Why giant sequoia trees are surviving now when others died in recent fires

YOSEMITE NATIONAL PARK — Last year and the year before, in an unprecedented environmental disaster, wildfires in California’s Sequoia National Park and nearby national forests roared through treasured sequoia groves in the Southern Sierra Nevada, generating flames hundreds of feet high and killing nearly 20% of all the giant sequoia trees left in the world.

But the Washburn fire burning now in Yosemite National Park, licking around the edges of the roughly 500 giant sequoias in Mariposa Grove — some over 200 feet tall and more than 2,000 years old  — so far hasn’t killed a single one of the massive old-growth trees there.

A big part of the reason, experts say, is that park officials completed 23 projects at the grove since 1971 to thin brush and set controlled burns to remove dead wood and vegetation that had built up over more than century of fire suppression.

That left less dead material on the forest floor, and fewer shrubs and small trees like firs that can make fires burn hotter. As a result, the forest was restored to a more natural condition, experts say, similar to the way it would have looked centuries ago when lightning strikes and burning from native tribes sent low-impact fires through the Sierra every 10 years or so.

In recent days, firefighting crews also were able to build hand lines around the famed grove, and set up a sprinkler system next to the Grizzly Giant and several other massive sequoias.

“We’ve lost no giant sequoias, and the outcome’s looking better every hour,” said Yosemite fire ecologist Garrett Dickman.

Although air drops of fire retardant have helped, he said, controlled burns, the most recent of which was done in 2018, have been key. Dickman said about a dozen sequoias in the grove were scorched by the fire but none were killed.

“The fire that they got came in at relatively low intensity,” Dickman said, “well within their ability to withstand.”

By Tuesday afternoon, the Washburn Fire had grown to 3,221 acres. It was 22% contained, with 649 firefighters on hand. Yosemite Superintendent Cicely Muldoon said Monday night at a community meeting that the fire was “human caused” and remains under investigation.

As the drama plays out, the fire is being cited as an example of how other giant sequoia groves across the Sierra can be saved in an era of hotter, more intense fires made worse by climate change.

A firefighter protects a sequoia tree as the Washburn Fire burns in Mariposa Grove in Yosemite National Park, Calif., on Friday, July 8, 2022. (AP Photo/Noah Berger)

“Prescribed fire works,” said Nate Stephenson, a scientist emeritus with the U.S. Geological Survey who has studied giant sequoias for decades. “It greatly improves the odds of a good outcome.”

Giant sequoias evolved over millions of years with low intensity fire. Not only does fire remove debris from the forest floor to allow new plants to grow, it also generates heat that opens sequoia cones and releases their seeds. Although coast redwoods are the tallest trees on earth, giant sequoias, their biological cousins, are the largest by volume, with bark that can be 2 feet thick and resistant to fire. As a result, individual trees are often 1,000 to 3,000 years old, having survived many fires.

But starting in the late 1800s, settlers began dousing lightning fires. Native tribes who set fires for centuries were removed from the land. And the forests became thicker, more choked with dead wood and smaller, flammable vegetation.

In 2020, the SQF Complex fires, started by lightning, killed 7,500 to 10,600 giant sequoias in Sequoia National Forest in Tulare County. The following year, the KNP Complex and Windy fires killed another 2,261 to 3,637 giant sequoias in Sequoia National Park, Sequoia National Forest and surrounding lands.

Stephenson said those fires burned much hotter in groves that had not had any controlled burns.

“Areas that had not seen a recent prescribed fire did really poorly,” he said. “They were moonscaped. It was awful. Not a living sequoia left. Areas that had prescribed fires mostly did really well.”

There are roughly 78 giant sequoia groves over a 250-mile long range in the Sierra Nevada. They total about 25,000 acres, and exist nowhere else on earth.

Save the Redwoods League, a San Francisco non-profit that has worked for 100 years to preserve redwoods and sequoias, estimates it will cost $500 million to treat about 60,000 acres of giant sequoia groves and the forests around them over the next five years with controlled burns and thinning, said Sam Hodder, the group’s president.

“There is an existential threat to the species,” Hodder said Tuesday. “What we have seen in the last five years, in terms of mass mortality events in giant sequoias, is unlike anything we have found anywhere in the tree ring data going back thousands of years.”

Hodder’s group is supporting a bill introduced in the House of Representatives last month, the “Save Our Sequoia Act,” to provide more federal funding and streamline paperwork requirements to allow more controlled burns. The bill has bipartisan supporters, including Rep. Scott Peters, D-San Diego, and Rep. Kevin McCarthy, R-Bakersfield.

Controlled burns can cause controversy because they generate smoke. They also have at times generated opposition from some environmentalists, can be expensive, and occasionally burn out of control. But it can be cheaper, Hodder notes, to take steps to reduce fire risk among some of America’s most iconic landscapes than to battle big fires on them.

“Much of that landscape is vulnerable to catastrophic wildfire,” he said. “Mariposa Grove is showing that the combination of fire and good stewardship to reduce the fuel load can lead to resilience.”

Stephenson said even with climate change, the situation is not hopeless, if people act.

“I really want my grandchildren to walk among living 2,000 to 3,000-year old sequoias and get that sense of awe,” he said. “It’s moved me so much. It has moved people all over the world. They are inspiring.”

Bay Area News Group writer Jason Green contributed to this story. 

Yosemite Conservancy President Frank Dean walks on a new boardwalk trail in the Mariposa Grove of Giant Sequoias on Tuesday, June 12, 2018 in Yosemite National Park, Calif. The grove has been closed for three years while a $40 million restoration project has been completed. (Aric Crabb/Bay Area News Group)
Yosemite Conservancy President Frank Dean walks on a new boardwalk trail in the Mariposa Grove of Giant Sequoias on Tuesday, June 12, 2018 in Yosemite National Park, Calif. The grove, now surrounded by the Washburn Fire, was closed for three years while a $40 million restoration project has been completed. (Aric Crabb/Bay Area News Group)


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