The Perfect Firestorm
Welcome to the new era of "megafires," which rage with such intensity that no human force can put them out. Their main causes, climate change and fire suppression, are fueling a heated debate about how to stop them.
The physics create nature's own special effects studio. A smoke plume can form a pyrocumulus cloud. Sometimes the plume rises to the troposphere/stratosphere boundary, at between 25,000 and 40,000 feet, where cooler temperatures stop it. That creates heavier, wetter air that may descend again and create a windstorm and microbursts as it returns to earth, literally fanning the flames. Megafires can also create "fire whirls," mini tornadoes of spinning flame that can peel off and set their own course, ripping 16-inch limbs off of oaks and generating winds of more than 80 mph. Says Wayne Cook, who has more than 30 years of firefighting experience, "The bottom line is, once you get to that scale, there is nothing you can do to put the thing out until the weather changes."
The Rocky Mountain Climate Organization reports that from 2003 to 2007, the 11 western states warmed an average of 1.7 degrees Fahrenheit, or 70 percent more than the global average. Many forecasters believe that in coming decades, the West will continue to experience later winters, less snowfall, earlier spring runoff, and generally drier conditions.
As a result, conditions are solidly in place for a political and pyrotechnical firestorm in many forested areas. The western fire season is now 205 days, 78 days longer than in 1986. What's more, there have been four times as many fires that wiped out more than 1,000 acres than there were in the 1970-1986 period, and six times as much acreage has burned, according to an influential article in Science in 2006 by Anthony Westerling, a researcher at the University of California-Merced. Westerling demonstrated a strong link between climate change and increased wildfires.
One of the most visible effects of warming is the bark beetle infestation that has killed billions of conifers across millions of acres. Deep-freeze winters that once killed off the beetles are mostly a thing of the past. Just how much fire danger these dead forests pose is the subject of scientific debate--and some intriguing hypotheses. On the face of it, scattering the forests with kindling would appear to raise the fire risk. But in an analysis of multiple studies, University of Wisconsin zoologist Martin Simard found that it's not so simple. In the first year or two after beetles destroy a forest, fire probability does, indeed, increase. But as the needles fall from the trees, the likelihood of crown fires (those that jump from tree to tree, like the ones in the Fire Lab) actually decreases. Years or even decades later, the analysis says, "when beetle-killed snags fall on the ground and understory tree growth creates ladder fuels, the risk of crown fire may again be increased."
Experts have learned that fire, like top predators, can't be removed without affecting the balance of an ecosystem. Historically, low-intensity fires periodically swept the landscape, leaving clearings that nurtured fire-tolerant species and helping create a healthy distribution of grasses, shrubs, and trees that sustained biologically diverse regions. The long-standing policy to "fight" fires has been ecologically counterproductive in many places, even though it has saved lives and property. Suppression in the Smokey the Bear era from the 1940s to the 1970s produced many unintended consequences, like a massive accumulation of dead fuel and live biomass. More single-species, same-aged forests led, in part, to unmanageable fires.
The increasing number and size of megafires is triggering changes in regional ecology--for better and for worse. Some burn so hot over larger areas that they virtually sterilize soils and unhinge energy, water, and carbon cycles. Smoke billowing from blazes alters atmospheric chemistry, causing ozone alerts thousands of miles away. In addition, burning forests release vast quantities of greenhouse gases, notably carbon dioxide. Some fish populations have crashed after big fires, and other established species lose their competitive advantages and virtually disappear.
Yet many species not only survive big fires, they thrive because of them. Richard Hutto, director of the University of Montana Avian Science Center, says fires "are one of nature's best-kept secrets" as a driver of greater biodiversity. The mountain bluebird, for instance, belongs to a category of "pouncers" that exploit the insect explosion in a newly burned forest. Black-backed woodpeckers are so enamored of burned areas that they exist virtually nowhere else, Hutto says. Northern hawk owls in Canada flock to fire-swept places, and in other forests, deer mice populations soar, opening the door for more raptors to move in. Morel mushrooms, those expensive delicacies, proliferate in burned areas. The huge 1988 Canyon Creek Fire in Montana's Bob Marshall Wilderness may have saved the Big Nell's geranium, which was thought to be extinct but actually required a good fire to bloom again. That blaze also caused an elk boom because the regenerating landscape "put a lot of new groceries out there," says Williams.
Ecologists know that changing conditions will benefit some species and harm others. Hutto agrees that trends seem to be pointing toward more, and bigger, fires but worries that policy makers don't understand that the rewards may be enormous--even from big fires. The pressure to "salvage log" on public lands after a fire is misguided, he says, because "that's where the real ecological magic begins."