Fires of Life
As fire season approaches, many plants and animals await the flames' rejuvenating powers
- Doug Stewart
- Aug 01, 1994
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. (Of course, an arid or frigid place probably won't naturally support the same number of species as, say, a Florida forest.) And fire can be the key to maintaining that diversity.
"What most people know about fire is what they've learned from Smokey Bear and Bambi," says Don Despain, a research biologist for the National Biological Survey (NBS) in Wyoming. "Smokey Bear was not an ecologist-he was mostly interested in lumber." As for Bambi, the 1942 cartoon in which animals flee in terror as a wall of flame chases them, "Bambi was a fairy tale." Yes, animals avoid fire, but there is no evidence they run for their lives to avoid being engulfed. For one thing, that's not how most fires burn; the massive but mostly slow-moving fires in Wyoming's Yellowstone National Park in 1988 burned for months.
Crews fighting forest fires have reported deer and elk darting away from a fire line, but the animals were probably fleeing the people, not the fire. Even the hottest flames rarely incinerate huge unbroken swaths of forest; rather, they leave a mosaic of burned patches-killing some plants and trees, scarring others, leaving many untouched, depending on variables such as vegetation, terrain and weather.
Like elk, most large mammals can easily sidestep such an approaching fire. Mice, rabbits and badgers, meanwhile, can wait it out in their burrows. (Soil is a superb insulator: when the surface of the ground is 2,000 degrees F, the soil 4 inches below may be no warmer than 100 degrees.) A bigger threat for small animals when they emerge is the sudden absence of the foliage and forest litter that once hid them from predators.
In fact, many plants and animals not only survive but thrive after a fire. The lodgepole pines of the western United States are sometimes called a "fire species" because they depend on regular fires to propagate. Intense heat speeds the release of their seeds by melting a resin that can hold their cones shut for decades. In some of the dry western states, moreover, deadwood piles up year after year without rotting. Periodic ground fires dispose of this accumulating tinder without harming the thick-barked trees, and this lessens the risk that the litter will eventually fuel "crown fires." These are unusually hot and fast-moving burns that can engulf entire trees in flames, killing whole stands of trees at once.
Knowing the importance of fire in regeneration, the National Park Service quietly adopted a policy in the early 1970s of letting natural fires burn themselves out, within limits. The policy drew criticism in 1988 when fires swept parts of Yellowstone. The criticism was worsened by press coverage of the fires that was itself overheated. "Sea of Fire Engulfs Once-Splendid Park," screamed The Milwaukee Journal in a typical headline. Governor Thomas Kean of New Jersey announced he was rushing 1,000 evergreen seedlings to the supposedly devastated park.
As it happened, no reseeding was necessary. To the contrary, the fire rejuvenated the forests, as cooler heads knew it would. Measuring the "seed rain" dropped by trees in several areas after the fires passed through, the NBS's Despain came up with 50,000 to 1,000,000 seeds per acre. "The system is well-adjusted to fires," he says. "All those forests are still there. Some of them are just in a different stage of development." As for wildlife, he says, very few animals died.
According to surveys after the fires, no grizzlies were killed, only one black bear and a handful of hoofed animals other than elk. About 300 elk did die of smoke inhalation, but that number is barely one-tenth the normal winter die-off for Yellowstone's huge elk herds. (Similarly, it's often said that the droughts that lead to fires end up killing far more animals than the fires do.) In all, says Despain, the most seriously affected animal population was probably the park's pinecone-eating red squirrels, which lost some of their food to fire.
In wilderness parks and other remote public areas, land managers can let natural wildfires burn. But in places where the native biota share their habitat with an influx of homeowners, as in the chaparral country of coastal Southern California, there's no such choice: Wildfires must be fought. In chaparral country, or Mediterranean scrub forest, summers are long, hot and dry. Dense thickets of oily-leaved plants like chamise are almost explosively flammable, and fires have swept through the area perhaps every 8 or 10 years for centuries. Last fall, wind-fanned fires in the mountains east and west of Los Angeles, many of them apparently set by arsonists, destroyed dozens of homes and left many of the hillsides as black as a charcoal briquette and seemingly as lifeless.
