Grasslands, which are biomes wet enough to avoid becoming deserts but too dry to support forests, are usually flat or rolling regions that receive an average 25 to 100 centimeters of rain a year.

Although large portions of the earth's grasslands have been turned into farmlands, a number of grasslands can still be found in various countries of the world. Because rains are seasonal, grassland plants have adapted to drought conditions. In lowland areas, roots may go as far as three meters (more than nine feet) below the surface to locate water. More often the grasses rely on a huge root system, and some grasses produce a network of subsurface stems, called rhizomes, that stay alive after the above-ground foliage has died. The complex food webs supported by grasslands contain larger populations of animals than any other terrestrial biome. Examples include the huge herds of zebra and wildebeests found in...