Alarm over fire danger as California tree die-off hits 66 million

The US Forest Service provided these photos of dead trees in the Sierra National Forest. The US Forest Service provided these photos of dead trees in the Sierra National Forest. Photo: USFS Photo: USFS Image 1 of / 72 Caption Close Alarm over fire danger as California tree die-off hits 66 million 1 / 72 Back to Gallery

The California drought is carving an unprecedented path of ruin through Sierra forests, killing trees by the millions and setting the stage for a potentially devastating wildfire season that’s already burning homes and closing freeways in the southern half of the state.

Using aerial surveys that revealed stark bands of browning trees amid once-healthy green forests, the U.S. Forest Service estimated Wednesday that at least 26 million trees died between October and May, bringing the total statewide die-off to 66 million trees since 2010.

The vast stands of lifeless timber from the High Sierra to Mount Shasta are largely the result of severe water loss amid a fifth year of drought, amplified by rising temperatures and infestations of bark beetles that feast on the weakened trees. The carnage is not expected to let up soon.

The above video is a promotional video produced by the United States Forest Service showing their view of their efforts to solve the problem.

“Tree die-offs of this magnitude are unprecedented and increase the risk of catastrophic wildfires that puts property and lives at risk,” Agriculture Secretary Tom Vilsack, who oversees the Forest Service, said in a written statement.

Rushing to remove trees

The race is on to ease the danger as much as possible. The federal government, as part of an emergency task force on tree mortality created last year by Gov. Jerry Brown, is rushing to remove dead and dying trees before the peak of this year’s fire season.

The Forest Service estimates it has cleared 77,000 trees. PG&E counts more than 60,000 trees felled. And the California Department of Forestry and Fire Protection, known as Cal Fire, tallies tens of thousands more.

“We’re talking easily over 100,000 trees in total, maybe 200,000,” said Daniel Berlant, a Cal Fire spokesman. “Over the winter and spring months especially, we redirected a lot of resources. We hired seasonal firefighters months early.”

So many trees have been removed that logs are being piled up at makeshift way stations along Sierra roads, while chipping companies and bio-energy plants that process the wood are operating at capacity.

“That continues to be something we look at,” Berlant said. “What do we do with all the trees?”

The clearing efforts target areas where the fire danger is greatest, mostly in the Sierra foothills along roads, next to communities and near power lines.

“When you have a tree that is dying or is dead and it’s near our lines, it has the potential to fail and fall into our line. That would have the potential to spark a fire,” said PG&E spokeswoman Lynsey Paulo.

She said the utility expects to take down eight times as many trees this year as it did last year as part of its drought plan.

Already, the fire season has hit hard in Southern California. A pair of wildfires east of Los Angeles in the Angeles National Forest had scorched 4,900 acres by Wednesday, forcing thousands to evacuate. Farther south, the Border Fire in San Diego County grew to 6,500 acres, destroying at least two homes and 11 outbuildings. None of the fires was more than 15 percent contained.

Statewide, about 2,100 wildfires have burned close to 40,000 acres this year. While the totals are not high compared with past years, officials say, the pace of ignitions has begun to accelerate after a relatively wet start to the year.

The surge of dead trees not only makes wildfires potentially more destructive, but it also hampers the ability of forests to naturally clean vital water supplies and soak up the increased levels of carbon dioxide that have helped fuel global warming.

Assessing the damage

The Forest Service has been conducting tree mortality counts by air, with increasing accuracy, since the 1970s. The latest count reflects the results of eight flights in May over 760,000 acres in Fresno, Kern, Madera, Mariposa, Tuolumne and Tulare counties — areas where the die-off epidemic is greatest.

Jeffrey Moore, an aerial survey program manager for the Forest Service who piloted the recent flights, described the browning of large swaths of pine in higher elevations and the drying out of oaks in lower reaches.

“It’s definitely not a normal situation,” he said.

Experts say the fallout is likely to continue, as many additional trees are struggling and won’t get enough moisture in coming months or years to recover. Already, about 1.6 percent of the state’s nearly 4 billion trees have died.

“If drought persists or we’ve taken a shift overall to a drier California, we’re going to see nature take its course, and we’re going to see a loss of the forests as we know it,” said Greg Asner, an ecologist at Stanford University who studies the water content of trees.

Asner and others have speculated that hardier and more drought-tolerant shrubs and grasses could replace much of the state’s woodlands.

“It doesn’t always mean doom and gloom,” he said. “It just means major shifts in where species can be found.”

Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander