Fires of Life
Stewart, Doug, National Wildlife
From the skies over south Florida's Big Cypress National Preserve, a helicopter routinely drops small incendiary devices into the dry grass. War games for the National Park Service, perhaps? Training grounds for a fire department? Actually, the point here is just what it appears to be: setting fires. Airborne rangers routinely torch the park in order to nourish it.
The idea, says Big Cypress wildlife biologist Deborah Jansen, is "to replicate lightning strikes as closely as possible." Fires are essential to keeping open the wet prairie that covers parts of the 700,000-acre preserve. Explains Jansen, "When fire comes through, it brings in new growth, which is more palatable than older vegetation to the deer and feral hogs we have." Well-fed deer and hogs make for well-fed Florida panthers. Only 30 to 50 of the endangered felines are thought to exist; 15 stalk Big Cypress and its environs.
That searing flames could help rescue a tiny band of animals from extinction may not seem terribly logical to nonbiologists, especially those of us raised to equate big fires with the ecology of hell. Right now, residents of the drier parts of the country, especially in the West, are girding themselves for the home-threatening forest and brush fires that seem to strike every year around this time.
Yet to ecopyrologists (those who study the ecology of fire), nature without fire, in most places, would be unnatural indeed. A good number of the Earth's species evolved in concert with lightning-caused fires, and many depend on flames for their survival. Biologists are now struggling to temper civilized humankind's tendency to battle any and all fires, a tactic that can bring an unwanted stillness to once-thriving wildlife habitats.
U.S. Forest Service botanist Larry Stritch recalls a sad patch of flora in the rolling oak-hickory woodlands and savanna of Illinois' Shawnee National Forest a few years back. "There were prairie wildflowers that were barely hanging on among the leaf litter, not even blooming," he says. Some of the prairie grasses were tall-grass varieties in name only.
Within a month after the second of two controlled, low-intensity fires burned away much of the shrubby understory, the scene changed dramatically. "There was a solid carpet of flowers, forbs and grasses everywhere you stepped," Stritch says. "Sunlight was actually hitting the ground." Post-fire rains had soaked the soil with a flood of nutrients from the ash of burned plants. Seeds that had lain dormant just underground for years had sprouted in profusion. Botanists tallied 63 new plant species.
So-called edge species, found where fields border woodlands, now thrive throughout the area's parklike mixture of clearings and groves. Sparrows and butterflies flit in and out of the sunlight beneath the patchy woodland canopy, and wild turkeys have appeared for the first time within memory. Goldfinches are drawn by the reappearance of thistle, which yields puffy down the birds use to build their nests. "We're amazed by the number of species that came back," Stritch says.
Controlled burns like these wouldn't be needed in wildlife habitats around the nation if natural fires hadn't been stamped out whenever possible for nearly a century. Over time, fire suppression changes a landscape. Grassy clearings close up. Swamps fill in with vegetation and dry out. Once-open areas under trees can turn into a nearly inpenetrable tangle of young, trees and woody brush known as a "dog-hair thicket."
As vegetation becomes more uniform over large areas, some animals lose elements of their ecological niches, just as the goldfinch loses its thistle. A savannah that once hosted herds of elk, bison and deer - along with bears, wolves and a multitude of birds and insects - ultimately becomes home mostly to ravens, squirrels, porcupines and a few other deep-woods birds and rodents.
Most wildlife biologists and park managers would agree that a given landscape is healthier when it supports abundant and diverse numbers of species rather than just a few. …