Three large regions of rainforest occur in the Amazon Basin, Equatorial Africa, and south and south-east Asia (Figure 2.1). Away from these areas, where rainfall decreases and becomes seasonal, the rainforest is replaced by tropical monsoon forest, tropical grassland with trees, a poorer type of tropical grassland and finally by semidesert scrubland. The vegetation outside the rainforest has been greatly destroyed, and survives only in protected or relatively inaccessible areas. In the mountains, the tropical rainforests are replaced altitudinally by mountain rainforests, subalpine forests, alpine forests, and finally, on ranges that rise beyond 3,500 m, a treeless vegetation community. Mangroves in suitable places protect the coastal environment.
Traditionally the inhabitants of the rainforest have been hunters and gatherers or shifting cultivators. In the latter type of livelihood, patches of the forest are cleared by cutting and burning, and crops such as yam, cassava (also called tapioca and manioc), bananas, sweet potato and fruit trees are planted. In spite of the luxuriance of the forest the soils are usually infertile, and are kept productive only by the continuous decomposition of the fallen leaves and branches. Once cleared, the productive capacity of the land decreases in a few years, weeds start to establish themselves, and the cleared plots are abandoned for newer patches. The old clearings are soon under a secondary growth of vegetation, which starts to replenish the soil with nutrients, thus permitting recultivation of the plots after a gap of years.
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