Grasslands develop as a result of changes in climate, changes in plant communities, and fires.

Climatic Change

Grasslands first appeared millions of years ago after mountains formed and caused climates to change. In North America, for example, the Rocky Mountains blocked moist air traveling across the continent from the Pacific Ocean, making the middle part of the continent drier. This caused trees to die and be replaced by grasses, which could adapt to the drier climate. The same process happened on other continents, allowing grasslands to form in places such as central Asia and South America. Grasslands throughout the world were fairly well established about 5,000,000 years ago.

Succession

Grasslands also develop through a process called succession, a slow sequence of changes in a plant community. In dry areas, the growth of mosses and lichens (LY-kens) may be followed by the growth of leafy, nonwoody...