A Single Fire Killed Thousands Of Sequoias. Scientists Are Racing To Save The Rest

By Lauren Sommer

Published September 17, 2021 at 4:00 AM CDT

The 2020 Castle Fire burned the Alder Creek sequoia grove with extreme intensity, killing many of the 1,000-year-old trees there. Without any green foliage, the trees can't survive or resprout.

On a hot afternoon in California's Sequoia National Park, Alexis Bernal squints up at the top of a 200-foot-tall tree.

"That is what we would call a real giant sequoia monarch," she says. "It's massive."

At 40 feet in diameter, the tree easily meets the definition of a monarch, the name given to the largest sequoias. It's likely more than 1,500 years old.

Still, that's as old as this tree will get. The trunk is pitch black, the char reaching almost all the way to the top. Not a single green branch is visible.

"It's 100% dead," Bernal says. "There's no living foliage on it all."

The scorched carcasses of eight other giants surround this one in the Alder Creek grove. A fire science research assistant at UC Berkeley, Bernal is here with a team cataloguing the destruction.

It's not easy to kill a giant sequoia. They can live more than 3,000 years and withstand repeated wildfires and droughts over the centuries.

Alexis Bernal of UC Berkeley is with a team of researchers measuring the burned sequoias and trying to understand how so many died.

Now, with humans changing both the climate and the landscape surrounding the trees, these giants face dangers they might not survive.

Last year, the Castle Fire burned through the Sierra Nevada, fueled by hot, dry conditions and overgrown forests. Based on early estimates, as many as 10,600 large sequoias were killed — up to 14% of the entire population.

"This is unprecedented to see so many of these large old-growth trees dead, and I think it's a travesty," says Scott Stephens, fire scientist at UC Berkeley, as he surveys the damage. "This is pure disaster."

With extreme fires increasing on a hotter planet, scientists are urgently trying to save the sequoias that remain. Researchers from federal agencies and universities are teaming up to find the sequoia groves at highest risk. The hope is to make them more fire-resistant by reducing the dense, overgrown vegetation around them, before the next wildfire hits.

But one year later, the sequoia groves are again under threat. At the time of publication, wildfires burning in Sequoia National Park are within a mile of a grove with thousands of sequoias. Firefighters are battling to contain the blazes.

"It's hard to see these trees that have lived hundreds to potentially thousands of years just die," Bernal says, "because it's just not a normal thing for them."

Living more than 3,000 years, giant sequoias normally survive dozens of low-grade wildfires in their lifetimes by towering over the rest of the forest. These barely escaped the Castle Fire in 2020.

Sequoias need fire, but fires are changing

Giant sequoias only grow in isolated pockets, tucked in the mountains of California. Losing even a few groves spells significant loss to the entire population.

Sequoias are one of the most fire-adapted trees on the planet. With tough, foot-thick bark, they're insulated from the heat. They tower above the rest of the forest and the bottom of the tree is bare, without low branches that might be ignited by trees burning around it.

Old-growth sequoias weathered the low-intensity wildfires that were once the norm in the Sierra Nevada. Fires regularly spread along the forest floor, either ignited by lightning or set by Native American tribes who used burns to shape the landscape and cultivate food and materials.

With the arrival of white settlers, fire began to disappear from these forests. Tribes were forcibly removed from lands they once maintained, and federal firefighting agencies mounted a campaign of fire suppression, extinguishing blazes as quickly as possible.

That meant forests grew denser over the last century. Now, the built-up vegetation has become a tinder box, fueling hotter, more extreme fires, like the Castle Fire, that kill vast swaths of trees.

"These trees have been here 1,500 years, so how many fires have they withstood: 80?" Stephens says. "And then one fire comes in 2020 and suddenly they're gone."

Over many decades studying sequoias, Nate Stephenson had never seen old-growth sequoias die in large numbers until recently. "That's just unheard of," he says.

The Castle Fire's fierce heat was also fueled by the changing climate. In 2012, when a drought hit California, hotter temperatures amplified the toll it took on Sierra Nevada forests. While the largest sequoias could handle it, other kinds of conifers around them succumbed. Millions of trees were killed.

