For millennia, giant sequoias — the largest trees on Earth — have resisted and relied on fire. But today’s wildfires are far more frequent and intense due to climate-fueled droughts.
In July, the Mariposa Grove of giant sequoia trees in Yosemite National Park narrowly avoided disaster in the Washburn Fire due to quick action and long-term planning.
Here are some ways sequoias co-exist with fire and how humans are protecting them from the increased threats they face.
Fighting Fire with Fire
Drought across the western United States and high winds, amplified by the slow creep of climate change, are only two of the many factors contributing to why wildfires have grown in severity over the last few decades.
Fire prevention tactics from 1870 to 1970 created an excess of fuel material on the forest floor that would have otherwise been consumed by the natural wildfire cycle. Combined with years of drought, the forests are now extremely susceptible to lightning or a careless human starting a blaze.
Over the last half century, fire experts at Yosemite have attempted to mitigate wildfire spread and intensity by deliberately setting smaller fires, a technique called a prescribed burn that was used by the indigenous populations in the area before settlers and fire suppression arrived.
“Having to protect sequoias from fire is a very new phenomena, so we’re trying things out,” said Garrett Dickman, a biologist with Yosemite National Park. “And really the thing that seems to work is prescribed fire.”
Located in the southern portion of Yosemite National Park, the Mariposa Grove is home to over 500 mature giant sequoias. It is the largest group of sequoias in the park, with many trees over 2,000 years old.
“Mariposa Grove is one of only about 75 giant sequoia groves on the west slope of the Sierra Nevada, and it’s one of the most important,” said Athena Demetry, a restoration ecologist at Yosemite National Park. “It’s where the national park idea was born.”
This grove, along with Yosemite Valley, were among the first lands to become national parks when President Abraham Lincoln signed legislation protecting the country’s natural beauty and resources.
Urgent Action Needed
Another potential threat to the sequoias, the Oak Fire ignited just 10 miles from Yosemite about two weeks after the Washburn Fire, destroying more than 190 structures and prompting thousands of evacuations. The Oak Fire has been largely corralled but further highlights the wildfire danger in the area.
In just six years, between 2015 and 2021, more than 85% of giant sequoia groves burned in wildfires, compared with 25% in the 100 years prior, according to the National Park Service. The United States Forest Service has responded to the threat, declaring they will strive to reduce severe wildfire likelihood in 12 of the 37 groves under their jurisdiction.
“Without urgent action, wildfires could eliminate countless more iconic giant sequoias,” said Forest Service Chief Randy Moore in a statement released by the U.S. Department of Agriculture’s Forest Service.
Teams of Forest Service employees, firefighters and contractors will reduce surface and ladder fuels, remove small trees and conduct prescribed burns on approximately 13,000 acres where fire experts have determined the giant sequoias are most susceptible. Efforts beginning this month are expected to conclude in November 2023.
“This emergency action to reduce fuels before a wildfire occurs will protect unburned giant sequoia groves from the risks of high-severity wildfires,” said Moore.
This tactic proved effective in the case of the Washburn Fire where prescribed fires and ground clearing in Mariposa Grove sent the fire around instead of through the grove of ancient trees.
“It’s such a sacred ground, and protecting those trees is so important to us,” said Sarah Platt, a spokesperson and wildland firefighter for Yosemite National Park.
“Giant sequoias are the root of Yosemite National Park.”