Grasslands
Ecosystems in which grasses and grasslike plants such as sedges and rushes dominate the vegetation are termed grasslands. Grasslands occur on every continent except Antarctica. It is estimated that grasslands once covered as much as 25 to 40 percent of Earth's land surface, but much of this has been plowed and converted to crop production, such as corn, wheat, and soybeans. Prior to the European settlement of North America, the largest continuous grasslands in the United States stretched across the Great Plains from the Rocky Mountains and deserts of the southwestern states to the Mississippi River. Other extensive grasslands are (or were) found in Europe, South America, Asia, and Africa.
Grasslands can be broadly categorized as temperate or tropical. Temperate grasslands have cold winters and warm-to-hot summers and often have deep fertile soils. Surprisingly, plant growth in temperate grasslands is often nutrient limited because much of the soil nitrogen is stored in forms unavailable for plant uptake. These nutrients, however, are made available to plants when plowing disrupts the structure of the soil. The combination of high soil fertility and relatively gentle topography made grasslands ideal candidates for conversion to crop production. Grasslands in the Midwestern United States that receive the most rainfall (75 to 90 centimeters) and are the most productive are termed tallgrass prairies.
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