Flames threaten giant sequoias
Ferguson Fire moving closer to the Merced Grove, one of Yosemite’s ancient sequoia forests, sending crews racing to protect the trees
As flames from the Ferguson Fire burn closer to some of the world’s oldest and largest trees, firefighters are racing to protect ancient sequoias on Yosemite National Park’s western edge.
About 25 Yosemite firefighters and restoration specialists worked Friday in Merced Grove, standing guard with a fire engine amid the immense trees that tower more than 200 feet tall and date back 1,000 years. They spent Thursday and Friday cutting back flammable brush and wrapping the largest trees with fireproof material, hoping to slow the blaze and reduce its intensity if it enters the venerable forest depicted on thousands of postcards and tourist photographs.
“It’s basically a defense,” said Scott Gediman, a Yosemite spokesman. “When you look at the fire progression and the scenarios where it could go, the Merced Grove hasn’t seen fire in a long time. We are doing it as a preventative measure.”
By Friday morning, the fire had grown to 45,911 acres and was 29 percent contained. Park officials who ordered Yosemite Valley evacuated Tuesday during the height of summer tourist season said they remain hopeful the flames will not reach the old trees. Fire operations maps show the northern edge of the blaze is not far, however — now slightly more
than 2 miles south of Merced Grove, which is located 1.5 miles south of Highway 120 near Crane Flat.
Merced Grove is one of three ancient sequoia groves in Yo- semite National Park. Although it has more than 100 sequoias, 32 are the massive giants, with trunks more than 30 feet around. Just to the north of Highway 120 is the similarly sized Tuolumne Grove. On the south edge of the park near Wawona is the Mariposa Grove, the largest and most visited of the three, with more than 500 massive old sequoias.
It re-opened last month after a $40 million renovation to remove parking lots, and construct new trails, interpretive exhibits and walkways.
The fire is not threatening the Tuolumne or Mariposa groves at this time, officials said.
Of the three, Merced Grove is considered to be the most at risk from fire, said Kristen Shive, a senior scientist at Save the Redwoods League in San Francisco.
That’s because fire crews and park scientists have used controlled burns and some thinning over the past generation in the Mariposa and Tuolumne groves to clear out unnaturally heavy growth, but not much in Merced Grove, because of limited resources. Such choked vegetation can provide more fuel for fires, allowing them to burn hotter than in centuries past, and potentially damaging the huge trees, she said.
“Giant sequoias can generally withstand fire pretty well,” said Shive, who worked as Yosemite’s fire ecologist until earlier this year. “But that’s with low-to-moderate fires, not very hot fires with big flames.”
Although not as tall as the coast redwood, giant sequoia trees are the largest trees on Earth by volume, a prehistoric species that exists today in only 68 groves in California’s Sierra Nevada range from the Lake Tahoe area to the Sequoia National Forest east of Bakersfield.
The trees actually need fire to flourish. Their cones require fire to open and release seeds. And new sequoia saplings grow best on cleared forest floors, even bare soil, that follow fires.
But more than a century of firefighting across the Sierra Nevada and Yosemite has allowed many forests to grow too thick with trees. Before the Gold Rush of 1849, fires started by lightning strikes burned through many Sierra forests every 10 or 15 years, clearing out the dead wood, shrubs and small trees. That kept lots of space between the trees, and generally meant most fires didn’t have huge amounts of fuel to consume. So most burned modestly, close to the ground.
Now, forests all over California and the West are unnaturally thick, as the warming climate increases fire risk. In some areas, such as around Lake Tahoe, there are active federal and state programs to thin smaller, sicklier trees and retain the natural balance with controlled burns.
For the past 40 years, such thinning of Ponderosa pine, incense cedar, white fir and other species has been done in Mariposa Grove after scientists noticed the big trees weren’t reproducing well. During the 2013 Rim Fire, which burned 257,314 acres on Yosemite’s northwestern edge, fire crews also conducted high-stress, emergency controlled burns in and around the Tuolumne Grove, setting backfires to protect the ancient trees as the enormous flames from the main fire advanced.
“It worked,” said Shive. “No giant sequoias there died. Fighting fire with fire works.”
Shive said she hopes the threat from the Ferguson Fire will help direct resources to reduce the risk there in future.
For now, forest restoration is a distant luxury. Crews will spend the weekend standing guard with fire engines and water tenders, hose lines and chainsaws, camped out to protect trees that were growing centuries before the cathedrals of Europe were built and Christopher Columbus set sail for the New World.
“Sequoias are really resilient,” Shive said. “It would be unlikely to have 100 percent mortality, but we could lose some. And given how precious and amazing they are, we don’t want to lose any.”