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The Tallgrass Prairie
| Article
# : |
17762 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
6 / 1990 |
1,741 Words |
| Author
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Paul G. Risser
Paul G. Risser, president of Miami University in Oxford, Ohio,
is also chairman of the Committee to Improve the Science and
Technology Programs of the National Park Service. |
Imagine Illinois and Iowa with no corn and soybean fields. Or the adjacent states of Kansas and Oklahoma without wheat fields. What was there before the advent of farming? The tallgrass prairie.
Though about one-third of the plant cover of the world was originally grassland, the natural tallgrass prairies, with grasses two meters or more in height, were a unique subset of these grasslands. Tallgrass prairies are located in temperate regions where annual rainfall is more than 75 centimeters, but where there is a definite dry season during the year. This dry period discourages growth of trees and yet provides adequate soil moisture for vigorous growth by grasses and the associated nongrass species of the tallgrass prairie. Under these conditions, the plant canopy grows large, and perhaps more importantly, the root systems become very extensive and reach depths of two meters or more. As these roots die and decompose in the normal course of the plant's life, organic matter is deposited in the soil, adding humus and available nutrients. The resulting rich soils of Illinois, Iowa, Kansas, and Oklahoma were produced over centuries by these tallgrass prairies.
Most of these remarkable prairies have been converted into domesticated cropland comprising the North American breadbasket. The same conversions have occurred in Europe and the Soviet Union, and, to a lesser extent, in the pampas in South America and the fields in central and southern Africa. In North America, only about 10 percent of the original tallgrass prairie remains, and much of that is in the native rangelands of the Fling Hills and Osage Hills of eastern Kansas and the northeastern Oklahoma, where the Nature Conservancy has recently purchased 30,000 acres, the last expansive tract of virgin tallgrass left in the United States. Its acquisition is an initial purchase for a 50,000-acre tallgrass prairie reserve. A few other large tracts remain as preserves in Illinois, Minnesota, Missouri, Nebraska, and the Dakotas, with small preserves dotted around the region.
In North America, the tallgrass prairie is bounded on the east by the deciduous forest and the west by drier grasslands of the Central Plains. The eastern border is indistinct because in many areas the grassland transition to forest is as a savanna. These savannas have an open canopy consisting of relatively few trees and ground cover of typical grassland species. If the soil is shallow, resulting in slightly drier conditions, the savanna shifts to prairie. If the soil more coarse or subject to greater rainfall, the balance is shifted toward the
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