WETLAND AND UPLAND FOREST ECOSYSTEMS IN PERUVIAN AMAZONIA - PLANT-SPECIES DIVERSITY IN THE LIGHT OF SOME GEOLOGICAL AND BOTANICAL EVIDENCE

Recent hypotheses have suggested fluvial disturbance resulting from long-term sub-Andean tectonics as a source of high species diversity in western Amazonia, a region presented as a mosaic of fossil and current floodplains produced by vast lateral river migrations. In such a system, wetland forests would be a center of high diversity. These hypotheses are discussed. On the one hand, an analysis of the differential tectonic effects of faulting and folding on the two western Amazonian morphostructural units clearly indicates that areas affected by fluvial dynamics are limited to well-defined depressions, the tendency of which is subsidence or entrenchment. Most uplands have not been affected by fluvial dynamics since the Pleistocene. On the other hand, botanical surveys show that the respective wetland and upland floras are very distinct, and that upland-forest species diversity is clearly greater than that of wetland forests. Several arguments suggest that the disturbance of forests on vast areas and severe ecological constraints (e.g., flooding) lead to reduced plant-species diversity. The great age and stability of upland forests, and the rather constant ecological conditions in the understory (including gap-phase regeneration) are still convincing explanations of their high species diversity. © 1990.