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Shifting cultivation in the Amazon Territory of Venezuela (case study No. 1) generally takes place following cutting of primary forest. Because population density is very low there is little pressure to cut secondary forests. Therefore, long fallows are possible, during which nutrient stocks appear to be replenished to the level of the predisturbance forest (case study No. 2).

Campa Indians in the humid Gran Pajonal of Amazonian Peru are presently converting some abandoned door-yard swidden to savanna. If burning is practised it is often because a low herbaceous cover is of more immediate use close to the home than is rank secondary forest growing on exhausted soils. Burning is facilitated if pyric weed species dominate the newly abandoned swidden. The annual burning of abandoned swidden results in retrogression beginning with a bracken (Pteridium aquilinum) dominated sere, passing through an Imperata brasiliensis dominated sere and ending in Andropogon spp. dominated fire-sub-climax grassland. In the light of current hypotheses on the origin of savannas, it is argued that all savannas in the Gran Pajonal are derived. It is recognized that savannas can be categorized as either natural or anthropogenic depending on whether edaphic, climatic, palaeoclimatic or cultural factors are most important in their origin. In view of the proposition expressed herein that cultural factors alone are sufficient to explain the origin of Gran Pajonal savannas, it is recommended that futu're studies in other South American savannas should not overlook the effects of the long and varied tenures of local Amerindian groups. This is particularly important where colonial influences on both Amerindian and environment have been strong. Only through a complete analysis of both the environmental and cultural histories of any savanna region can a realistic appraisal as to its origin be made.