Grassland covers more of the Earth's surface than any other type of terrain. Estimates range from 31 percent to 43 percent, depending on the definition of “grassland”, which can include savanna, prairie, scrub, high-altitude plains and Arctic tundra. More than 70 percent of some African countries are covered in grassland, and grassland makes up more than half the terrain in around 40 countries. One of the defining characteristics of grassland is that its vegetation is prevented from turning into forest by fire, grazing, lack of water or by freezing temperatures.
Grasslands support a wide range of wild animals, in particular birds. As well as providing year-round habitat for endemic bird species, grasslands also provide temporary refuge and breeding sites for migrating birds. They are therefore of vital importance, and their degradation in North America has resulted in a declining bird population since the mid-1960s.
Grasslands also provide grazing for domestic animals. In some areas of the world they have supported nomadic herds of sheep, goats and cattle for thousands of years. With growing human populations rearing ever more livestock, however, grasslands are at risk from over-grazing, which leads to soil erosion.
One of the major threats to grassland ecosystems is fragmentation by development, including roads. Breaking grassland up into small patches reduces its capacity to maintain biological diversity — it becomes degraded. This is what is happening in the Great Plains of the USA, where criss-crossing roads have fragmented 70 percent of the area into patches smaller than 386 square miles (1,000 square kilometers).
Much of the watershed areas of many of the world’s largest rivers are comprised of grassland. Here it performs the vital function of absorbing rainfall into underground aquifers that in turn feed into the river systems. Grasslands also act as “carbon sinks” by absorbing carbon dioxide from the atmosphere. They hold an estimated 33 percent of carbon stored in terrestrial ecosystems, most of which is to be found in the soil.
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