First, although the landscape seemed uniformly obliterated, in fact, the fires left a mosaic of varying burn severities (severity measures the fire's effect on the biota). In some places, intense crown fires (defined) had burned out all ground cover and killed all above-ground vegetation. But elsewhere, less-intense ground fires (defined) left trees alive.

© NCSA, University of Illinois at Urbana-Champaign, The Board of Trustees and Industrial Partners.

And the patchwork of destruction allowed the forest to regenerate much faster than expected. "Even close to the center of the largest burn, there were areas that were relatively unburned, that served as sources of propagules,"(defined) says William Hargove, a research associate at Oak Ridge National Laboratory who also studied the fire.

Secondly, wildflowers and shrubs survived in unexpectedly great numbers. From the severely burned appearance, "we expected that seeds for wildflowers and shrubs would have to come in from the edges, and disperse across the large patches."

They survived, Turner says, because the soil only charred to an average depth of 2 centimeters, and never more than 6 centimeters. "A lot of plants sprouted from roots or rhizomes (defined), she says, and by 1990, wildflowers were quite abundant," producing a good crop of seeds for 1991. "Regeneration of these plants was very rapid, and it came from within the burned area," she says. "Even the really big fires leave a legacy of the plants that were there before the fire."

Third, the fires had surprisingly little impact on wildlife. Turner, an ecologist, studied survival among elk and bison in a sagebrush grassland in Yellowstone's northern sector. "We expected a lot of winter mortality, since this land is a winter grazing ground. But we found that fires accounted for only 6 to 10 percent of observed mortality. Most of it was due to normal winter weather."

		Update 15 JULY 1998. Ten years after the blazes, Yellowstone continues to rebound. "Mother nature is taking care of herself pretty well," ecologist Jay Anderson of Idaho State University told Science magazine (see "Yellowstone Rising Again..." in the bibliography). Fish and mammals survived the holocaust surprisingly well, and annual weeds covered most of the charred areas the next year. Today, lodgepole pines -- which dominated the park for 10,000 years -- are poking through the shrubs and weeds, indicating a return of the park's old ecosystem. One factor that could interfere with that return, however, is global warming, which, scientists warn, could affect the species composition in the park within decades. "The projected changes we are seeing [in computer modeling] are dramatic and astonishing," geographer Cathy Whitlock of the University of Oregon told Science. The wetter winters predicted under global warming could allow the entry of larch, scrub oak and other non-native trees. And even though more big fires can be expected (they were more common during previous warm periods), the National Park Service plans to continue letting natural fires burn in Yellowstone.

Summing up
As far as Yellowstone is concerned, Turner concludes, "Big fires are not detrimental to the system in any way. It's difficult for the human-wild land interaction, but from the perspective of plants and animals, fire is a normal event, well within their capacity to deal with." And that's just as well, since in 1988 "the fires that were put out were ones that would have gone out anyway." The large fires, on the other hand, finally burned themselves out in cooler, wetter autumn weather.

The natural fire regime in the Yellowstone area, Turner notes, includes a hot, crown fire "that replaces the whole forest and the cycle begins again about every 100 to 300 years."

Want to read a letter on how Native Americans used fire?

Another lesson of the 1988 Yellowstone fires? Existing forest-fire computer models didn't work too well. Any sign of improvement on that front?

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