California’s lost trees

Near Placerville, the U.S. Forest Service runs a large nursery where seedling conifer trees are grown in pots and, eventually, planted in charred areas of forest recently destroyed by fire. The facility’s purpose is to help keep California’s mountains forested. But in the past decade, wildfires have become so large and destructive that, even with Forest Service crews busily planting baby trees in the mountains, the wooded areas are unable to recover as in previous years.

“We’ve been replanting as fast as funding and human energy allow, but we can’t keep up,” said Joe Sherlock, a regional silviculturist with the Forest Service.

Part of the problem is that wildfires, fueled by decades of debris buildup and drought, have become so large that they leave vast areas of charred land too far from adjacent wooded areas for seeds to naturally reach the burnt soil. Much of this land is also too remote for Forest Service replanting crews to reach.

These ravaged burn zones serve as blunt reminders of how warming trends combined with California’s drought are leaving their marks on the state. According to forest management agencies, unprecedented environmental conditions have turned the West Coast’s wildfire “season” into a year-round affair that doesn’t allow forests—and the people, plants and animals living in and around them—to catch their breath.

In fact, according to a recently published study from UC Davis, some land in California has remained conspicuously treeless for as long as seven years after a large wildfire.

“What we found is these large, high-severity fires have created huge islands of burned area where seeds aren’t able to fall,” said Kevin Welch, the lead author on the study and a research associate with the UC Davis Department of Plant Sciences.

Welch, whose research was published in December in the journal Ecosphere, says climate change is contributing to the increased size and frequency of California’s wildfires by creating warmer, drier conditions.

He and his colleagues also observed that intensified fires have upset the forest ecosystem in a novel way. They studied 14 burned areas from the Sierra Nevada to the Coast Range and concluded that the state’s beleaguered forests are not only too big for natural seedfall to reestablish them; they are also facing direct competition from hardy, fast-growing shrubs that are rapidly recolonizing burned landscapes faster than most trees can grow back.

Welch says several shrub species of the genus ceanothus have proven themselves quite fire tolerant and are sprouting through the ashes where trees and their root systems have been entirely destroyed by fire. The dense shrubbery layer could make recovery of trees even more difficult—especially for pines, which are not very tolerant of shade and will have difficultly sprouting from seed in overgrown areas.

“The pines have a really hard time growing up through the shrubs,” Welch said.

It isn’t only fire that’s killing trees. So is thirst. The Forest Service has estimated that about 100 million trees have died slow deaths from wood-boring insects with depleted sap reservoirs to defend against them during the last five years of extreme drought.

With so many trees dead or dying, impacts will trickle down through the environment. Wild animals have already taken a direct hit.

“In these large burned areas, we no longer have habitat for the spotted owl, or habitat for the marten,” Welch said. “We see a loss of biodiversity.”

Even this year’s welcome procession of winter storms has come too little, too late—and may cause disastrous erosion in burned areas, since heavy rainstorms can wash away mountainsides where tree roots once held soils together.

This can be a huge problem for municipal water suppliers that receive runoff from the burned areas. Andy Fecko, the director of resource management at the Placer County Water Agency, says the costs of removing sediment and logs from reservoirs and, especially, dam intakes run about $10 million per year in his district alone.

Fecko says ash and topsoil erosion is an issue for the first two years or so after a fire. Larger debris, like cobblestones, continue tumbling downhill for roughly five years longer.

“And with logs, we’ll keep getting them for 15 to 20 years,” he said.

Charred logs burnt in 2001’s Star Fire are still clogging the hydroelectric intake of a small hydroelectric reservoir on the Middle Fork of the American River, Fecko says.

Fires have always burned through the Sierra Nevada’s forests. However, in the past few decades, several unprecedented conditions have combined to make regrowth especially difficult for certain tree species. The climate, scientists agree, is creating warm, dry conditions in which fires can burn uncontrollably.

Another problem is the way in which forest managers have been aggressively stamping out almost every blaze small enough to subdue. Since small fires burn through low-lying shrubbery and dead wood, the government’s use of fire retardants to eliminate such natural burn cycles has allowed fuel loads to accumulate to explosive hazard levels.

In fact, many foresters now agree that fire suppression ultimately backfires and, in many parts of the world, has made blazes worse in the long run.

Welch says loggers have also contributed to California’s worsening fires by selectively cutting certain trees—especially ponderosa, Jeffrey and sugar pines—to the point where these commercially valued species are relatively rare compared to Douglas fir and white fir, now dominant in many wooded areas. As it happens, pines, with thicker protective bark, are naturally more fire resistant than firs. This means the altered, fir-dominated ecosystems are especially vulnerable to burning to the ground.

But, though on state land, these are national forests under federal authority, and it remains unclear how the new administration will respond—or if it will—given President Donald Trump’s stated disbelief in climate change.

Sherlock, with the Forest Service, says the size and frequency of fires in recent years has outpaced the agency’s manpower. A single person, working on relatively level terrain, can plant as many as 1,000 seedling trees per day, Sherlock says. That’s enough to replant four acres in a day and, in a season of hard work, perhaps a few hundred acres for one crew member.

But even with crews working statewide, it isn’t enough. “It takes a few years to clear out the debris and reestablish a burned zone,” Sherlock said. “And by then you’re confronted with another large fire.”