Pequenas variações na fertilidade em solos oligotróficos melhor explicam a estrutura e composição florística em Campinaranas Florestadas na Amazônia Central

Abstract

Campinaranas are forests on oligotrophic white-sand soils in the Amazon, which are also frequently associated with flooding. These forests are characterized by high-dominance of few species, high endemism and much lower species richness than other Amazonian forests. Structural and floristic variation within Campinaranas at local scales vary greatly and edaphic factors, mainly fertility and flooding level variation, have been reported to affect the vegetation. Here we investigate the effects of edaphic variation on forest structure, diversity and composition of such forests at a site near Manaus, comparing the magnitude of the effects of soil fertility, soil toxicity, soil water retention capacity and variation in the level of the water table and flooding. We surveyed all trees with DBH ≥ 2.5 cm in 31 plots of 0.2ha. We found 6137 trees in these plots. Mean water table depth in the sampled plots varied from 30.5 to 144cm. Floristic composition, species richness, diversity were strongly affected by soil fertility and soil toxicity (Aluminium). Soil water retention capacity better explained variation in tree density among plots, but edaphic factors had no effect on forest height. Variation in the level of the water table and flooding had minor effects on vegetation structure and composition. Species diversity and richness were negatively correlated with soil fertility and the more fertile area had greater tree density and basal area. Results indicate that structural and floristic variation within white-sand Campinaranas are greatly influenced by minor variations in soil fertility and toxicity of oligotrophic soils.