Storms, fires maintain balance of nature, scientists say In places where wildfire has become rare, half of native plants are gone


WASHINGTON -- When your woods are on fire, your home washed away, it's hard to see fire and flood as anything but calamities, but scientists see nature maintaining its ecological balance.

Let your gaze sweep across the planet, these scientists say, and the forces of nature become forces for good, causing far less harm than our attempts to bring them under control.

Two studies reported in recent issues of Science, the journal of the American Academy for the Advancement of Science, conclude that natural disasters help maintain nature's balance in places as different as the prairies of Wisconsin and the rivers of northern California. By putting out fires and controlling floods, the studies conclude, humans have caused the disappearance of some plants and animals.

The findings add to a mosaic of evidence showing that fire or floods are good for the long-term survival of many landscapes, including the Grand Canyon, the New Jersey pine barrens and Florida's Everglades. University of Minnesota ecologist David Tilman says a bigger lesson is emerging; that humans have gone astray in our efforts to preserve wildlife and wild places.

Instead of setting up small, carefully controlled Noah's arks where creatures can rest undisturbed, Tilman concludes, nature should be allowed to take its course across the biggest possible swath of the land.

Preservation efforts "may be misguided if they take too narrow a view," Tilman writes in a third piece in the same issue of Science. "A seemingly pristine river that has been dammed, or a forest or prairie remnant that is inadvertently protected from fire, is not being preserved."

Those are fighting words to millions of Americans who use the dams' electric power to run their businesses, who eat beef from cattle grazed on unburned grasslands, who build houses from trees that were cut for timber rather than being allowed to burn. And even the researchers concede that it's not possible to simply stand back and let nature rip, regardless of the effects on people.

But in many places "it's very feasible to do that, if you get the public involved," said University of Wisconsin botanist Thomas Givnish, a co-author of one Science study. "There just needs to be a bit of an education process."

Givnish worked with fellow botanist Mark K. Leach to measure changes in the Wisconsin's few surviving scraps of prairie. Less than one-tenth of 1 percent of the state's original prairie remains, most of it in country cemeteries or along railroad rights of way.

In the 1940s and 1950s, botanists catalogued more than 3,000 kinds of plants in the prairie patches. But today, the researchers found, roughly one-third of them have disappeared, and they think the lack of fire is a major culprit.

Fire unlocks natural fertilizers like nitrogen and burns away the tallest prairie plants. In their place grow tough, ground-hugging herbs and wildflowers that help make the nitrogen available for other kinds of plants. The result: a rich variety of growing things, providing food for an abundance of birds, butterflies and other creatures.

Charcoal layers in the soil show that before the land was cleared for farms and towns, fire burned through the grasses about once every three years, Givnish said. But as people settled the land, they brought the fires under control. Until the 1950s, sparks from coal-powered locomotives sometimes set the prairie remnants ablaze. But steam engines have long been obsolete, and the land now burns once every six years at most, according to Givnish.

In places where fire has become very rare, more than half the native plants are gone - the prairie fringed orchid,; the purple trumpets of downy gentian; prairie clover; shooting stars; and others.

The rate of losses is among the highest studied anywhere, Givnish said. "These are supposedly pristine remnants, and even they have lost a lot of species over the last five decades," he said. "It's another ill effect [of development] that people have overlooked."

An equally subtle series of changes has taken place in the riverbeds of California's Coast Range, conclude researchers Timothy Wootton, Michael Parker and Mary E. Power in their paper.

Under natural conditions, the rivers flooded yearly, and the floods set off a complicated chain of events that ultimately helped steelhead trout, the scientists found. The floods wiped out certain kinds of flies - the ones that make their homes under boulders on the river bottom, where the trout can't catch them.

But other types of flies avoided the tumult of rolling rocks and survived, even prospered once their competitors were gone. And as those insects boomed, they provided a feast for the trout.

By damming the rivers, the scientists say, humans have given a boost to insects that the trout cannot reach and have thereby made it tougher for the increasingly rare fish to survive.

The lessons drawn by ecologist Tilman: Nature almost always turns out to be more intricate, more delicately balanced than we expect; and human beings' disruption of "processes such as floods and fire has unexpected, cascading consequences on many species."

Botanist Givnish thinks people can learn to accommodate natural forces like fire, at least in some places some of the time. "What's required is involving the public," he said. "Most people don't want to kill the beauty in their own back yard. Given the chance to help preserve it, they would jump at the opportunity."

Pub Date: 9/22/96

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