The Grassland Biome

The Grassland biome is dominated by grasses of a variety of species, all having adapted to the summer drought common to their semiarid habitat. The broad expanse of the grasslands is occasionally broken by stands of trees. The midlatitude grasslands of have been exploited more than any other biome by humans. Ninety nine percent of the United State's tall grass prairie and 70 percent of the mixed grass and short grass in some states have disappeared. Eight-five percent of the state of Iowa was once covered in native prairie, only one percent is left. The grasslands, especially the tall grass prairies are the world's most productive agricultural areas. The famous corn belt of the United States was created on top of the rich brown mollisol soils that developed beneath the surface.

The Prairies

Prairies are found on the humid side of the grassland biome and are often referred to as the tall-grass prairie. A favorable annual moisture balance supports a dense ground cover of tall grasses. Grasses range in height between .6 to 1.2 meters (2 to 4 ft.), with some as tall as 8 feet or more on the eastern margin of the prairies in the United States. In the tall-grass prairie of Iowa, for example, typical grasses are big bluestem and little bluestem; a typical forb is black-eyed Susan. Trees and shrubs are generally limited to moist sites along stream channels or hill slopes facing away from the sun. The nutrient - rich soil beneath the grasslands drew farmers to these regions. Now, most natural tall-grass prairie has been replaced by agriculture. Extensive grasslands also occur in Argentina and the Ukraine.

Figure 12.37 Tall grass prairie once common to the eastern Great Plains of Kansas (Courtesy NRCS)

The native grasslands of the world support a diversity of animal life. In North America, large grazers like the bison roamed the grasslands until hunted to near extinction by settlers moving west.

Steppe Grassland

On the drier side of the grassland biome lies the steppe grasslands. Vegetation must cope mixed_tall_short_grass_prairie_NRCS.jpg (9558 bytes) with the summer soil moisture deficit common to the steppe climate in which this formation class is found. Here, tall grass prairie gives way to grasses smaller than a half meter (2 ft).

Figure 12.38 Mixed Tall and Short grass
prairie of the U.S. Great Plains.
(Courtesy NRCS)

Toward the drier portions the ground cover becomes sparse with patches of open ground found between clumps of grass. Overgrazing of the steppe vegetation leads to accelerated wind erosion and desertification.

The Kalahari Desert actually isn't a desert under present conditions, though it is covered with much sand. It is a fossil desert found in the tropical steppe biome. Parts receive over 250 mm of precipitation, enough to support a cover of vegetation. It is a fossil desert found in the steppe biome. It' name is derived from the tribal word Khalagari, Kgalagadi or Kalagare meaning "a waterless place" or the Tswana word Keir, meaning "the great thirst".

Watch: "Struggle" from Kalahari:The Great Thirstland
(Source: Nature - PBS)

pronghorn_NRCS.jpg (7999 bytes) Figure 12.39 Wild Pronghorn Antelope cross the short grass prairie of Wyoming.
(Courtesy NRCS)
Burrowing animals like ground squirrels, prairie dogs, pocket gophers are common in the steppe grasslands. Burrowing predators like the black footed ferret are considered an endangered species.

Fire and the grassland biome

Fires, especally those started by lightning, are a natural occurence of the grassland biome. Fire destroys invasive species that compete with grasses. Fire suppression and farmland conversion have severely disrupted grassland ecosystems. Resource mangers now use prescribed burning to restore the health of prairie grasslands.

Watch: Planet Earth: Controlled Fires Help Prairies Thrive
(Source: Discovery News)

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