Grasslands of the World

Grasslands are herbaceous dominated areas with very low abundance of trees and shrubs. They are found in areas with intermediate precipitation amounts (250–1000 mm) characterized by occasional droughts and are usually the most extensive in the interior of continents. Grasslands began to form 11–24 million years ago (MYA) when grasses invaded woodlands. Grasses initially all had C3 photosynthesis and were found in shaded conditions. However, grasses with C4 photosynthesis require full sun, and they increased in abundance during this time to achieve between 20–40 percent of the local vegetation. By around 6–8 MYA before present, C4 grasses were widespread on most continents that now have extensive grasslands. Grasslands can be classified by soil type or based on gradients of humidity-aridity and human impact (wild grasslands to improved pastures). African savanna grasslands are important because it is where Homo sapiens (humans) speciated and eventually spread to other continents.