After the flames
As the smoke clears in California, ecologists examine the long-term impact of blazes on air, soil, and wildlife.
As firefighters mopped up after a heroic defense of historic Julian, Calif., ecologist Scott Morrison walked along a nearby ridge and looked out on a scene that many people might find discouraging.Skip to next paragraph
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A vast tract of conservation land - home to unique and endangered species of plants and animals - had gone up in smoke. Last year, a 63,000-acre wildfire scorched the land to the east of the mountains near San Diego, stopping at the ridge line under Dr. Morrison's feet. During last week's conflagration, the land to the west was reduced to a blackened, acrid firescape.
Despite this fiery one-two punch, Morrison sees encouraging signs of recovery. The ground torched by last year's fire "was really greening up, just as you would expect it to," while to the west "a lot of trees were still standing and may survive," he says.
In the aftermath of fires that have burned more than 750,000 acres and killed 22 people over the past two weeks in the Golden State, immediate concerns rightly focus on the human recovery, Morrison notes. But as people rebuild and populations grow at the edge of the wilderness, researchers are gauging the broader effects large wildfires have on air and water quality, as well as on the diversity of wildlife. Of major concern: mudslides, long-term smog, and tainted soil.
For humans, flooding, landslides, and an increase in smog can linger long after the flames are doused. For wildlife - particularly endangered species, broad-scale fires can wipe out crucial habitat. Often, habitat loss brought such species to the brink of extinction in the first place.
More broadly, scientists are getting a better handle on the impact wildfires can play in the global ebb and flow of atmospheric carbon.
"Fire is a natural part of the southern California ecosystem" as it is in many other places, says Morrison, a senior ecologist with the Nature Conservancy's San Diego office. "But now we have to come to terms with a bigger question: How does a fire of this size tip the balance ecologically?"
Indeed, researchers point out, fire as ecosystem architect has been around for more than 400 million years, when the first charcoal appears in the fossil record.
Yet its effects were likely to have been relatively limited, notes Stephen Pyne, a professor in Arizona State University's biology and society program. Without what he dubs a "biological broker" to marry a spark with tinder, wildfires waxed and waned where lightning, volcanoes, or even asteroid impacts triggered them. As a result, far more plant and animal life died from other causes than fire.
These days, wildfires make regular appearances on every continent save Antarctica. Humans trigger an estimated 90 to 95 percent of these fires - either intentionally or inadvertently - in Asia, South America, and Africa, while lightning triggers the vast majority of wildfires in North America and Russia.
In the US alone, wildfires burned more than 6.9 million acres last year at a cost of more than $1.7 billion to battle them.
One of the biggest outbreaks globally came in 1997, when wildfires in Indonesia and Malaysia pumped vast amounts of carbon dioxide into the atmosphere.
The fires' CO2 emissions equaled as much as 40 percent of the annual average emissions from human use of fossil fuels, according to a team led by University of Leicester ecologist Susan Page.
The fires played a significant role in pushing global CO2 emissions that year to the highest level since measurements began in 1957.
While concern over environmental effects from wildfires often seems to focus on charismatic creatures, many researchers are focusing on the effects fires have on soil, particularly in the steep-sloped Western states.
There, rainy seasons follow hard on the heels of the fire seasons, leading to flooding and mudslides that can extend the reach of a wildfire's damaging effect beyond its blackened borders.
Changes in soil chemistry have the potential to affect the type of plants that can return or the pace at which plants recolonize a fire zone.
"If you don't have the foundation, it's hard to bring anything back," says Peter Wohlgemuth, a hydrologist with the US Forest Service's Fire Laboratory in Riverside, Calif.
Indeed, US Forest Service officials already are moving through areas trying to determine the best strategies for dealing with erosion and flooding, which can sweep down the canyons and mountainsides with house-leveling energy.
Much of the threat stems from the post-fire dearth of plants, whose roots help hold soil in place. But, researchers say, more subtle fire effects can make the problem worse.
In regions such as the Rockies, so-called crown fires burn at temperatures in excess of 1,000 degrees F., according to Gregory Pope, who heads the Earth and Environmental Studies department at Montclair State University in Upper Montclair, N.J.
At those temperatures, organic compounds in material such as pine needles vaporize and get infused deep into the soil. The result is soil particles with a waxlike coating that fail to hold water.