A wildfire threatening some of the world's oldest giant sequoia trees in California's Yosemite National Park expanded five-fold over the weekend.
As of Sunday, the blaze has scorched nearly 1,600 acres (648 hectares) of timber and brush at the southern end of the park, up from 250 acres on Friday, a day after fire was first reported by visitors on the Washburn Trail of the Mariposa Grove of Giant Sequoias.
National Park Service personnel immediately closed the Mariposa Grove, home to more than 500 mature giant sequoias, and on Friday evacuated the adjacent native American community of Wawona.
How are the fires affecting tourism to the National Park?
Coming at the height of the summer tourist season, the evacuations displaced an estimated 1,600 people in all, according to Park Service spokesperson Nancy Phillipe.
The Park Service also has shut down the southern entrance to the park, which Phillipe said draws about 4 million visitors a year.
The park's best-known attractions, including Yosemite Valley, remain accessible to visitors from its western entrance. But smoke and soot have dimmed views of landmarks such as the towering granite formations of El Capitan and Half Dome, as well as Bridalveil Fall and surrounding cliffs.
Federal wildfire officials on Sunday warned that air quality for particulate matter had reached unhealthy levels across much of the park.
What will happen to the ancient giant sequoias?
While flames stoked by extremely dry, hot conditions on Sunday have burned largely unchecked, none of Yosemite's landmark sequoias, some of them over 3,000 years old and given names, have yet been lost, Phillipe said.
Firefighters were taking special measures to protect the grove, clearing away undergrowth that could add to the fuel bed and deploying ground-based sprinkler systems to increase humidity levels.
"We're feeling confident of the plan we have in place today," Phillipe told Reuters.
The cause of the blaze remains under investigation, and no injuries have been reported, officials said.
Giant sequoias, the world's largest trees by mass and insulated by thick, spongy bark, have coexisted for millennia with lightning-sparked fires considered part of the natural balance of healthy redwood forests.
Fire is even vital to reproduce the trees, whose cones require high heat to crack open and release seeds.
However, experts say drought-stressed sequoias today have grown increasingly vulnerable to more frequent bouts of extreme wildfire activity symptomatic of human-caused climate change.
Thousands of the trees have perished in six major wildfires that have raged through California's Sierra Nevada range over the past six years, burning 85 per cent of all giant sequoia groves between 2015 and 2021, compared to only one quarter in the preceding century.