Como as condições hidro-topográficas locais influenciam nos padrões de diversidade e composição arbórea nas florestas da bacia amazônica?

Abstract

Tree diversity and composition in Amazonia is known to be strongly determined by the water supplied by precipitation. Nevertheless, within the same climatic regime, water availability is modulated by local topography and soil characteristics (hereafter referred to as hydro-topographic conditions), varying from saturated and poorly drained to dry and well-drained areas. While these may be expected to influence species distribution. However, the impacts of hydro-topographic conditions on tree diversity and composition remain poorly understood, especially at the whole Amazon basin scale. Using a data set of 443 1-ha non-flooded forests plots distributed across the basin, we investigate how hydro-topographic conditions influence i) tree alpha diversity, ii) wood density, and iii) tree species composition. We find that the effect of hydro-topographic conditions on tree diversity depends on climate, being more evident in wetter forests, where diversity increases towards locations with well-drained soils. Wood density is influenced by hydro-topographic conditions, also increasing toward better drained soils. Tree species compositional response are more complicated, with consistent community convergence associated with conservative resource use traits in well-drained locations, but diverging among different geomorphological regions for poorly drained conditions. Our results suggest that local hydro-topographic gradients filter species, influencing the diversity and composition of Amazonian forests. Overall, this study shows that the effect of hydro-topographic conditions is pervasive, extending over wide Amazon regions, and reinforces the importance of accounting local topography and hydrology to better understand the likely response and resilience of forests to increased frequency of extreme climate events and rising temperatures.