Especially hard-hit were parts of the Santa Monica National Recreation Area, which encompasses large amounts of privately owned land as well as wilderness areas. After one fire, says ranger Jacquie Stiver, visitors thought the area looked "blown up." But, she says, "Within a week, there were already green shoots-a week!"
After two months, Stiver and her colleagues counted 35 plant species growing on the blackened hillsides. Local fire species such as laurel sumac, purple needlegrass and coast goldenbush don't even need rain to resprout from their unburned roots. Seeds lying just underground are, like roots, largely unscathed by fire; mice, rabbits and quail emerge to feed on them while the terrain is still smoking. Local raptors like golden eagles, red-shouldered hawks and great horned owls swoop in to dine on the seed-eaters.
In the long term, as in other environments, fire helps restore diversity to chaparral country. "Without fire, large woody chaparral shrubs become dominant," says Ray Sauvajot, an ecologist at the federal Santa Monica Recreation Area. "When fire comes through, the landscape opens up incredibly. A lot of plants that couldn't germinate before because of competition from other plants, lack of light and lack of water, do so after a fire." From two to five years after a fire, herbaceous or nonwoody plants enjoy a revival, "which provides a tremendous food source for deer and other herbivores," says Sauvajot. Further up the food chain, bobcats and coyotes profit in turn.
Many local homeowners understandably don't view conflagrations such as last fall's in terms of ecological benefit. A particularly shrill debate has erupted over an endangered rodent, the Stephens' kangaroo rat. Property owners in much of Riverside County are enjoined from disturbing the animal's habitat of Mediterranean grassland-notably from cutting firebreaks around their dwellings with tractor-drawn, ground-chewing discs that slice through the rodents' burrows. Mowing flammable vegetation is fine, but mowing is more laborious, so many homeowners prefer discing. As a result, many did neither, and some homes went up in flames. "I'm now homeless, and it all began with a little rat," one resident complained in The Los Angeles Times last November.
Local wildlife managers and environmentalists dispute the idea that fires can be blamed on the kangaroo rats. "If every kangaroo rat in this area were destroyed tomorrow, the fires would still come," points out Anne Dennis of the local Sierra Club chapter. Not only that, fire officials say most of the fires were so intense that neither fire breaks nor firefighters could have stopped them. U.S. Interior Secretary Bruce Babbitt, among others, has suggested that people flocking to build in this arid region need to understand the risks they take living in a fire-prone landscape-a landscape that fire ecologist Richard Minnich of the University of California-Riverside has likened to a "lake of gasoline."
By contrast, when fire crackles through the western Virginia habitat of a rare plant known as Peter's Mountain mallow, hardly anyone notices-other than ecologists who set the fires. The plant grows on a rocky mountainside in a preserve owned by the nonprofit Nature Conservancy. A pink-blossomed perennial related to the hollyhock, Peter's Mountain mallow (Ilamma corei) was discovered in 1927, when some 50 plants were counted. "By 1980, there were four," says Caren Caljouw of Virginia's Department of Conservation and Recreation. "By the early 1990s, those same four plants were just hanging on." Heavy grazing by deer and feral goats had taken a toll, but even with these animals fenced out, the plants continued to decline. Then researchers in 1988 discovered that the site's soil was embedded with mallow seeds. Unlike most seeds, these "will not germinate unless the hard seed coat is cracked," says Caljouw. Only then can moisture reach the seed itself. "And the most natural way for the seed coat to crack is for fire to pass over the seed bed."
Until the 1940s, the site had been swept by wildfires every 7 to 10 years, but fire suppression turned the Peter's Mountain mallow seeds into popcorn without a popper. Then test plots were burned over in 1992, and soon after, ecologists discovered 14 seedlings poking up from the ash. A hotter burn last year, followed this time around by three weeks of rain, thrilled the scientists by producing 500 more seedlings. The moral of the story, according to Caljouw, is that "we can't just lock these places up if we want to protect them."
Not long ago, Don Despain of the National Biological Survey was studying a poster of Smokey Bear featuring wildflowers. He recalls, "I thought, 'Good grief, at least half of those species do better after a fire.'"
Massachusetts journalist Doug Stewart, a regular contributor, wrote about ladybugs in the June-July issue.