<P> Grassland vegetation often remains dominant in a particular area usually due to grazing, cutting, or natural or manmade fires, all discouraging colonisation by and survival of tree and shrub seedlings . Some of the world's largest expanses of grassland are found in African savanna, and these are maintained by wild herbivores as well as by nomadic pastoralists and their cattle, sheep or goats . </P> <P> Grasslands may occur naturally or as the result of human activity . Grasslands created and maintained by human activity are called anthropogenic grasslands . Hunting peoples around the world often set regular fires to maintain and extend grasslands, and prevent fire - intolerant trees and shrubs from taking hold . The tallgrass prairies in the U.S. Midwest may have been extended eastward into Illinois, Indiana, and Ohio by human agency . Much grassland in northwest Europe developed after the Neolithic Period, when people gradually cleared the forest to create areas for raising their livestock . </P> <P> The professional study of grasslands falls under the category of rangeland management, which focuses on ecosystem services associated with the grass - dominated arid and semi-arid rangelands of the world . Rangelands account for an estimated 70% of the earth's landmass; thus, many cultures including those of the United States are indebted to the economics that the world's grasslands have to offer, from producing grazing animals, tourism, ecosystems services such as clean water and air, and energy extraction . </P> <P> Grassland types by Schimper (1898, 1903): </P>

Where are tropical grasslands located in the world