THE SAVANNA LANDSCAPES OF THE AMAZON BASIN.

The following hypothesis is presented and defended. Climate is a predisposing factor, not a determining factor. Climate, characterised as it is in many parts of the Amazon Basin by a distinctive dry season of up to seven months in length, as in the Rupununi-Rio Branco region, often makes the presence of tropical rain forest problematical and predisposes the environment towards the development of savanna vegetation. Low soil fertility and laterite are frequently considered as prime determinants of savanna vegetation but here they are considered as features associated with savanna landscapes, especially on senile, pediplaned surfaces. Ocassionally they may be resultant factors, as when the nutrient cycle is broken after the disappearance of forest cover. Fire, which is also frequently considered a prime determinant, is generally a maintaining factor, but in limited areas may be causal, in the sense that it is immediate in chronological terms. The stage of geomorphic evolution and the dominant geomorphic processes in the landscape are those factors which most directly influence the position and behaviour of the water table, the soil moisture regime, the soil nutrient cycle, the ecoclimates of the region and thus, the distribution of forest and savanna. Author