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.
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.
The same process happens in southern California, where many plants adapted to the region's Mediterranean climate have waxy leaves and stems to help retain moisture during dry seasons.
In the aftermath of fires in Colorado last year, Dr. Pope says, scientists found that the layer of waxy soil reached depths of more than four inches, defying traditional attempts to reseed the burned area.
In coastal regions, interest also is growing on the effect mud flows can have if they move into sensitive offshore ecosystems, such as biologically productive kelp beds.
"We have anecdotal evidence here in Goleta Bay for fires and floods following a large drought in the 1850s and '60s" that flushed a large amount of sediment from the hills behind Santa Barbara into the bay, turning a portion of it into marshland, says Daniel Reed, who heads the three-year-old, long-term ecological research station there.
Such pulses of sediment could bury reefs and prevent marine organisms from recolonizing them.
Changes in soil
Researchers also want to understand better how the heat and ash change the mineral content in the soils. Of particular interest are nutrients and even household pollutants that can get swept down to ecosystems in lower elevations.
Through these efforts, researchers hope to better tailor soil retention techniques to local conditions. Many of the approaches currently being offered are untested, Mr. Wohlgemuth notes.
Beyond the soils, researchers are digging deeper into fires' effects on gases and particles that can trigger bad-air days long after a fire is extinguished.
"Fires have a tremendous impact on atmospheric chemistry," even after they're extinguished," says Alex Guenther, an atmospheric chemist at the National Center for Atmospheric Research in Boulder, Colo.
Globally, 90 percent of the hydrocarbons in the atmosphere come from plants. And the fires in Indonesia and Malaysia pumped a plume of carbon monoxide into the atmosphere that were tracked as it circled the globe.
Yet locally, the amount and type of hydrocarbons that plants emit vary from species to species. These differences can translate into changes in local air quality that could challenge conventional approaches to meeting air-quality standards.
After fires in Florida, for example, burned areas can be recolonized by oak or pine, Dr. Guenther explains.
Oaks give off a hydrocarbon known as isoprene, which reacts with nitrogen oxide to form ozone. Pines give off pinene, which produces less ozone but more particles.
Either way, the new growth represents a source of hydrocarbons and particulates that need to be taken into account when crafting air-quality standards and appropriate means of meeting them, researchers say.
For ecologists such as the Nature Conservancy's Morrison, however, perhaps the overarching ecological concern is for the plants and animals that may never recover from the California blazes.
He notes that following the fires in Yellowstone National Park in 1988, plants and animals recolonized the area much more quickly than many people expected.
In part, the creatures that inhabited the park fled to similar habitats outside the area, so their populations could move back relatively easily.
"We expect a good deal of the natural community to revive" after last week's fires, Morrison says, "but we're concerned about the longer-range impact. We have more species than any other county in the continental United States because we have a remarkable diversity of habitats of different ages. Now we've set the clock back to zero on all of these habitats within a very large area," leaving many of the plant and animal inhabitants with nowhere else to set up quarters.
"We've really worked hard to implement a conservation network in southern California" that tries to preserve fragmented habitats and link them with a series of corridors. The network was the fruit of seemingly endless hours of negotiation with federal and state officials, landowners and developers, and environmentalists. "A great deal of that network burned within days," he says wistfully.
• Death toll in California fires: 22
• Acres burned: more than 750,000
• Homes destroyed: 3,600
• Total acres burned in US so far this year: 3.5 million
• 10-year average of acres burned annually in the US: 4.3 million
• Total cost for federal agencies to suppress all wildfires in 2002:
• Rate of solving wildfire arsons: less than 10 percent a year
• Some of the world's biggest recent blazes:
Indonesia and Malaysia (1997-1998): more than 15 million acres
Russia (1998): 4.9 million acres
Brazil (1998): 2.5 million acres
• Percentage of wildfires caused by human activities: 90
Sources: AP, National Interagency Fire Center, Santa Clara County Fire Department