. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. PRAIRIES Prairies developed and were maintained under the influence of three major abiotic factors: climate, grazing, and fire (Anderson 1982, 1991). Occurring primarily in the central part of North America, prairies are subject to extreme ranges of temperatures, with hot summers and cold winters. There are also great fluctuations of temperatures within growing seasons. Droughts are also characteris
. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. PRAIRIES Prairies developed and were maintained under the influence of three major abiotic factors: climate, grazing, and fire (Anderson 1982, 1991). Occurring primarily in the central part of North America, prairies are subject to extreme ranges of temperatures, with hot summers and cold winters. There are also great fluctuations of temperatures within growing seasons. Droughts are also characteristic of the climate in the prairie regions. These droughts may last only one or two months or continue for several years. Cyclic droughts also occur every 30 years or so. Before intervention by humans of European descent, wildfires occurred regularly in the prairie regions. Any given parcel of land probably burned once every one to five years. These fires moved rapidly across the prairie, and damaging heat from the fire did not penetrate the soil to any great extent. A considerable portion of the aboveground biomass of a prairie was consumed each year by the grazing of a. ] Annual GroMland JBunehgratt S'tpp* / p=| Northarn Mutd-grau E=3 ][[]JSh<ylgra»« Prairie ^jsautharn Mlitdgrau Pralrlt ^JToligraM Pralna v]0«i»rt GrOMlond jShruat and Gronlond Itraii and Groitland Figure I. Major grassland types of the United States, Canada, and Mexico (reprinted from Risser et al. 1981). wide range of browsing animals, such as bison, elk, deer, rabbits, and grasshoppers. Prairie plants are adapted to these stresses by largely being herbaceous perennials with underground storage/perennating structures, growing points slightly below ground level, and extensive, deep root systems. The three abiotic factors of climate, grazing, and fire are important to keep in mind when formulating management practices for today's prairie remnants. In later discussions, grazing is mentioned as being
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