Weather Outside Your Window: Firefighters wrap world's largest trees in aluminum blankets as flames close in on sequoias

Firefighters wrap fire-resistant blankets around ancient trees — including the 275-foot General Sherman, the biggest tree by volume on Earth — as flames tear through California's world-famous Sequoia National Park.

By Monica Danielle, AccuWeather senior producer

Updated Sep. 20, 2021 2:46 PM EDT

Crews have been desperately trying to save California's famed groves of giant sequoias as multiple fires burn through the rugged Sierra Nevada Mountains.

In a rare move, the base of General Sherman, the largest tree in the world by volume at 275 feet tall and more than 36 feet wide, and other sequoias in Sequoia National Park's Giant Forest have been covered with protective foil blankets as the KNP Complex fires rage closer in recent days. The popular park's historic wooden entrance sign dating to 1935 is also covered in fire-resistant wrapping. According to California News Times, firefighters have been using this material for several years to protect various structures from flames.

During a recent fire in Lake Tahoe, some homes wrapped in the same material survived flames. The material is similar to tin foil found in kitchens but is modeled after tent-like shelters wildland firefighters use as a last resort to protect themselves when trapped by flames. The wraps aren't often used because they're costly and difficult to install, according to KoloTV.

"These trees are adaptive to fire, but not intense fire, so we want to do everything that we can to protect these trees as well as all these historic cabins that are on the national park," Steven Bekkerus, a public information officer for the KNP Complex, told Fresno ABC station KFSN.

Firefighters wrap fire-resistant blankets around the ancient trees — including the 275 ft General Sherman, the biggest tree by volume on Earth — and historic signs as flames tear through California's world-famous Sequoia National Park.

Sequoia National Park is shut down and resident employees have been evacuated along with a portion of the community of Three Rivers outside of the park's entrance.

"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.

Giant Forest 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.

A grouping of sequoias near the entryway of the park, known as the Four Guardsmen, was successfully protected from the KNP Complex fire, The Associated Press reported on Monday. It is still unknown if other famous sequoias, like General Sherman, have been hurt by the raging fires.

In this picture released by the NPS on Sept.16, 2021, firefighters wrap the historic General Sherman Tree, estimated to be around 2,300 to 2,700 years old, with fire-proof blankets in Sequoia National Park, Calif. (National Park Service)

The lightning-sparked Colony and Paradise fires, which together are being called the KNP Complex, have burned nearly 24,000 acres, according to Inciwebb.

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.

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

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.

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)

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.”

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)

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.