Geography of grassland ecosystems

Abstract

Grasses and grasslands occur on all continents, from the equator to the poles, and. together with the grazing animals that coevolved with diem constitute the world's major food resources. 'Mankind has depended upon them for his existence ever since our remote ancestors ventured onto the savannas and began a new mode of existence (Stcbbim, 1981). Grasses seem to have emerged during the late Creta-ceous. and by early Miocene the grasslands probably assumed a prominent place in the earth's vegetation (de Wet. 1981). Within the last few thousand years, man has helped their spread to a very large extent, and today almost 25 per cent of the world's plant cover is composed of grasslands (Barnard, 1969); however, in recent years extensive areas of natural grasslands have been ploughed for raising crops. The literature on the grasslands is truly voluminous but conspicuously uneven across the continents. It is beyond the scope of this paper to review all the litera-ture. and it is also not possible to describe the grassland types and their distribution in detail. Our objective here is to collate the information on the origin of grasslands in different parts of the world and to present a general picture of the major grass-lands on each continent.