Grasslands

Uploaded by msnarayana on Oct 14, 2012

Grasslands are areas where the vegetation is dominated by grasses and other herbaceous (non-woody) plants (forbs). However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica. In temperate latitudes, such as northwestern Europe and the Great Plains and California in North America, native grasslands are dominated by perennial bunch grass species, whereas in warmer climates annual species form a greater component of the vegetation.

Grasslands are found in most eco region of the Earth. For example there are five terrestrial eco region classifications (subdivisions) of the temperate grasslands, savannas, and shrublands biome ('ecosystem'), which is one of eight terrestrial ecozones of the Earth's surface.

Vegetation
Grassland vegetation can vary in height from very short, as in chalk where the vegetation may be less than 30 cm (12 in) high, to quite tall, as in the case of North American tall grass prairie, South American grasslands and African savanna. Woody plants, shrubs or trees, may occur on some grasslands - forming savannas, scrubby grassland or semi-wooded grassland, such as the African savannas or the Iberian dehesa. Such grasslands are sometimes referred to as wood-pasture or woodland. As flowering plants, grasses grow in great concentrations in climates where annual rainfall ranges between 500 and 900 mm (20 and 35 in).The root systems of perennial grasses and forbs form complex mats that hold the soil in place.

Evolution
The appearance of mountains in the western United States during the Miocene and Pliocene epochs, a period of some 25 million years, created a continental climate favorable to the evolution of grasslands. Existing forest biomes declined, and grasslands became much more widespread. Following the Pleistocene Ice Ages, grasslands expanded in range in the hotter, drier climates, and began to become the dominant land feature worldwide.

Climate
Natural grasslands primarily occur in regions that receive between 250 and 900 mm (9.8 and 35 in) of rain per year, as compared with deserts, which receive less than 250 mm (9.8 in) and tropical rainforests, which receive more than 2,000 mm (79 in). Anthropogenic grasslands often occur in much higher rainfall zones, as high as 200 cm (79 in) annual rainfall. Grassland can exist naturally in areas with higher rainfall when other factors prevent the growth of forests, such as in serpentine barrens, where minerals in the soil inhibit most plants from growing. Average daily temperatures range between -20 and 30 °C. Temperate grasslands have warm summers and cold winters with rain or some snow.

Biodiversity...