By Bettina Boxall
6:30 PM EDT, September 23, 2013
TUOLUMNE, Calif. — Tourists stopped at the Rim of the World overlook on California 120 earlier this month to take photos of the panoramic view — just as they always have.
But they stared in silence at the ashen hues of a landscape swept by the largest wildfire to burn in the Sierra Nevada in more than a century of recordkeeping. Steep canyon walls and mountain slopes that had been robed in chaparral and oak were now draped in black, spreading to the horizon in a funereal scene.
To the north, miles and miles of forest were still and lifeless, the earth scoured by flame. Millions of charred trees stood naked, their needles incinerated.
The huge Rim fire, ignited Aug. 17 by a hunter's illegal campfire, is likely to have transformed large swaths of the Stanislaus National Forest for decades to come.
Remote sensing satellite images indicate that virtually all of the vegetation is dead on nearly 40% of the area of the 401-square-mile blaze, which burned from the national forest into the western portion of Yosemite National Park, where it continues to smolder.
Burned chaparral and oak will quickly resprout. But where large patches of trees were killed, ecologists say it could take 30 to 50 years for the forest to reestablish itself in the shrub fields that are the first to grow. If there are more fires in the meantime, the land could permanently convert to chaparral.
"You're looking at a huge area that doesn't have any living conifers," said Hugh Safford, regional ecologist for the U.S. Forest Service. "The big question really for managers and the public is what's that landscape going to look like in 50 to 100 years. It's going to look really different."
The fire started in chaparral midway up Jawbone Ridge on a Saturday afternoon not far from the Rim overlook — thus its name. Flames sprinted up the canyons into higher elevations. On a couple of days with high winds, the blaze grew explosively, racing through more than 30,000 acres in a single day.
The fire chewed through expanses of ponderosa pine and other conifers. It charred young tree plantations that had been planted after previous wildfires. It scorched some of the last remaining old growth in the Stanislaus, downed power lines and crept up to Hetch Hetchy Reservoir, the source of San Francisco's water.
Like all wildfires, it was temperamental. Sometimes it burned furiously, sometimes slowly and sometimes barely at all. That has left a mixed palette of black, brown and green within the fire boundaries.
About 29,000 acres were largely untouched by flame, according to the vegetation survey, which compares remote sensing images of the burn area with images taken before the fire.
Two weeks ago, dozens of federal scientists from around the country set out to assess the damage and plan emergency recovery efforts. They fanned out across the forest, digging holes to see if the soil would hold water or repel it in erosive sheets. They checked trails and roads and known archaeological sites.
They tramped through plantations and forestland that had been previously thinned or burned in managed fires to see if the treatments had succeeded in taming the flames.
Curtis Kvamme, a Forest Service soil scientist who was on his fifth day of poking in the dirt, took a shovel to scrape a thin layer of ash from the ground in an area of badly burned timberland. With his gloved hands he carefully exposed the soil, then squirted water in a zigzag pattern onto the ground and watched what it did. It beaded.
"High repellency starts at about 3 inches," he told his colleague, Kellen Takenaka, who was recording the information in a small hand-held computer.
Kvamme's verdict: The soil had burned at high severity, meaning there is a greater chance of erosion. Instead of seeping into the earth, rainfall or snowmelt could wash in torrents downslope, potentially contributing to flooding.
"This is cooked, a lot of acres burned pretty intensely," said Todd Ellsworth, a Forest Service watershed manager who oversaw the post-fire survey, known as Burned Area Emergency Response. The team will recommend steps, such as straw mulching, in areas with a high potential for erosion and runoff that could damage roads or clog streams and rivers with sediment.
When the soil survey results were released a few days later, the findings were better than expected. The soil had burned at high severity in only about 7% of the Rim blaze. The ground burned at low severity or was unburned in 56% of the acreage.
But those numbers don't reflect what happened above ground. Satellite imagery reveals hardly a speck of green on one block of 33,593 acres of trees and shrubs. On one 16,445-acre patch of conifers, nothing appears to have survived.
Severely burned tree patches that big leave a paucity of seed sources, making it that much harder for the forest to regrow.
"We have … miles and miles of mortality," said botanist Jennie Haas, who has worked in the Stanislaus for more than three decades. She has seen some seeds floating through the ghostly landscapes — what she called "little rays of hope."
"But if we don't intervene, it will convert to brush," she added.
Intervening means salvage logging, clearing out the charred trees that are of no value and replanting. The process is opposed by many environmentalists who point out that a thriving post-fire ecosystem emerges in burn areas, drawing bird and other species found only in blackened forests.
Allen Johnson, a retired fire management officer for the Stanislaus, and Morris Johnson, a research fire ecologist with the Forest Service, stood on a ridge overlooking a large bowl. It had burned in the 1973 Granite fire, was salvage-logged and then replanted with ponderosa pines. The nearly 4-decade-old trees now resembled an army of black sticks marching across the slopes.
"You look right here and it killed everything," said Allen Johnson. Then he gestured behind him to a stand in which the pines still had their needles, although they were almost entirely brown, scorched by the fire's heat and unlikely to survive.
In the scorched stand, the flames had been only a few feet high. In the bowl, which resembled the inside of a doused campfire, the fire had been much more intense, consuming the tree crowns.
The difference, at least in part, could be explained by the fact that about six years ago, the scorched stand was thinned to reduce tree density. "Did it change the fire behavior? Yes, it did," said Allen Johnson. "Did it save the trees? No."
The two men had spent days driving in smoky haze around the Rim burn area to examine stands that had previously been thinned or had undergone prescribed burns to reduce fuel levels. They will prepare a report as part of a new Forest Service program that is evaluating the effectiveness of such treatments in wildfires across the country.
The Rim is the latest in a string of fierce blazes that have hit the Sierra and the Southwest in recent decades, the result of what scientists say is a combination of factors.
Extensive logging in the last century and late 1800s removed most of the big, old-growth trees that are the most fire resistant. The government's war on forest fires, launched in the early 1900s, put an end to the frequent, low-intensity wildfires that for millennia had kept fuel levels in check in much of the Sierra. Warming temperatures and drought are lengthening the fire season and drying out fuels, leaving wild lands more flammable.
Analyzing fire scars in the stumps of ancient giant sequoias in the Sierra, Thomas Swetnam has compiled fire records going back 3,000 years showing that wildfire frequency plummeted with the arrival of the settlers.
"What's missing in these forests really has been the surface fires," said Swetnam, director of the University of Arizona Laboratory of Tree-Ring Research. "It's true enough that high severity, stand-replacing fires are not totally abnormal. But it's the size of them and the extent of them that is unusual."
Safford expects more Sierra fires like the Rim.
"We're going to see a bigger one than this at some point," he said.
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