Natural History
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North
American Grasslands
Grasslands cover one
quarter of the earth's surface. All of the continents except Antarctica contain some type
of grassland. While all grasslands are dominated by grasses, grasslands in different
locations. vary considerably from one another.
In the United States, the
greatest stretch of grassland is the prairie, extending from the Appalachians in the East
to the Rocky Mountains in the West.
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Tallgrass
Prairie
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The
Midewin Site
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There are three types of prairie in North
America: tallgrass prairie, mixed prairie, and shortgrass prairie.
In the tallgrass prairie, which receives the most rainfall, the prairie grasses can be
over five feet high. Moving westward, the amount of annual precipitation decreases. The
tallgrass prairie transitions to mixed prairie, with grasses between two and four feet. In
the rain shadow of the Rocky Mountains, the shortgrass prairie (also known as the plains),
supports grasses that are less than two feet tall.
While the tallgrass, mixed, and shortgrass prairies contain
different plant communities, they do share some characteristics:
- They generally exist on flat or rolling terrain with soils
that are rich in organic matter, slightly alkaline, and very fertile.
- Precipitation (averaging between 10 and 39 inches annually)
is concentrated in peak periods, interspersed with drought. Great fluctuations in rainfall
may occur from year to year.
- Wind is an important factor in the climate.Water evaporates,
contributing to already arid conditions. Wind also contributes to the spread of wild
fires.
- Fire plays an important role in the grassland ecosystem.
Most trees are killed or weakened by fire, but grasses have adapted to survive it and many
even grow better after they have been burned.
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