By Alex Fox – June 11, 2021

Last year, California’s Castle fire may have killed off ten to 14 percent of the world’s giant sequoias, reports Joshua Yeager of the Visalia Times-Delta.

The tally of dead trees comes from a new draft report that used satellite imagery, forest modelling and surveys to revise initial estimates of how many titanic trees were lost when flames ripped through parts of Kings Canyon and Sequoia National Parks. That initial estimate was around 1,000 dead sequoias, but now scientists with the National Park Service and U.S. Geological Survey (USGS) suspect between 7,500 and 10,600 mature trees may have died, reports Kurtis Alexander for the San Francisco Chronicle.

Per the Chronicle, among the fallen is the planet’s ninth-largest giant sequoia, nicknamed the King Arthur tree. Sequoias can live for thousands of years and grow to more than 250 feet tall and measure 30 feet in diameter, per the Chronicle.

“The whole thing is surprising and devastating and depressing,” Christy Brigham, chief of resources management and science at Sequoia and Kings Canyon National Parks and lead author of the report, tells Alex Wigglesworth for the Los Angeles Times.

Researchers were surprised by the death toll because of how adapted to living with fire giant sequoias are. Per the LA Times, sequoia bark can be two feet thick and their cones only release their seeds to spawn the next generation when they’re toasted by low intensity fire.

Brigham tells the LA Times that losing so many mature trees to a single fire signals the fact that climate change and a century of fire suppression have rewritten the rules that once governed the sequoia’s domain.

“They’re one of the most fire-adapted species on Earth, and that is one way that this really is a warning sign much bigger than the trees themselves,” Brigham tells the LA Times. “If we’re looking at forest fires that can now kill these old trees that have survived dozens, if not 100 or more previous wildfires, that’s a very bad sign.”

Some researchers involved in cataloguing the losses were overcome by emotion. “Not much in my life in the natural world has made me cry, but this did,” Nate Stephenson, an ecologist at the USGS who has been studying sequoias for 40 years, tells the Chronicle. “It hit me like a ton of bricks.”

The Castle fire was sparked by lightning and burned from August to December 2020. The inferno scorched 175,000 acres of parkland in the heart of the giant sequoia’s extremely limited natural range before being contained by fire crews. Like many of California’s fires in recent memory the blaze burned very hot because of built-up, tinder-dry fuels covering the landscape, reports Jack Herrera for the Guardian.

These hotter fires are more deadly for trees, even ones that have stood the test of time. Each of the thousands of mature giant sequoias estimated to have died in the Castle fire had a trunk of at least four feet in diameter. These trees would have been between 100 to 200 years old—though some may have been up to 3,000 years old, according to the LA Times.

Fire suppression was not always the law of the land in California. Per the Visalia Times-Delta, Native American tribes living in the Sierra Nevada managed the landscape using frequent, low-intensity fires for thousands of years before the arrival of settlers. Those fires, along with natural flames, may have once burned 12 million acres a year across California, reported Alejandra Borunda for National Geographic in January.

But once settlers arrived, they killed or displaced millions of Native people and instituted a new regime of fire suppression. This led to overcrowded, fuel-laden forests that land managers are still dealing with today despite so-called prescribed fire having been used by park managers in Sequoia and Kings Canyon since the 1960s.

The park now burns about 1,000 acres a year, but Brigham tells the Visalia Times-Delta that burning around 30 times that area might be necessary to get things back on track.

With the loss of trees that were thousands of years old, the forest is not going to return to what it once was anytime soon, even if new sequoia seedlings take root to replace every towering giant that was destroyed by the flames. But that distant return to the forest’s former glory isn’t guaranteed.

Stephenson tells the LA Times that some of the areas where the fire burned most intensely could come back as fields of shrubs. “It’s conceivable that if it continues to warm and warm and warm, you might not get anything looking like the forest used to be there coming back in,” he tells the LA Times.

Still, 90 percent of these majestic towers of living wood still remain and now that snow has melted in the mountains, Brigham and other scientists will put boots on the ground to see if things are as bad as they fear. “I have a vain hope that once we get out on the ground the situation won’t be as bad, but that’s hope—that’s not science,” she tells the LA Times.

According to the Chronicle, managers also plan to identify the groves of giant sequoias that are most at risk going forward, set prescribed fires, and take other restoration actions in hopes of making them more resilient.