Weather Outside Your Window: Fires close in on iconic sequoia believed to be largest tree in world

"We have reached a tipping point," the National Park Service said about two wildfires threatening the beloved trees in California's Giant Forest.

By Monica Danielle, AccuWeather senior producer

Updated Sep. 17, 2021 4:15 PM CDT

Massive sequoias in Sequoia National Park. (AccuWeather / Brian Lada)

Sequoia National Park is shut down, its gigantic trees, some of the largest and oldest on Earth, threatened by two forest fires burning in California’s Sierra Nevada. Resident employees have been evacuated along with a portion of the community of Three Rivers outside of the park's entrance. The popular park's historic wooden entrance sign dating to 1935 is covered in fire-resistant wrapping.

"We have reached a tipping point — lack of frequent fire for the past century in most groves, combined with the impacts of a warming climate, have made some wildfires much more deadly for sequoias," the National Park Service said. The giant sequoias, which grow along the west slope of the Sierra Nevada, can be as old as 3,400 years, according to the NPS website.

Fire is burning about a mile away from the Giant Forest, which is home to more than 2,000 giant sequoias, including the tree dubbed General Sherman. It's famous for being the largest tree on Earth by volume, standing 275 feet (83 m) tall and more than 36 feet (11 m) in diameter at the base. The massive tree is a popular site for visitors who want to take in and photograph the enormous and ancient trees, and the NPS calls it a "must-see" on its Giant Forest site.

“There’s no imminent threat to Giant Forest, but that is a potential,” Mark Ruggiero, fire information officer for Sequoia and Kings Canyon national parks, told ABC News on Tuesday. The lightning-sparked Colony and Paradise fires, which together are being called the KNP Complex, have burned more than 9,300 acres as of Thursday night, according to InciWeb.

The potential threat to the giant sequoias comes just a year after several major wildfires burned in the same region. Part of the wildfire complex known as the Castle Fire destroyed 10% of the population of sequoias. “I cannot overemphasize how mind-blowing this is for all of us. These trees have lived for thousands of years. They’ve survived dozens of wildfires already,” said Christy Brigham, the chief of resources management and science at Sequoia and Kings Canyon national parks.

Park manager in the midst of dead giant sequoias killed by the Castle Fire in the Board Camp Grove, Sequoia National Park. (NPS / Anthony Caprio)

Incredibly, this past May researchers discovered a trunk of one sequoia still burning, months after the rest of the fire was contained and after an entire winter of rain and snow.

Higher-severity fires, like the Castle Fire, have killed an "unprecedented number" of the large trees, according to the NPS. Four fires between 2015 and 2020 killed many giant sequoias in groves across the Sierra Nevada. In fact, two-thirds of all giant sequoia grove acreage across the Sierra Nevada has burned in wildfires between 2015 and 2020, compared to only one-quarter in the entire preceding century.

Footprints of four wildfires that significantly impacted giant sequoia groves - Rough Fire (2015), Railroad and Pier (both 2017) and Castle (2020). Giant sequoia groves in or near the fires or shown in red. (NPS / Paul Hardwick)

Giant sequoias have lived with fire for thousands of years and have adapted. Their thick, spongy bark insulates the trees from heat damage, and flames from most fires can't reach the higher branches. In fact, the big trees need the heat from the fire to help release seeds from their cones and make clearings in the forest that allow the seedlings to grow into young sequoias. The record of burns in the rings of trees thousands of years old illustrates this symbiotic relationship to fire.

“Sequoia trees are a fire-adaptive tree,” Ruggiero explained. “It’s important to have fire to have sequoias thrive, but when we get such intense fires even the sequoias can’t stand up to them.”

The General Sherman Tree is the world's largest tree, measured by volume. It stands 275 feet (83 m) tall and is over 36 feet (11 m) in diameter at the base. (AccuWeather / Brian Lada)

The KNP complex fire is among the latest in a long summer of wildfires. California has had more than 7,400 wildfires so far this year, scorching more than 3,500 square miles and destroying hundreds of homes.