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Sequoia trees are best known for being one of the biggest organisms on Earth.

However, this well-known California lifeform faces an intensifying threat: wildfires that are burning bigger and more often due to climate change.

The giant trees grow naturally on the western slopes of the Sierra Nevada mountain range, with most of them located in a narrow, 60-mile stretch of forest just east of Fresno.

The change in fire behavior in that area was especially noticed during last year’s Castle Fire, which merged with the Shotgun Fire to create the SQF Complex Fire, said Christy Brigham, chief of resources management and science for the Sequoia and Kings Canyon National Parks.

“It is getting scary. Especially seeing one of the most fire-adaptive organisms on earth being burned up in fire. That’s a very scary change,” Brigham said.

Many of these trees have lived for hundreds or thousands of years, surviving countless fires. Last year, however, that survival rate took a hit.

“In the Castle Fire, we lost between 7,500 and 10,600 sequoias over 4 feet in diameter. That’s a lot. That’s 10 to 14% of the entire population,” Brigham said.

In many cases, fire cannot penetrate the thick bark of a sequoia, meaning the flames have to reach the canopy, something to which the trees have adapted.

“Look how far off the ground the branches are,” Brigham pointed out.

Historically, fires have also played a significant role in the tree’s ability to reproduce. Experts say every ten to 20 years, small to moderate fires would burn through and clear excess vegetation, smaller trees and other forest debris from the area.

That would clear areas underneath the trees for sequoia seeds to land and grow. The trees also rely on the heat from the fire to release those seeds, said Gretchen Fitzgerald, ecosystem staff officer of the Sequoia National Forest.

“The radiation from the heat opens up the cones, and then they drop their seeds, and they’ll drop thousands. So right after the fire this was a carpet of little, tiny, giant sequoias,” Fitzgerald said.

After the fire passes, the sequoias release sap which help the trees heal.

In earlier times, experts say this burn, heal and reproduce cycle would take place every ten to 20 years. But the introduction of aggressive fire suppression efforts in the 1930s changed that. Many times, fires were put out before they had the chance to reach large parts of the forest.

As a result, the density of the forest was allowed to grow unchecked for decades. Combined with hotter temperatures, drought and other conditions, all that dry forest buildup can now take small to moderate fires, and turn them into infernos big enough to reach the top of giant sequoias.

“This is an alarming time for giant sequoias, and for forests all throughout our Sierras,” said Tim Borden, sequoia restoration and stewardship manager of the Save the Redwoods League.

Borden and others say some of the problems can be addressed with controlled burns and other actions aimed at thinning the forest.

State and federal government agencies agree. Last year, California and the U.S. Forest Service signed a memorandum of understanding in which both sides agreed to take steps to clear what they called the “overly dense, ailing forests that dominate the landscape today.”

Both parties agreed to scale up vegetation treatment to 1 million acres of forest and wild lands annually by 2025.

“We need to get on that,” Brigham said. “We need to increase the pace and scale. Wildfires burn fast, they don’t wait for us to fill out a million forms, so we need to increase the pace and scale of our treatments.”