Grasslands, referred to as prairies in the U. S. Midwest, pampas in South America, steppes in Central Eurasia and savannas in Africa, are relatively flat, continuous areas in which the dominant form of vegetation is grasses. This is because there is insufficient rainfall to support the growth of forests but enough to prevent deserts from forming. Depending on how they are defined, grasslands account for between 20 and 40 percent of the world's land area.
Although there are major differences among grasslands, including with regard to rainfall, temperature, and the species that live there, they can be classified broadly into temperate and tropical, with the former including those in North America, Argentina and Eurasia and the latter including sub-Saharan Africa and northern Australia. Rainfall can vary from season to season and from year to year, and temperatures can range from below freezing to above 32.2 degrees Celsius. The height of the grasses varies according the amount of rainfall, from about less than 0.3 meters to as high as 2.1 meters, and their roots can extend 0.9 to 1.8 meters into the soil.
In addition to hosting numerous species of animals and plants, grasslands play an important role in carbon storage because of their large biomass, both above and below ground, and because they are generally less vulnerable to fires than forests. Their great fertility, due to the combination of underground biomass and moderate rainfall, makes them highly appealing for agricultural use, and, in fact, much of the vast North American prairies have been converted to crop growing. Among the many other threats, both to the grasses and to the other species of plants and animals that live there are overgrazing, invasive species, urbanization, hunting and poaching, and climate change.