In mid-September 2021, as a lightning-sparked wildfire spread through Sequoia National Park in California, crews wrapped the base of the General Sherman Tree in a protective foil. General Sherman is the largest tree on Earth by volume, and the aim was simple: keep heat and embers from igniting the lower trunk while the fire burned nearby. The tree survived, and so did the core of the Giant Forest around it.
The images of a giant sequoia in what looked like a silver blanket travelled widely, and many headlines made it sound as if the whole tree had been fireproofed. The reality was more targeted, and the story behind it says a lot about how these forests are managed.
What happened in September 2021
A lightning storm on the night of September 9, 2021 started several fires in Sequoia and Kings Canyon National Parks. Two of them, the Paradise Fire and the Colony Fire, were managed together as the KNP Complex. Within days the complex had grown to more than 9,000 acres with no containment, and it was moving towards the Giant Forest, the grove that holds General Sherman and thousands of other sequoias.
In its updates the National Park Service explained that crews were preparing the grove ahead of the flames. That work included clearing fuel such as dead wood and brush, wrapping several of the best-known "monarch" sequoias, and protecting park buildings, staff housing at Ash Mountain and cabins in the Mineral King area. Outside the park, Cal Fire and Tulare County worked to protect the community of Three Rivers, including bulldozed fire breaks.
What the protective wrap actually does
The material is the same kind of aluminium-based structure wrap used to shield cabins and historic buildings. It reflects radiant heat and helps stop embers from settling on and igniting the surface underneath. It is not fireproof, and it cannot protect against a sustained, intense blaze.
Crews did not cover the entire 275-foot tree. The National Park Service's page on General Sherman says the lower part of the trunk was wrapped, giving the height as roughly the bottom 8 to 15 feet in different places on the page. The base is where a sequoia is most exposed: old fire scars and hollows near the ground can let flames reach inside the trunk.
The wrap was one layer of protection among several. Removing fuel from around the trees and the grove's history of controlled burning did most of the work, as the outcome later showed.
General Sherman by the numbers
According to the National Park Service, General Sherman stands about 274.9 feet (83.8 metres) tall, measures about 36.5 feet (11.1 metres) across at its widest point at the base and has a trunk volume of roughly 52,500 cubic feet (about 1,487 cubic metres). The trunk alone is estimated to weigh close to 1,400 tons.
It is not the tallest tree in the world. Coast redwoods along the California coast grow taller, and some other trees have wider trunks. What makes General Sherman unique is the sheer amount of wood in a single stem, which is why it is ranked as the largest tree by volume. Its first large branch starts about 130 feet above the ground.
The tree stands at the north end of the Giant Forest, which holds more than 2,000 giant sequoias and several of the largest trees on the planet. A short paved trail of about half a mile leads to it, and it is one of the most visited sights in the park.
Sequoias need fire, but not this kind
It may seem odd to protect a fire-adapted tree from fire. Giant sequoias have thick, spongy bark that insulates them from moderate flames, and their cones release seeds after heat dries them out. The National Park Service notes that sequoias need periodic low-to-moderate fire to stay healthy, because it clears competing plants and opens the ground for seedlings.
The danger lies in severity. A century of fire suppression allowed dead wood and dense undergrowth to pile up, and long droughts linked to a warming climate have dried that fuel out. When fire reaches such stands, it can climb into the crowns of trees that have survived for thousands of years. The 2020 Castle Fire alone killed an estimated 10 to 14 percent of the world's large giant sequoias.
How the trees fared
General Sherman came through the 2021 fires. In November 2021 the National Park Service estimated that the KNP Complex and the separate Windy Fire together killed between 2,261 and 3,637 large giant sequoias, or roughly 3 to 5 percent of the world's large sequoias. The KNP Complex accounted for an estimated 1,330 to 2,380 of those trees.
The Giant Forest itself saw reduced fire severity. The park credited decades of prescribed burning in the grove, together with new firefighting tactics used as the flames approached. In other words, the condition of the forest floor mattered at least as much as the foil on one famous trunk.
What the story teaches
The wrapping made a striking picture, but it was a last line of defence. The lasting lesson from 2021 is that groves which had been thinned and burned under controlled conditions survived far better than those that had not. Protecting sequoias for the next thousand years depends less on emergency measures and more on steady forest management: prescribed fire, fuel reduction and planting where groves have been lost.
For visitors, General Sherman is still there to see, and it remains the largest single living tree known by volume.
Sources: National Park Service: The General Sherman Tree; National Park Service: Giant sequoia mortality estimates for the 2021 KNP Complex and Windy Fire (November 19, 2021); Sequoia & Kings Canyon National Parks on Facebook; originally reported by IFLScience.
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