Difference Between Grassland Criteria And Savanna Criteria
Prairies, pampas, steppes, and savannas are all grasslands. They account for about 25 percent of the land surface on Earth. This biome occurs on every continent except Antarctica. Grasslands usually can be found in the middle of the continents and in what is known as a rain shadow—the side of a mountain range on which rain is less likely to fall.
Because grasslands usually receive from 10 to 30 inches (25 to 75 centimeters) of precipitation per year, they are too moist to be a desert but too dry to be a forest. Grasslands typically have a wet and a dry season, extreme temperatures, drying winds, and prolonged droughts—all of which shape the plants and animals that live on them.
Grasslands developed over the past 30 million years as Earth’s climate became cooler and drier and as mountain ranges were pushed up, creating pockets of drier areas. As these new areas developed, new plants that could survive the extremes of life on the grasslands evolved.
Tropical and subtropical grasslands are known as savannas, although locally they may be called prairies, scrubs, chaparrals, pampas, or barrens. Compared to the open types of grasslands, savannas are more parklike, with deciduous trees and small evergreens widely spaced among the grasses and shrubs. Unlike temperate grasslands, savannas are hot year-round. Yet, like all grasslands, savannas are not quite a forest, but are too wet to be a desert. Forests generally change to savannas in areas that receive less than 40 inches (100 centimeters) of rain a year. However, if the conditions are right, savannas can sometimes develop in areas that are wetter. For instance, the savannas, or llanos, in Venezuela receive abundant precipitation, but only at certain times of the year.
Savannas are found most often in the middle latitudes of the world, generally where the winds dry out the land. They are also common on the lee side of mountain ranges—that is, the side protected from the wind—often adjacent to deserts or the more open grasslands of the steppe. Savannas can also develop on either side of a rain forest. In South America, the savannas occupy an area of land about five times the size of France. Savannas and grasslands together extend over approximately 65 percent of the African continent.