Farming system where farmers move on from one place to another when the land becomes exhausted. The most common form is slash-and-burn
agriculture: land is cleared by burning, so that crops can be grown. After a few years, soil fertility is reduced and the land is abandoned. A new area is cleared while the old land recovers its fertility.
Slash-and-burn is practised in many tropical forest areas, such as the Amazon region, where yams, cassava, and sweet potatoes can be grown. This system works well while population levels are low, but where there is overpopulation
, the old land will be reused before soil fertility has been restored. A variation of this system, found in parts of Africa, is rotational bush fallowing that involves a more permanent settlement and crop rotation.
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