Wildfires threaten the world’s oldest trees—but prescribed burns are protecting them

On the U.S. West Coast, famous sequoias like the General Sherman are protected by a long history of intentionally set fires, but other giant sequoias are in big trouble.

By Alejandra Borunda
photographs by Stuart Palley
Published 22 Sept 2021, 09:49 BST
A giant sequoia burns
With its crown on fire from the Windy Fire, a giant sequoia tree rains embers onto the forest floor in the Long Meadow Grove in the Sequoia National Forest. This grove hasn't seen any fire at all for several decades, which built up fuel for the blaze.
Still from Video by Jeff Frost, National Geographic

The biggest tree in the world is wrapped in a fireproof blanket to protect it from a nearby wildfire.

The General Sherman tree, a giant sequoia in California’s Sequoia National Park and the largest tree by volume, is no stranger to fire: In its long life, the 275-foot-tall, 2,200-year-old tree has likely lived through well over 100 burns, which used to snake along the forest floor in the region every 15 years or so. The species even needs that fire to pop open its cones and release seeds that sprout its next generations.

But the fires making their way through the southern Sierra Nevada this September are not the same as burns in the past. Because of decades of fire suppression, ongoing climate- change-induced drought, and extreme heat, the fires themselves are burning hotter, higher in the forest’s canopy, and more intensely, putting to test even these most resilient and ancient of trees.

However, the General Sherman tree and its 8,000 or so sequoia neighbours have a major advantage: Their grove has been extensively treated with “prescribed fire” since the 1960s. Intentional, careful burns have helped create a healthy, resilient forest—which Christy Brigham, the chief of Resource Management and Science for Sequoia National Park, hopes can withstand a fire that could swing through.

Wildland firefighters apply a protective wrap around the base of the General Sherman Tree, the biggest tree on the planet. The giant sequoia was threatened by the KNP Complex Fire on Sunday in Sequoia National Park, California. More than 400 acres around the tree underwent a prescribed burn in 2019 to help remove fire-prone underbrush. This, and the efforts of the wildland firefighters, saved this tree and others in the Giant Forest.
Photograph by Sequoia and Kings Canyon National Park, National Park Service
After the protective wrap was secured, wildland firefighters pose with the General Sherman tree.
Photograph by Sequoia and Kings Canyon National Park, National Park Service

“It’s very open, well cared for, and there’s flat topography. If the fire gets in there, we’re expecting we’ll mainly have beneficial fire effects,” says Bingham.

KNP Complex and Windy Fires burning through the Sierras

Four active fires are now burning in the southern Sierra Nevada, where nearly all of the world’s giant sequoia trees live: the KNP Complex Fire; the Walkers Fire; and the Windy Fire.

The KNP Complex Fire, in Sequoia National Park, is burning near and slightly into the Giant Forest, one of the largest and most beloved sequoia groves in the area and home to five of the 10 largest trees in the world, including the General Sherman tree. But the Giant Forest is well prepared for fire, Brigham says; because there is little fuel near the ground, fire is less likely to jump up into the trees’ crowns.

For giant sequoias, that’s the big danger. Their thick bark—up to two feet thick in some cases—provides an effective buffer against even high-intensity fire. But if their bushy foliage hundreds of feet up burns, they’re in trouble, since it helps drive the remarkable hydraulic feat of pulling water from soil to the treetops. If the foliage is damaged, the tree can die.

A wildland firefighter hoses down flames near a giant sequoia tree in the Long Meadow Grove along the Trail of 100 Giants. The trees are threatened by the Windy Fire in the Sequoia National Forest.
Photograph by Stuart Palley, National Geographic

The park has fed the Giant Forest a steady diet of prescribed fire for over 60 years after nearly a century during which fire was actively excluded from the grove. As recently as 2019, 500 acres within the Giant Forest near the General Sherman tree were treated with intentional burns. The result is a landscape that is a veritable exemplar of sequoia-friendly habitat.

“Most of Giant Forest isn’t in the kind of peril that other groves are, or were during last year’s Castle Fire,” says Nate Stephenson, a sequoia expert with the United States Geological Survey.

So far, the fire has only lapped at the edges of the grove, approaching the Four Guardsmen, a group of four huge trees near its edge. But park scientists and staff recognised the danger to those trees last week and rushed to protect them, raking debris away from their bases so that if a fire did come rushing toward them, there would be less flammable material nearby.

Deeper issues for the big trees

The bigger worry is for groves that haven’t gotten that kind of care, says Kristen Shive, a sequoia expert and scientist at the Nature Conservancy.

Many of the 70 sequoia groves left in the Sierra Nevada are in hard-to-access locations. The trees there are often thickly surrounded by younger or smaller trees that have filled in the understory, a consequence of little or no prescribed fire or thinning.

The KNP Complex Fire has already crossed through the Suwanee Grove and is near several others, like the Oriole Lake and Atwood Groves. And the Windy Fire, south of the KNP Complex, is working its way through several other stands of giant sequoias, some of which have seen no fire at all—prescribed or wildfire—for several decades.

The fundamental issue is that fires are behaving more aggressively now than they did 10, 30, or 200 years ago, because of wide-scale changes within the forest, as well as climate change, which is drying out the landscape.

Before white settlers arrived in the West, fire crossed the land regularly. Estimates suggest at least 4 million acres of the state burned annually, a combination of lightning-ignited burns and those set by Native Americans, who used fire to manage the landscape. That is roughly the acreage that burned in 2020, and close to this year’s current total. In many parts of the Sierra Nevada, fires swept across the land as frequently as every 15 years, on average; in the Giant Forest, some areas saw fire as often as every 2 years.

