California firefighters gain against fire threatening Yosemite sequoias

California firefighters have gained ground in the battle against a wildfire that poses a threat to a grove of giant sequoias and a small community in Yosemite National Park.

The Washburn Fire on the western flank of the Sierra Nevada had scorched about 9.3 square kilometres but was 25 percent contained as of the early afternoon, according to an incident update on Monday.

The fire was a threat to more than 500 mature sequoias in the park's Mariposa Grove and the nearby community of Wawona, which has been evacuated.

The area in the southern portion of Yosemite was closed to visitors but the rest of the national park remained open.

Mariposa Grove and Yosemite Valley have been protected since President Abraham Lincoln signed legislation in 1864.

A sprinkler system was set up within the grove to maintain moisture, and there were no reports of severe damage to any named trees, including the 3,000-year-old Grizzly Giant.

"Fortunately, the Mariposa Grove has a long history of prescribed burning and studies have shown that these efforts reduce the impacts of high-severity unwanted fire," a National Park Service statement said.

READ MORE: Yosemite wildfire widens as crews protect giant US sequoias

No containment of fire

A heat advisory was issued for the Central Valley sprawling below the Sierra while up in the fire area, a high temperature of 31 degrees Celsius was forecast for the village of Wawona, where hundreds of tourists and residents were forced to evacuate last Friday.

"Fortunately there have not been any erratic winds that have affected fire behaviour," said fire information officer Marc Peebles.

Officially, there was zero containment of the fire but fire information officer Marc Peebles said that some percentage of containment was expected to be announced later in the day after it is confirmed.

The giant sequoias, native in only about 70 groves spread along the western slope of the Sierra Nevada, were once considered impervious to flames but have become increasingly vulnerable, as wildfires – fuelled by a buildup of undergrowth from a century of fire suppression and the impact of drought exacerbated by the climate crisis – have become more intense and destructive.

READ MORE: California forest burns as temperatures rocket in western US

Fifth of sequoias killed

Lightning-sparked wildfires over the past two years have killed up to a fifth of the estimated 75,000 large sequoias, which are the biggest trees by volume and a major draw for tourists.

There was no obvious natural spark for the fire that broke out Thursday next to the park's Washburn Trail. Smoke was reported by visitors walking in the grove.

A fierce windstorm ripped through the grove more than a year ago and toppled 15 giant sequoias, along with countless other trees.

The downed trees, along with massive numbers of pines killed by bark beetles, provided ample fuel for the flames.

So far in 2022, over 35,000 wildfires have burned nearly 1.9 million hectares in the US, according to the National Interagency Fire Center, well above average for both wildfires and acres burned.

READ MORE: California firefighters scramble to protect sequoia groves