Long before, the plains were bulldozed flat during four major glacial advances and retreats that left behind sands, nutrient-rich soils and rocks. Wide flat rivers drained the melting ice finally about 11,500 years ago, at which time the tall grasses arose. Shorter domesticated grasses and farmers' fields of corn, wheat and soybeans have since replaced the tall grasses.
To the north and south of the tall-grass region, there emerged extensive forests. A long-debated scientific question, the researchers noted, is why the tall-grass prairie only supported grass when the soil easily could have sprouted diverse forests. Numerous ecological and climate-related theories have been raised, disputed and discarded.
The newly acquired data -- housed at the Midwestern Regional Climate Center at the State Water Survey -- are providing scientifically strong details, Changnon said.
One of the factors that emerged in the study was not new. The role of fire in sustaining the prairie and preventing the growth of trees was first established in the early 1950s, based on pioneer descriptions of deliberate actions taken by Indians in pursuit of buffalo. The impact and frequency of fire, however, are now strengthened by the new data on thunderstorms. The plains average 60 to 80 storms and more than 10,000 minutes of storm activity each year. Only Florida and the Gulf Coast experience more. The tall grass region also faces a three-to-five-times greater risk of fire from lightning.
In addition to the heat and searing of fires, severe droughts struck the region in 15 percent of the almost 105 years covered by the study; adjacent forested regions to the east and west had droughts in less than 10 percent of the years, and areas to the north and south were struck by drought even less frequently.
While rainfall was of similar frequency during summers, cold-weather precipitation in the tall-grass plai
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Contact: Jim Barlow, Life Sciences Editor
jebarlow@uiuc.edu
217-333-5802
University of Illinois at Urbana-Champaign
18-Aug-2003