Grasslands

Grasslands

Grasslands, which are biomes wet enough to avoid becoming deserts but too dry to support forests, are usually flat or rolling regions that receive an average 25 to 100 centimeters of rain a year.

Although large portions of the earth's grasslands have been turned into farmlands, a number of grasslands can still be found in various countries of the world. Because rains are seasonal, grassland plants have adapted to drought conditions. In lowland areas, roots may go as far as three meters (more than nine feet) below the surface to locate water. More often the grasses rely on a huge root system, and some grasses produce a network of subsurface stems, called rhizomes, that stay alive after the above-ground foliage has died. The complex food webs supported by grasslands contain larger populations of animals than any other terrestrial biome. Examples include the huge herds of zebra and wildebeests found in African grasslands. Many annual grasses and legumes, including wheat, barley, onions, and peas, originated in the Mediterranean grassland region known as the Fertile Crescent (between the Nile Vally and the Mesopotamian flood plain, in what is what is now Turkey), extending eastward from Greece.

Because of differences in rainfall patterns, the grasslands of various regions have distinct characteristics. But three main grassland types can be found. Shortgrass prairies experience strong winds, light and infrequent rainfall, and rapid evaporation. In the United States, the North American Great Plains, a shortgrass prairie east of the Rocky Mountains, was plowed to grow wheat, and was overgrazed, making it vulnerable to the drought, strong winds, and poor farming practices during the 1930s that transformed the prairie into a Dust Bowl. The region's original population of some 60 million bison, at one time the dominant large herbivore of the North American grasslands, was hunted to near extinction.

Tallgrass prairie, which once extended west across North America from the temperate deciduous forests, were mostly turned into farmland, though some of these grasslands can still be found, for instance, in eastern Kansas. These wetter grasslands abound with daisies, sunflowers, and other flowers, as well as legumes.

South America and Australia vary in their vegetation, depending on rainfall. Where rainfall is lowest, rapidly growing grasses dominate; where rainfall is greater, acacia and other shrubs grow in patches; where rainfall is highest, savannas shift into tropical woodlands with tall, coarse grasses, shrubs, and low trees. Grasses can grow from three to 12 feet high (0.9 2.7 meters). These subtropical grasslands experience a rainy summer period followed by a dry winter. In winter, the grasses wither. Africa possesses the largest savannas, home to wildebeests, zebras, Cape buffalo, impalas, and other herds of large ungulates (hoofed animals), which are preyed upon by lions and cheetahs. Scavengers, including vultures, jackals, and hyenas consume the remains.

In South Africa and Zimbabwe can be found the Veldt or Veld, the grassy plateaus that support potato and maize crops and large herds of cattle, in addition to industrial and mining centers. Veldt elevations range from approximately 500 to 6,000 feet (150¦1,830 meters). Another well-known grassland is the Pampas in southeastern South America, an area of approximately 300,000 square miles (777,000 square kilometers). The region extends from North Argentina into Uruguay. In the more humid East Pampa, corn and other crops are grown, while in the dry West Pampa livestock are raised. The Steppes are the temperate grasslands of Eurasia, extending from Southwest Siberia to the lower reaches of the Danube River. They include the wooded steppe, where rainfall is highest and deciduous trees grow; the tillable steppe, with productive agricultural land; and the semi desert non tillable steppe.

In recent years, ecologists have become concerned about the damage to grasslands. Overgrazing and changing grasslands into croplands can change weather patterns by, for instance, affecting how much sunlight is reflected or absorbed in a region. Ecologists point out that grasslands provide valuable ecosystem services, in addition to the economic value they furnish through the meat, milk, wool, leather, and other products produced in grasslands. By processing large amounts of carbon as soil organic matter, grasslands help maintain the composition of the atmosphere. Tilled grasslands release large amounts of carbon, an issue of growing concern as scientists try to assess the potential global warming impacts from increased concentrations of carbon dioxide in the atmosphere.