FRESNO, Calif. — California’s biggest wildfire was just a 40-acre canyon blaze west of Yosemite National Park on Aug. 17. In just a few days, the Rim fire grew into a monster, menacing foothill communities and incinerating landscape with 200-foot flames burning at 1,200 degrees.
Motorists 100 miles away near Sacramento saw ash-filled pyrocumulus clouds billowing thousands of feet high, as if a volcano had erupted. The still-growing Rim fire footprint is now more than two-thirds the size of Los Angeles and burning into state history — one of the five biggest fires on record.
What happened to that 40-acre fire at the Rim of the World, a peaceful overlook at the Tuolumne River canyon in the Stanislaus National Forest?
Federal scientists say the fire hit overdrive when it moved from the scar of an old fire into overgrown forest that had not burned in a century. The thick forest made the Rim fire historic.
By Saturday, it had expanded to 219,277 acres. Nearly 5,000 people still were involved in fighting the fire, which was 35 percent contained, at a cost of $54.8 million. It will be weeks before it is contained.
Experts already are saying the ecosystem damage is huge. In a terrifying whoosh, the Rim fire changed the forest for at least a generation and maybe a lot longer.
As the climate changes and more fire takes place, there is a chance big fire-resistant trees might not recover. Fields of flammable shrubs might be all that is left in some places, fire ecologists say.
Further, they say that much of the Sierra’s 25 million acres is overgrown and primed for these kinds of large, hot wildfires.
Someday, many parts of the Sierra may resemble Southern California mountains where evergreen shrublands dominate the landscape, said Hugh Safford, regional ecologist for the Forest Service’s Pacific Southwest Region and research associate at the University of California, Davis.
“If you’ve seen those mountains, you know how different they are from the Sierra,” he said. “That’s the kind of change I’m talking about.”
The key is the increase of big fires, which has been documented as the climate has warmed in the last two decades, ecologists said. These blazes quickly torch acres of vegetation — from the top of centuries-old pine and fir trees to the grasses, forbs and sedges below.
“A fire like this will kill a third to half of the forest it burns through,” said Malcolm North, research scientist for the U.S. Forest Service and forest ecology professor at UC Davis. “It is devastating.”
One reason the Sierra’s forests became overgrown was a flawed federal policy. Many decades ago before fire’s role was understood, federal authorities snuffed out all fires. The practice interrupted the frequent, low-intensity fires that kept the forest healthy in the past.
Fire suppression must continue to protect communities such as Groveland in the Rim fire, but there are some hard facts to face, North said.
Federal land managers are trying to thin the forest with controlled fires as well as cutting and clearing heavily forested areas. But there’s simply too much forest that needs thinning.
“We’ve gotten ourselves in a really big hole,” he said. “We’re not going to dig our way out the way we’re doing it now.”
The problem now is compounded by waves of nitrogen from some of the nation’s worst ozone air pollution in the San Joaquin Valley. It amounts to a mega-dose of fertilizer wafting into the Sierra’s western slope.
The situation makes fire authorities nervous every summer, particularly this year after two dry winters. The massive Rim fire probably will burn until storms hit in autumn.
Next year, kayakers will see the devastation as they glide down the Tuolumne, said Safford. He said scientists won’t know the extent of the damage until they investigate after the smoke clears, but there is little doubt about what they will find.
“The Tuolumne River canyon will be fundamentally different over the next 50 years,” Safford said.
The fire recovery will be dominated by shrub species, such as chaparral, which is highly flammable, he said. More chaparral also will be apparent in Yosemite where the fire has burned more than 40,000 acres.
Will the trees come back at some point? They should eventually return, said Yosemite-area scientist Jan van Wagtendonk, research forester emeritus with the U.S. Geological Survey’s Western Ecological Center.
“But if another fire burns through, it goes right back to chaparral,” he said. “That has happened already in some places.”