But recently I have become aware of the natural history of Illinois, which has long been called the Prairie State. This started as I was looking at one of my several books about the Chicago Aurora and Elgin Railroad, the electric interurban railway that operated between 1902 and 1957. I was surprised by an early aerial view of the trackage in Wheaton, which indicated that at the beginning of the 20th century there were very few trees in my home town. By the middle of the century, when I was growing up, trees were to be found everywhere, leading me to believe that DuPage County was once heavily forested. As it turns out, there had indeed been forests, but not when Europeans arrived in the early 19th century. By then it was prairie, consisting of tall grasses and an absence of trees. So how did the prairies supplant the ancient forests?
Many scholars believe that the prairies, far from being a pristine pre-human landscape, were created by the aboriginal inhabitants, who subjected much of the North American continent to periodic controlled burnings. According to Steve Pyne,
the modification of the American continent by fire at the hands of Asian immigrants [now called American Indians, Native Americans, or First Nations/People] was the result of repeated, controlled, surface burns on a cycle of one to three years, broken by occasional holocausts from escape fires and periodic conflagrations during times of drought. Even under ideal circumstances, accidents occurred: signal fires escaped and campfires spread, with the result that valuable range was untimely scorched, buffalo driven away, and villages threatened. Burned corpses on the prairie were far from rare. So extensive were the cumulative effects of these modifications that it may be said that the general consequence of the Indian occupation of the New World was to replace forested land with grassland or savannah, or, where the forest persisted, to open it up and free it from underbrush. Most of the impenetrable woods encountered by explorers were in bogs or swamps from which fire was excluded; naturally drained landscape was nearly everywhere burned. Conversely, almost wherever the European went, forests followed. The Great American Forest may be more a product of settlement than a victim of it (Pyne 1982: 79-80).
Following European settlement of these territories, the forests generally returned. According to William Denevan,
The thesis of prairies as fire induced, primarily by Indians, has its critics (Borchert 1950; Wedel 1957), but the recent review of the topic by Anderson (1990, 14), a biologist, concludes that most ecologists now believe that the eastern prairies "would have mostly disappeared if it had not been for the nearly annual burning of these grasslands by the North American Indians," during the last 5,000 years. A case in point is the nineteenth-century invasion of many grasslands by forests after fire had been suppressed in Wisconsin, Illinois, Kansas, Nebraska, and elsewhere (M. Williams 1989,46).
Perhaps then the forests that cover much of the upper midwest of the United States are of fairly recent vintage. A century after those old photographs were taken, my hometown of Wheaton is covered with a variety of trees, both deciduous and coniferous. Trees have a stately beauty that no other plant can match. They provide shade and food, as well as wood for homes and furniture. In the jewish and christian traditions they are symbolic of faithfulness and steadfastness (see, for example, Psalm 1). They are among the most long-lived of all living things. Whatever beauty the prairies may have had, it is difficult to imagine my homeland without its trees.