ABSTRACT
With the rapid growth of the world's population, most societies have been demanding much more from the Earth's resources and, therefore, affecting the land surface at ever-increasing rates. Prehistoric evidence shows that in Palaeolithic times the early hunter-gatherers used fire and, accidentally or intentionally, burned extensive areas of forest (Brain and Sillen 1988). The early agronomists burned large areas of land to create farmland or pasture, they modified the soil by ploughing, altered the drainage by irrigation, introduced or bred new animals and crops, and altered the natural vegetational structure of many regions (Harlan 1986, Davis 1987). In more recent times, humans have destroyed enormous tracts of natural vegetation, excavated large areas of land, greatly modified the landscape, and even created new land.
