation programs, and the Civilian Conservation Corps. Bolstered by that same largesse, the Forest Service announced in 1935 a universal mandate to control every fire by 10 a.m. the next morning. As an administrative edict, it was brilliant—unambiguous, quantitative, dramatic. As a guide to ecosystem health and fire protection, it was hopelessly flawed. It was a policy for cities, not the countryside.

Between 1962 and 1978, a reformation in fire thinking overturned previous doctrine. A new generation saw the same evidence differently, and a gestalt-like switch took place in which what earlier generations had seen as a boisterous forest of the future now looked like dysfunctional woods ready to explode in flame. In 1963, a commission chaired by wildlife professor A. Starker Leopold urged the National Park Service to actively manage its natural estate and cited the overgrown dog-hair thickets of the Sierra parks as a poster child for the need to restore fire.

At the same time, research was progressing on the western slopes of the Sierra Nevada at Redwood Mountain, the world’s largest sequoia grove. Most of the site lay along the western boundary of Sequoia and Kings Canyon National Parks, but the University of California, Berkeley, held part as an experimental forest, and under the charismatic leadership of fire scientist Harold Biswell conducted research on the dual threats posed by fire exclusion: Thanks to encroaching woods, wildfire could reach into the crowns of even giants, and the absence of surface fire (which could purge competitors) limited sequoia regeneration. The grove needed fire.

Research plots were soon matched with demonstration plots for showing how to recover that lost fire. Most of the park fire staff for Sequoia, Kings Canyon, and Yosemite National Parks learned their skills on the slopes of Redwood Mountain and studied under Biswell or his colleague Leopold. In 1968, the National Park Service replaced the 10 a.m. edict with a policy of fire restoration. Ten years later, the U.S. Forest Service followed suit. Deliberate, prescribed burning was one solution; another was to allow natural fire more room to roam. In 1972, Yosemite designated the Illilouette watershed for an experiment in fire restoration. The Illilouette provided proof-of-concept that became particularly important after the 1984 California Wilderness Act put 95 percent of the park into legal wilderness.

A basin emptied of flame began, patch by patch, to fill up with it. Fire returned as lightning strikes set fuels ablaze (any human ignition was suppressed), some burning new places, some reburning previous burn scars as they rejuvenated. Paradoxically, wilderness status complicated the restoration: It was acceptable to put out fires but not to light them, which meant a steady decay in the total area burned. Moreover, as bad fires worsened in California, it could be awkward to justify keeping Yosemite alight with good fires or to demand that its in-house fire crew tend its home fires rather than rally to the megafires that threatened surrounding lands.

Managing Fire in an Age of Gigafires

In retrospect, Yosemite’s experiment in fire restoration occurred at a benign time. When the Starr King Fire burned almost 1,500 hectares in the Illilouette in 1974, it seemed huge; 20 years later, you needed 10,000 hectares to shock; and 40 years later, 100,000. The term megafire was coined after the 2002 season; by 2019, gigafire had entered the fire community’s lexicon. Legacy fuels were mating with the climate crisis and, as more fires threatened communities and saturated California’s skies with smoke palls, it became harder to muster both the resources and the will to manage—rather than simply suppress—outbreaks, however much those massive firefighting endeavors failed and added to the problem.

The effort to restore fire was a revolution from the top that struggled to express itself on the ground. Policy could pivot quickly; practice could not. Most parks and national forests did not make the transition. Rather than being two sides of the same fire-management coin, firefighting and fire-lighting often became rivals. At Yosemite, the two groups had separate programs in separate administrative bunkers. Fire suppression had tradition, equipment, crews, and plenty of money. Fire management, which embraced a pluralism of fire practices, had an office in the attic (literally) of the administrative building, few resources, and scant funding. A failure to control a wildfire would prompt more effort to control it. A failure to control a prescribed fire could end a career. However natural its ignition source, however squarely embedded in legal wilderness, liability resides in the person or agency who decides to monitor, loose-herd, or generally manage fire rather than extinguish it immediately.

The checklists of decision points that govern whether to allow a natural fire to proceed swell with each year, with every new social value identified, with every glitch and stumble in fire practice, and with every personnel transfer into and out of Yosemite. Fire management must cope with the Clean Water and Clean Air Acts, with the Endangered Species Act, with the Wild and Scenic Rivers Act, with potentially threatened cultural resources, with visitor safety, with regional fire danger and available resources, with personalities among cooperators, with punishing drought, and on and on. Any fire can be shut down for one of many reasons: Gateway communities and concessioners don’t want flame and smoke to discourage tourists or to force the park to close; invasive plants can spread in the burn footprint; callouts under the California master fire plan can divert crews from prescribed fires.

And then there is the threat of wretched air in the nearby San Joaquin Valley and prolonged smoke in Yosemite Valley, uncertain and unequal funding among aspects of an integrated fire management program, and concerns over the Hetch Hetchy Reservoir (which provides municipal water for San Francisco). Any and all of these threats can encourage fire officers to end a fire. The required compromises are endless, and they all point to fire suppression as a default setting. There is no comparable checklist by which to quicken the reintroduction of fire. Even so, over the past half century, enough fire has gotten in to keep the Illilouette from detonating. Monitoring demonstrates conclusively that the basin is far healthier and more resilient than lands outside the park.

