California’s winter rains have quenched the last embers from the wildfires that ravaged the southern counties this past fall the biggest and most destructive in state history.
Yet the storms aren’t a source of unalloyed joy. Their effects on a landscape altered by humankind set the stage for a variety of preventable disasters.
In December 2003, rain turned a hillside denuded by the unusually bad fires into a landslide that killed more than a dozen southern California campers on Christmas day.
Heavy winter precipitation also means that non-native annual grasses brought in by Europeans and Americans with cattle and other livestock will grow lush and thick in the spring.
By late summer, these grasses will be dead and crackling dry, serving as a vast reservoir of light kindling along the borders of forests and brushlands.
Native grasses, in contrast, retain more moisture than imported grasses, and are less flammable.
The paradox reveals a bedrock fact: California’s ecology is not simply subject to fire, but predicated on it. Virtually all of the state’s terrestrial ecosystems evolved with wildfire.
Natural fire ecology
“[C]limate is the key … mild, moist winters and hot, dry summers and falls,” said Scott Stephens, an assistant professor of fire science at the University of California at Berkeley. “Ignitions are historically common … In California, seasonal fires started by both lightning and natives burned landscapes on an average of once every 10 years.”
“Many of California’s trees, including giant sequoia and Bishop pine … need fire for their seed cases and cones to open,” said Jay Watson, wildlands fire program director for the Wilderness Society. “Fire also prevents chaparral systems from getting overgrown it provides the habitat edges and niches needed to keep brushy systems biologically diverse.”
According to Watson, humans meddle with natural fire ecology at their own peril.
“It’s counterintuitive, but even if we could, the last thing we would want to do is fireproof the state,” he said. “That would bring an end to the landscape we know as California and unquestionably increase the risk of catastrophic wildfire.”
Indeed, more than 50 years of “Smokey the Bear”-style fire suppression has resulted in just that a series of huge wildfires throughout the American west over the past decade.
At fault is a buildup of fuel small, closely-spaced saplings, dead trees, heavy brush, branches and leaves on the forest floor that Watson notes ordinarily would have been burned off by smaller, periodic low-level fires.
In response to the problem, Congress recently passed the Healthy Forests Initiative, a Bush administration proposal that aims to prevent big western forest fires through aggressive thinning.
Many fire scientists applaud the new program, observing that western forests are overstocked with fuels; environmentalists generally oppose the initiative, casting it as a stalking horse for increased logging.
Until the mid-20th century, wildfires weren’t much of a social issue in the state most people lived in cities, compact small towns and farms. California’s forested areas were sparsely settled. When fires burned, they generally consumed nothing more than trees and scrub.
But things are different now.
Human beings have contributed to California’s wildfire susceptibility through fire suppression, by importing “exotic” vegetation that is particularly flammable like eucalyptus from Australia and Mediterranean grasses and choosing to live in wildland areas that are evolutionarily programmed to burn in 10 to 30 year cycles.
“The growth of ‘interface’ suburban development in wildland areas is probably the single biggest problem we face,” said Karen Terrill of the California Department of Forestry and Fire Protection (CDF). “In the past two decades especially, we’ve been increasingly forced to change our strategy from fighting wildfires to protecting homes and other structures.”
That, in turn, leads to bigger and bigger wildfires, she said, since resources expended on protecting houses can’t be devoted to actually stopping fires.
Human beings can live sustainably as part of California’s fire ecology and have played a key part in shaping California’s wildland ecologies for thousands of years.
Pre-colonial natives “farmed” oak groves and grasslands with fire, periodically burning the land to destroy intruding brush and conifers. When whites first discovered Yosemite Valley, it was an exquisite parkland of great oaks and grassy meadow, the result of meticulous and periodic burning by native Indians.
The ponderosa pine, Jeffrey pine and white fir that now predominate in the valley are relative newcomers, making their appearance only after years of vigorous fire suppression something park officials hope to remedy through an ambitious program of proscription burning.
“Fire plays different roles in different landscapes,” said Jon Keeley, a research scientist in fire ecology with the U.S. Geological Survey. “[H]eavy fuel loads resulting from years of suppression are a major factor in western fires, particularly those of the Rockies and Sierra. But fuel loads have nothing to do with southern California, which is utterly unique, an anomaly in terms of wildfire.”
The issue in the extreme southern counties, Keeley said, is the Santa Ana winds the hot, intense gusts that sweep down the western slopes of southern California’s mountains each fall.
When the Santa Anas blow as they do each year the south state burns. Nothing will alter that but an epochal change in the climate.
But human activities make the effects of the winds much worse.
California’s largest cities are unwittingly exacerbating the non-native vegetation problem by feeding these vast fuel loads, noted Philip Rundel, a biologist and fire ecologist at the University of California at Los Angeles.
“Many of these weedy fuels only flourish in highly fertile soil,” he said “[That] meant they didn’t do well in the south state, which is arid and tends to have soils with low nutrient content until recently.”
What changed, said Rundel, is in the air.
“We have a massive unintentional experiment going on downwind of Los Angeles,” said Rundel. “That windshed is heavily loaded with airborne pollutants and particulates including nitrogen … We never used to get fires in the Coachella Valley and Joshua Tree National Monument … Now, because of airborne fertilization, those areas support lush growths of annual grasses. And we’re regularly seeing burns of 1,000 acres or more.”
Some researchers say regular proscription burning of accumulated fuels would help south state forests.
For proof, they point to the 100,000 acre San Pedro Martir National Park in Baja, Mexico, about 100 miles south of San Diego.
“It’s somewhat ironic that the last large ‘natural’ California-type mixed conifer forest is in Mexico,” said Stephens. “In my opinion, San Pedro Martir is the healthiest forest in western North America. Until the 1970s, there was no fire suppression there. Low-level fires swept through periodically, destroying fuel accumulations and killing destructive insects. As a result, the forest is characterized by big, evenly-spaced, healthy trees.”
The U.S. Forest Service cites fire suppression as the reason why trees in the Angeles, San Bernadino and Cleveland National forests were weakened, making them more susceptible to the drought that has blighted southern California over the past three years.
These trees ultimately died en masse from insect infestation, creating the anomalous and highly explosive fuel reservoir that ignited in October.
Northern Baja was hit by the same drought but San Pedro Martir did not suffer the same fate as its sister forests to the north.
“In the San Bernadino National Forest, insects killed between 20 to 40 trees to the acre in the aftermath of the drought,” said U.C. Berkeley’s Stephens. “But in San Pedro Martir, the kill rate was only 1.5 trees to the acre.”
Those statistics have not been lost on the Mexican government.
“They’re re-introducing proscription burning to San Pedro Martir,” Stephens said.
Similar programs as long as they’re carried out on a sufficiently ambitious scale would also yield benefits to California, said Stephens.
But what’s also needed, agree experts, is the rigorous assumption of both private and public responsibility. Homeowners need to reduce fuels around their homes, and county and municipal governments need to look long and hard at more restrictive zoning in wildland areas.
“All you can do as a homeowner is to create defensible spaces around your structures, and you see that being done increasingly,” said Keeley. “But the idea that you can build low-density housing wherever you want in wildland areas well, that idea is coming to an end. You can’t stop these fires you can only reduce the damage by changing the configuration of the interface.”