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Prairie
Grassland is abiome, anarea ofland which is mostlygrasses, Also, there may be some trees and rivers. The herbivore animals are adapted to a diet mainly of grass.
Thegraminoids became widespread toward the end of theCretaceous period. The appearance of mountains in thewestern United States during theMiocene andPliocene epochs created a continental climate which was favourable to the evolution of grasslands. Animals which ate branches were replaced by animals which ate grass. Eating grass needs different teeth from eating branches.
About five million years ago in the Miocene, the grasslands grew. In the New World and Old World, forestbiomes declined: and grasslands became much more widespread.
Grassland vegetation can vary greatly in height. Thechalk grassland of southern England is quite short, often with small, delicate flowers.
Grass is quite tall in theMississippi "tallgrassprairie",[3] theSouth American grasslands and theAfricansavannas. This provides a degree of cover for the smaller animals, and so increases the number of species which can live there.
Woody plants, shrubs or trees, may occur on some grasslands.[4] The root systems of perennial grasses andforbs (herbaceous flowering plants) form complex mats that hold thesoil in place.
When shrubs and bushes can grow more and replace grass, this is calledwoody plant encroachment. This change may be harmful. It may make the number of plant species fewer. It allows less water to go into the ground and animals have less to eat. From that perspective, woody encroachment may be a form of land degradation.
But this is not always the case. Encroachment can lead to good changes in nature.[5]
The tallgrassprairie is anativeecosystem of the drainage basin of theMississippi. Retreatingglaciers droppedmoraine material about 10,000 years ago. Wind-droppedloess and organic matter accumulated. This made the soil. The prairie had the deepest level oftopsoil recorded anywhere. 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.[6]
Between 1800 and 1930, most of this natural environment was destroyed. Settlers transformed what they called "the Great American Desert" or "The Inland Sea" intofarmland. They replaced the old grasses with new ones, mostlywheat andmaize, grasses that are ecologically different from the original cereals. They replaced the bison with cattle, another kind ofbovine. About 40% of the world'smaize grows in the United States, mostly on land that formerly grew grass. The grazing pattern of European cattle, the near-extermination ofprairie 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, andsoil erosion lost soil.
Estimates differ of how much original tallgrass prairie survives. Perhaps less than 1% to 4%, mostly in "scattered remnants found in pioneer cemeteries, restoration projects, along highways and railroad rights-of-way, and on steep bluffs high above rivers".[8]
In many other parts of the world, the grasslands have little rain or long dry periods. There are few trees because of the low rainfall. Thorny trees calledacacias are one of a handful of trees that are able to grow in some African savannas.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.[2]
↑Chapman, Kim Alan, Adelheide Fischer, and Mary Ziegenhagen. 1998.Valley of Grass: tallgrass prairie and parkland of the Red River region. St. Cloud, MN: North Star Press.ISBN 978-0878391271
↑2.02.12.2Dinorah Pous (2010).Blue Planet. North America: McGrawHill. pp. 114 to 115.
↑Crosby, Cindy. 2017.The tallgrass prairie: an introduction. Evanston, IL: Northwestern University Press, 2017.ISBN 9780810135475
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