By Andrew Hay
(Reuters) -A wildfire forced the closure of part of California's Yosemite National Park on Friday and threatened some of the largest and oldest giant sequoia trees in the world as the state faced another potentially devastating fire year.
Authorities blocked access to the park's largest stand of sequoias and told visitors to leave nearby areas, as firefighters battled the blaze, which had burned 250 acres (101 hectares) by 12 p.m. (1500 ET) on Friday, officials said.
None of Yosemite's landmark sequoias, some of which are more than 3,000 years old and have been given names, were reported destroyed by the fire, which began in the Mariposa Grove area. The cause of the blaze was unknown, a fire official said.
"There is some torching, but we're not seeing that on the named trees that's been reported yet," said Nancy Phillipe of Yosemite fire information, referring to when fire kills a tree by igniting its canopy.
The largest trees in the world by volume, giant sequoias coexisted for millennia with lightning-ignited fires that improved forest health through their natural range of the western Sierra Nevada in California.
More than a century of federal fire suppression and poor management has choked American forests with dead trees and brush that fuel wildfires, biologists say. Combined with drier conditions blamed on climate change, this has made the West's wildfires far more destructive. Fires now burn year-round rather than from early summer to late fall.
The United States is having its worst wildfire year in more than a decade, around 4.7 million acres (1.9 million hectares)burned year-to-date. That is more than twice the 10-year average, according to National Interagency Fire Center data.
New Mexico and Alaska have suffered large, intense wildfires. California is vulnerable, with nearly the entire state experiencing some level of drought.