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I set my first forest fire about four years ago, in an oak woods along the north branch of the Chicago River.

I did the incendiary deed with a drip torch, a fire-starting device that consists of a small tank topped by a handle and a long spout. You fill the tank with a mixture of gasoline and kerosene and touch a match to the tip of the spout. A small control knob lets you adjust the flame to the exact level you want. Then you just walk through the woods, carrying the tank with the flaming spout just grazing the top of the leaf litter. The flames form a trail that marks your passing.

I should explain that it was all perfectly legal. My fellow firebugs and I had a permit from the Cook County Forest Preserve District. The local fire department had been notified and was standing by, ready to come to our assistance if we needed help. (We didn't.)

Your next question might be: Why were we given a permit to burn? Hasn't anybody around here heard of Smokey the Bear? Hasn't anybody seen those poignant posters showing a teary Smokey cradling a slightly scorched fawn? Don't we realize that only we can prevent forest fires?

To answer these questions and to justify my fiery stroll through the woods, we need to look at both human and natural history. About 150 years ago, loggers began to attack the great north woods of Michigan, Wisconsin, and Minnesota. They started in lower Michigan, cutting the big white pines first and floating them down the Kalamazoo and the Muskegon to the sawmills.

They were interested only in the tall central trunks, so the branches and the tops of the pines were left on the ground in the woods. With the canopy removed, the bright sun could reach the forest floor, drying out these piles of slash--as loggers call this stuff--and incidentally spurring the growth of grasses and other plants that make excellent fuel.

When lightning or human actions provided a spark, these cutover lands practically exploded. There was no organized fire protection, and some of the biggest blazes destroyed hundreds of square miles. The Peshtigo fire of 1871--the same dry year that produced the Chicago fire--swept through parts of eight counties in northern Wisconsin and killed more than 800 people, far more than the number who died when this city burned.

By 1900, you could travel for miles through the former pine woods of northern Wisconsin and never see a tree bigger around than your thumb. The woods had become grasslands, and the fires were so frequent that the trees didn't have time to grow big enough to withstand them.

When the trees went, the local economy went with them. There were no jobs, and whole towns vanished. The logging companies moved on to the Pacific northwest. They stopped paying taxes on their cutover land in the midwest, and millions of acres reverted to public ownership.

It was at this point that government action became essential to heal the wounds left by private enterprise (sorry, all you Republicans, but that's the way it happened). The states and the federal government began reforestation efforts. Fire control was an essential part of those efforts, since it would do little good to plant seedlings if they were going to be immediately incinerated.

Today, of course, millions of acres of cutover land support thrifty young forests, although the fires have left their mark on the land. Burned hardwoods can resprout from their roots. Pines cannot. The loggers removed seed sources when they cut the pines, and the fires killed off the young trees. Large areas in the north that used to be pine forests are now almost exclusively covered with hardwoods.

I have related all this to show how a climate of opinion could develop that all fires are unalloyed evil--destructive events with no redeeming qualities. This attitude extended beyond the forests: 40 years ago, J.E. Weaver, the leading authority on North American prairies, was writing of prairie fires as cataclysms that needed to be controlled to sustain the grasslands.

The change in scientific opinion began on the prairies. Land managers learned that if you kept fires out of prairies, pretty soon you didn't have a prairie anymore. Here in Illinois, unburned prairies were invaded by cottonwoods and box elders and turned into woodlands. In the west, a lethal combination of overgrazing and fire suppression turned millions of acres of once-productive shortgrass prairie into mesquite thickets.

Further study began to show that many kinds of woodland depended on fires to sustain them. In northern Minnesota, for example, jack pines dominated large areas. Jack pine is an intolerant species, one that will not grow in the shade. Without fire, a jack pine forest can last for only one generation: As the old jack pines die off, they are replaced by spruces, firs, and other shade-tolerant species. But with a fire hitting every century or so, the ground is cleared and jack pine seedlings can thrive.

We don't have any jack pines in Illinois, but we do--or rather, we did--have oak woods and savannas. Most of these are long gone, but some have survived long enough to have been incorporated into our forest and nature preserves.

Ecologists studying the life of these preserves quickly discovered two major problems. One, the oaks were being invaded by alien species, especially European buckthorn. And two, the oaks were not reproducing. We have many wonderfully gnarled old oak trees in our forest preserves and in city parks and backyards around the Chicago area. Most of these big trees date from about 1830. They live a long time, but not forever. When they go, there will be few young oaks to replace them.

John Ebinger of Eastern Illinois University manages a nature preserve, called Baber Woods, in Edgar County on the eastern edge of central Illinois. Baber Woods is an old-growth oak-hickory grove that seems to be in the process of becoming a sugar maple grove. Sugar maple seedlings and saplings can survive in deep shade for many years. They don't grow much, but they do stay alive, and when the big old trees that shade them get blown down by a tornado or just die of old age, the maples can grow very rapidly until they reach the canopy of the forest. This is the process that seems to, be occurring at Baber Woods.

Ebinger looked up the original land surveys, done in the early 19th century, for Edgar County and two neighboring counties. The government surveyors used to use "witness trees" to mark the locations of section lines. By studying their reports, you can get at least an impressionistic look at what trees grew on the land at the time of the survey. Ebinger discovered that fewer than 1 percent of the witness trees were sugar maples, and these were almost entirely confined to steep slopes and river bottoms, places where the thin-barked maples would be protected from fire.

Last fall, with the permission of the Illinois Nature Preserves Commission, he burned a part of Baber Woods. He will do it again this fall and next year. Throughout this process, he will be studying the effects of these blazes, not only on the trees, but on herbs, insects, and other animals as well.

My own fire experience comes from Somme Woods and Miami Woods, Cook County forest preserves along the Chicago River's north branch. These woods feature huge old oaks whose spreading crowns reveal that they started their lives in the open, not closely hemmed in by other trees. A dense understory of box elder, green ash, and European buckthorn suggests that these species will eventually replace the oaks, if our intervention does not help the oaks reproduce.

For me, burning the woods was very educational. The words "forest fire" meant holocaust as far as I knew, and the blaze we ignited was really something of a disappointment. Tiny flames, seldom more than six inches high, crept through the leaf litter. This was a forest fire you could step across, and our hardest job was keeping it going.

I also learned that maple and ash and buckthorn leaves that have lain on the ground through the winter will not burn in spring. But oak leaves will. It is as if (and I want to emphasize as if ) the thick-barked oaks were protecting themselves by dropping these flammable leaves, leaves whose burning would destroy the oaks' principal competitors.

And the fires do destroy the invaders. flames only slightly larger than those produced by a Zippo will kill a buckthorn stem and leave a burr oak completely unscathed. We are hoping that opening up the forest floor in this way will produce another generation of oaks, and with them, generations of all the plants and animals whose home is the oak savanna.

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