"The extra warmth that came with the drought pushed it into a whole new terrain," says Nate Stephenson, an emeritus scientist with the U.S. Geological Survey. "That's what really helped kill a lot of trees, and they became fuel for fires."

During his four decades of studying sequoias, Stephenson had rarely seen an old-growth sequoia die. When the first images emerged after the Castle Fire hit, he wasn't prepared.

"That's when I couldn't help it," he says. "I don't cry often, but I cried when I saw the photos. Because I love these trees."

In some sequoia groves, few seedlings are being found in the aftermath of the Castle Fire. Those that have sprouted face surviving a summer of extreme drought.

Few seedlings sprout from the ash

The soil is still powdery black in the Alder Creek sequoia grove a year later. The UC Berkeley team is scanning it for signs of hope: a spot of green.

"Two tiny sequoias here growing from the regeneration from the fire," Stephens says, finding 2-inch-tall seedlings, impossibly tiny compared to what they could become.

The lifecycle of a sequoia hinges on wildfire, which is the trigger for releasing its seeds. The blast of heat opens the cones, sending a shower of seeds to the forest floor, which get established quickly on the newly cleared ground.

In some groves, researchers are finding hundreds of seedlings where the Castle Fire burned with low intensity, the kind of fire sequoias are accustomed to.

But in the Alder Creek grove, where the fire burned with ferocious heat, the team only finds a dozen seedlings the entire afternoon. Other groves look similarly bare.

UC Berkeley's Holden Payne gathers data about the density of trees in the Alder Creek sequoia grove. Sequoia cones only release their seeds during wildfires.

Even under normal conditions, around 98% of sequoia seedlings die in their first year. This year could be even tougher with extreme drought gripping the landscape.

"I am very concerned that some areas will not have sequoias," says Christy Brigham, head of resource management and science for Sequoia and Kings Canyon National Parks. "All the adults are killed and there will not be enough seedlings to repopulate."

That's leading land managers to consider planting new sequoias, so the scorched groves don't disappear entirely. But in a changing climate, it's not a simple question. As temperatures rise, young trees planted today face surviving in a vastly different future. The most suitable habitat for sequoias could move somewhere else.

"That is one of the gifts of giant sequoias — is that they force us to think in deep time," says Brigham. "It forces us to confront the challenge of climate change."

Researchers, including Scott Stephens (left), hope to identify which sequoia groves are most at risk from extreme fires in the hope of making them more fire-resistant.

Rush to save remaining sequoias

Federal land managers say that given the millennia-length timeframe, planting new sequoias is a back-up plan at this point. The more pressing need is saving the trees that are left.

A coalition of the National Park Service, U.S. Forest Service, universities, tribes and nonprofits is banding together to identify the groves most at risk. This summer, the Giant Sequoia Lands Coalition has been rapidly assessing conditions on the ground.

"We just saw what one wildfire did," Brigham says. "Can we find the places, do the plans, and get the funding and put the people on the ground fast enough to prevent loss like this in the future?"

Brigham estimates around 40% of the sequoia groves on national park land alone are at risk of severe wildfires, because the surrounding forests haven't burned in decades. Other groves at risk are found on Forest Service or private land.

Many of the conifers within the sequoia groves were killed by California's previous drought, making them primed to burn in wildfires.

Sequoia National Park has used controlled burns, also known as prescribed fire, since the 1960s to prevent forests from becoming overgrown. But Brigham says burning continues to be a challenge.

In the spring, when cooler conditions are better for controlled burning, projects are limited because of the threatened pacific fisher. The slender, mink-like animal was listed as endangered in 2020, and its habitat is protected during the spring denning season.

But burning in the summer can be tough because of air quality concerns, extremely dry vegetation or lack of personnel, since they're generally fighting wildfires.

"There are all these constraints on prescribed fire that we can't control," Brigham says. "As it gets hotter and drier, that window is smaller and smaller."

Brigham says she's hopeful that land managers can move quickly over the next year to prioritize the sequoia groves that need help the most. With extreme fires increasingly common, time is running short.

"It is not too late," says Brigham. "We can do better. People love these trees. So I just hope we can take that love and translate it into immediate action to protect the groves and long term action to limit climate change and its impacts."