A grassland is an area of land that mostly contains grasses. There are wild grasses, and less trees. Several parts of the world have grasslands. Grasslands are found in Africa, North America, Central Asia, South America, and near the coasts of Australia. The largest grasslands are in East Africa. Grasslands with a few scattered trees are called savannas. Others are called prairies or steppes.
Little rain falls in a grassland biome. Between 25 and 75 cm of rain falls each year, which makes the weather in these savannas hot and sunny in the summer and cool in the winter months.
Vegetation[change | change source]
Grassland vegetation can vary greatly in height. The chalk grassland of southern England is quite short, often with small, delicate chalkland flowers.
Grass is quite tall in North American "tallgrass prairie", South American grasslands and African savannas. This provides a degree of cover for the smaller animals, and so it increases the number of species which can live there.
Woody plants, shrubs or trees, may occur on some grasslands.
As flowering plants and trees, 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.
Tallgrass in North America[change | change source]
The tallgrass prairie is the native ecosystem of North America before it was replaced by modern farming. Retreating glaciers dropped material about 10,000 years ago. Wind-dropped loess and organic matter accumulated. This made the soil. The prairie had the deepest level of topsoil recorded anywhere. Animals such as buffalo, elk, deer, and rabbits added nitrogen to the soil with their urine and feces. Prairie dogs dug tunnels that "aerated the soil and channeled water several feet below the surface". For 5,000 to 8,000 years, more than 240 million acres (970,000 km2) of prairie grasslands were a major feature of the landscape.
Between 1800 and 1930, most of it was destroyed. Settlers transformed what they called "the Great American Desert" or "The Inland Sea" into farmland. They replaced the old grasses with new ones, mostly wheat and maize. They replaced the bison with cattle, another kind of bovine. About 40% of the world's maize for example grows in the United States, mostly on land that formerly grew grass. The grazing pattern of European cattle, the near-extermination of prairie dogs, and the plowing and cultivation of the land, did the damage. Plowing cut tallgrass root systems and interrupted reproduction. Drainage changed the soil's water content, and soil erosion lost soil.
Estimates differ of how much original tallgrass prairie survives. Perhaps less than 1% mostly in "scattered remnants found in pioneer cemeteries, restoration projects, along highways and railroad rights-of-way, and on steep bluffs high above rivers", to 4%.
Plants and animals[change | change source]
There are few trees in the grassland because of the low rainfall. Thorny trees called acacias are one of a handful of trees that are able to grow here. Wildfires are common and destroy trees. The animals also prevent trees from growing as they eat the tender sprouts before they can develop into grown trees. Elephants are known to tear down grown-up trees and feed on their leaves, making trees even more scarce.
Grass can still grow because it survives the aridity and the trampling of the animals. This is why grasslands can feed the vast numbers of animals, from the mice, rats, and other small animals that eat the seeds and sprouts, to the large herds of animals.
References[change | change source]
- Dinorah Pous (2010). Blue Planet. North America: McGrawHill. pp. 114 to 115.
- University of California Museum of Paleontology Grasslands website. Ucmp.berkeley.edu. Retrieved on 2011-12-01.
- NASA Earth Observatory webpage. Earthobservatory.nasa.gov. Retrieved on 2011-12-01.
- Pam Graham: “Tallgrass prairie” ProQuest Discovery Guides http://www.csa.com/discoveryguides/discoveryguides-main.php Released November 2011.
- "Microbes Beneath the Surface". Science Today: California Academy of Sciences. http://www.calacademy.org/sciencetoday/microbes-beneath-the-surface/5512848/. Retrieved 26 September 2014.