Dataset: Local hydrological conditions influence tree diversity and composition across the Amazon basin

Tree diversity and composition in Amazonia are 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 local
hydrological conditions), varying from saturated and poorly drained to
well-drained and potentially dry areas. While these conditions may be
expected to influence species distribution, the impacts of local
hydrological conditions on tree diversity and composition remain poorly
understood at the whole Amazon basin scale. Using a dataset of 443 1-ha
non-flooded forest plots distributed across the basin, we investigate how
local hydrological conditions influence 1) tree alpha diversity, 2) the
community-weighted wood density mean (CWM-wd) – a proxy for hydraulic
resistance, and 3) tree species composition. We find that the effect of
local hydrological conditions on tree diversity depends on climate, being
more evident in wetter forests, where diversity increases towards
locations with well-drained soils. CWM-wd increased toward better-drained
soils in Southern and Western Amazonia. Tree species composition changed
along local soil hydrological gradients in Central-Eastern, Western and
Southern Amazonia, and those changes were correlated with changes in the
mean wood density of plots. Our results suggest that local hydrological
gradients filter species, influencing the diversity and composition of
Amazonian forests. Overall, this study shows that the effect of local
hydrological conditions is pervasive, extending overwide Amazonian
regions, and reinforces the importance of accounting for local topography
and hydrology to better understand the likely response and resilience of
forests to increased frequency of extreme climate events and rising
temperatures.