Falling embers and creeping flames from the Windy Fire create an eerie, threatening glow in the Long Meadow Grove.
Photograph by Stuart Palley, National Geographic
A scorched landscape is all that’s left of this area in the Sequoia National Forest after the Windy Fire burned through.
Photograph by Stuart Palley, National Geographic

That consistent fire shaped the landscape, often leaving the forest floor much more open, less prone to high severity wildfire—intense fire that kills a lot of trees and burns so hot that it can denude even the soil— than today.

But many settlers feared and misunderstood fire and scrambled to extinguish each and every one they could. By the early 1900s, the U.S. government’s official policy, which remained until the late 1970s, was to suppress all fires as thoroughly and quickly as possible. Charcoal remnants and tree rings both show that fire frequency plummeted, dipping well below any previous period in the past 3,000 years.

At the same time, common logging practices, which removed the biggest, most fire-resistant trees and often clear cut and replanted at high density, also made the forest more fire prone. Scientists estimate that about 20 percent of the trees—many of them the biggest, oldest trees, called monarchs—were lost to saws. The result is a forest much more tightly packed with trees and other burnable material.

Then, during the record-breaking drought that gripped the West from 2012 to 2015, a huge number of trees in California died from drought and a beetle infestation—an estimated 129 million; in some areas, 80 percent of the trees died. Patches of dead trees, still standing, are woven through the state’s forests in a camouflage pattern when seen from above, grey-brown flammable tinder between the living green.

Wildland firefighters clear debris around the base of a giant sequoia tree to protect it from the coming fire.
Photograph by Stuart Palley, National Geographic

When fire encounters these fuel-rich areas, it burns like a bonfire rather than a campfire. The flames reach higher up into the forest canopy and even sometimes create the fire’s own weather, spawning updrafts that can sweep embers high into the air sometimes miles away. That all spreads fires more quickly and aggressively than in the past, burning more area at higher severity. A recent analysis showed that in California, the area stricken by these types of fires has octupled since 1984.

“We’ve been seeing fire intensity pick up over past years—climate change and past forest practices coming to a head,” says Ray Gutteriez, a member of the Wuksachi Tribe, whose ancestral homelands stretch through what is now Sequoia and Kings Canyon National Parks. “When I see the fires going on, it’s the culmination of 200 years of settler colonialism in California,” he says.

Carlos Jesus, a second year wildland firefighter from Salem, Oregon, works to extinguish flames around a giant sequoia.
Photograph by Stuart Palley

That was exactly what happened last year during the Castle Fire, which kicked off within the park boundaries in mid-August. By the time it was finally contained in January, it had merged with another fire and burned about 175,000 acres, about seven times the current fire footprints. About 20 percent of that burned at high severity.

It killed an estimated 7,500 to 10,600 giant sequoias, a stunning 10 to 14 percent of the whole population. In the groves that burned at high severity, nearly every single sequoia died—including many monarchs that had lived through scores of fires in their long lives.

The hot fires, combined with some unlucky strong winds from the east, “drove crown fires in giant sequoias. And that’s new to our experience. It killed them outright,” says Stephenson.

The Paradise and Colony Fires before they merged into the KNP Complex fire as seen from Buck Rock Fire Lookout. Both fires were started by lightning that are impacting sequoias in a more than 24,000 acres on the western slope of the Sierra Nevada range.
Photograph by Chris Boss, Sequoia and Kings Canyon National Park, National Park Service

You can’t build a sequoia

It’s too early to know how bad the effects of this fire will be, but every loss of a tree hundreds or thousands of years old causes deep grief for the researchers who work with them. On top of last year’s damage, “If we have even 5 percent more loss this year, that’s in two years—that’s really significant,” says Shive.

At the same time, scientists are hopeful that there will be good effects along with the losses. About 65 percent of the area burned during the Castle Fire did so at low or moderate severity, right in the window of what many land managers consider useful fire—and similar to what they might have done in a prescribed burn. Especially in places that had already had some treatment, the impacts could actually be beneficial to the forests.

For example, the 2015 Rough Fire—the first after the massive tree mortality became plain—burned through another set of sequoia groves.

On the part of the forest that hadn’t yet been treated is now a field of dead pines, blackened skeletons poking out of nearly bare soil. Among them stand dead sequoias as wide across as small cars.

On the other side of the narrow trail, the forest is still mostly green. This side had recently been thinned and treated with prescribed burns, and now char marks on the trunks of sequoias reach only a few feet high. Their branches, as high as 60 feet above, are still thick with lacy needles.

From raging high in the canopy, “the fire just dropped to the ground” when it encountered the treated area, says Stephenson—turning into a good version of fire, allowing seeds to pop open. Now, frothy, knee-high baby giant sequoias blanket patches near the trees’ bases, a sign of successful fire-instigated regeneration.

The challenges facing the iconic trees are not lost on visitors to the General Grant giant sequoia, the second largest tree in the world, about 30 miles north of the fires burning near the General Sherman tree. The air is thick with smoke from fires, the light tinged sunset orange in the middle of the day. But when Robbie and Lampkin Holmes, visitors from Texas, found out the southern groves were closed due to the fires, they drove a few extra hours and hiked up a hill to see this other iconic giant sequoia grove.

“Who knows if it will be here in another 30 years? We had to see it now,” says Robbie. “We build skyscrapers, but we can’t build something like that,” says Lampkin. “It’s irreplaceable.”


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