In September 2021, the park arranged for its governing cadre, along with three researchers, to trek into the Illilouette for a three-day retrospective on what 50 years of fire management had wrought. Even as the trekkers readied their gear, two fires along Yosemite’s Tioga Road continued to be managed, loose-herded into burn footprints from the previous year. To counter their smoke spreading into Yosemite Valley, two fires in the Illilouette had been extinguished earlier in the summer. The trek demonstrated the difficulties of managing fire today: not only in trying to make up losses from the past, but also in preparing for the compounding threats posed by an accelerating fire epoch. The opportunity to converse over policy and protocols while mellowing out over an evening campfire had disappeared when, two weeks earlier, the park was forced to impose fire restrictions, which left the trekkers huddled around an LED-lit lantern instead of real flames. Some of the best fire officers, fire scientists, and wilderness planners in California were unable to light a fire in a backcountry campfire ring around which they could discuss how to restore fire at a landscape scale.

More tellingly, unfolding events showed that managing Yosemite’s fires was no longer something that the park could contain within itself. Three days before the trek, a lightning storm kindled three fires in the park, and another three at Sequoia and Kings Canyon parks; Yosemite’s were extinguished, but the remaining fires soon merged into what became known as the KNP fire complex, and its smoke filled the southern horizon of the Illilouette, causing park personnel, including its fire management officer, to be dispatched to Sequoia-Kings. The fires had not stopped by the time the trek ended, and the cadre debated what they meant.

Allying with Fire

Over the past 30 years, fires have hammered at Yosemite’s border and sometimes poured through. The A-Rock and Steamboat fires in 1990 forced the park to close for the first time in its history. The Rim Fire that started in 2013 burned 104,130 hectares, some 31,000 of which were within the park. The Ferguson Fire of 2018 surged over Yosemite’s western boundary. In 2020, the Castle Fire brushed against the park’s southern perimeter, and smoke from border burns compelled the park to close twice. Further afield were all those emissions from all those fires burning fossil fuels that were collectively unhinging the climate and making climate history a subnarrative of fire history.

The park has stumbled, too. In 2009, a prescribed fire in Big Meadow intended to help protect the gateway community of Foresta escaped and blew up into a maelstrom of public and political criticism. Yosemite’s entire fire program was already immersed in a major upheaval in personnel that grumblers likened to a purge. By the time the fire organization regrouped, California was suffering a historic drought that, along with insect outbreaks and fires, would kill an estimated 150 million trees in the Sierra Nevada. Funds in fire budgets not directly related to community protection were stripped away. Fire staff positions went unfilled. Most of the park’s needed burns came from wild, rather than managed, fires.

At all levels of Yosemite’s administration, fire is now regarded as a critical issue, if not yet an existential one. A new round of reforms and restarts is underway. The park considers its fire program a “beacon” to others, and the park’s chief of staff believes the park is now headed into “a golden age of fire management.” The fire program has a full roster, and prescribed burns are lighting up Yosemite Valley, while thinning and burning projects are underway at the Merced and Tuolumne groves.

Throughout the 50-year reformation in fire management, Sequoia, Kings Canyon, and Yosemite National Parks had shared knowledge, personnel, and an origin story birthed at Redwood Mountain Grove. What happened to one was an omen for the others. In September 2021, the KNP fire complex worsened, and crews hurriedly cleared around developed areas, draped aluminum foil around the trunks of giant sequoias, and burned out along the Generals Highway that connected the parks’ various groves, hoping to back the fire down Redwood Mountain itself.

On October 4, those fires blew up. A pyrocumulus plume (a dense cloud of smoke and ash) towered over the largest concentration of sequoias in the world, and an unknown number of mature redwoods were incinerated. Combined with the 2020 season, an estimated 15 to 20 percent of Earth’s mature sequoias died. The big trees were famously adapted to fire, but not to the savagery of such burns, or likely to the severity of the maturing fire age. Hopeful observers noted that the KNP fire complex could have been worse, and that the park now had a 35,737-hectare burn scar by which to anchor future treatments such as thinning woods, setting prescribed burns, and managing wildfires.

The effort to restore fire was a revolution from the top that struggled to express itself on the ground. Policy could pivot quickly; practice could not.

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Nature demands a fire tithe, and Yosemite had managed to pay only part of it through fire restoration—enough to keep going, not enough to pay down the principle. To some observers, the debt was growing faster than it was being paid down. Neighboring Sequoia and Kings Canyon parks had 4,450 hectares of sequoias and, over the 50 years since fire restoration had become policy, it needed to treat only 89 hectares a year, but had failed. Yosemite had secured the Mariposa Grove, its biotic Parthenon, though not the grove’s periphery, and had left mostly untreated the overgrown Tuolumne and Merced groves. Even the Illilouette—a showcase project in a showcase park—has never made up its fire deficit. Other, more immediate crises, commitments, and exercises in risk aversion had resulted in half steps, distractions, and diversions, each justifiable at the time, but whose cumulative effect weakened the program.

Yosemite shows what it takes to keep fire an ally rather than an enemy—fire is a relationship, not just a tool. Yosemite also demonstrates how hard this task is, and how what seemed bold in the past might appear feeble when measured against contemporary conditions. Yosemite is a flagship national park, is the best-funded unit for fire management in the entire system, and occupies a prominent place in national fire reforms. Yet it survived by being lucky as much as by being good. Many places are neither.

Even astute observers wrestle with the three-body problem presented by natural fire, anthropogenic fire in living landscapes, and the combustion from burning lithic landscapes. They struggle to truly appreciate the extent to which fire is systemic rather than seasonal, a planetary feature not a biotic bug, a phenomenon whose plumes span from the geologic past into the geologic future. We don’t yet fully apprehend the pervasiveness of the fire age that is reforging Earth.

This article is adapted from an essay originally published in Aeon.