In a species-rich perhumid tropical rainforest of Central Sulawesi, Indonesia, we studied the hydraulic properties of eight representative tree species and searched for evidence that analyzing hydraulic patterns at the species level provides valuable information to understand the role of abiotic drivers and structural parameters in controlling plant water consumption.We investigated the relationship between xylem hydraulic properties and tree size with the aim to determine possible hydraulic plasticity in response to the vertical variation in environmental conditions in an otherwise constantly humid forest.We found leaf-specific (LSC) and sapwood-area specific (kS) hydraulic conductivity of twigs to significantly increase with tree height across species. The marked increase of LSC and kS with tree height was closely coupled with an increase in mean vessel diameters and this trend was consistent for both, stem and twig xylem. Rates of xylem sap flow (J) of all tree species were strongly positively related to atmospheric vapor pressure deficit (VPD) and radiation (R), when evaluated on a daily basis. However, J started to level off at VPD values of about 0.4 kPa in trees of all size classes. We therefore concluded that the stomatal response of tropical moist forest trees is very sensitive to changes in the atmospheric evaporative demand. The tallest-growing species of our study, the Fagaceae Castanopsis acuminatissima, had hydraulic features that were remarkably different from the other species. This species, which is abundant in the study area, showed significantly higher rates of J, and higher hydraulic efficiencies in the root-to-leaf flow path and larger xylem vessel sizes than the other co-occurring species. We assumed that this hydraulic adjustment of xylem vessel anatomy is of vital importance for maintaining a sufficient water supply to the canopy under the wet conditions prevailing in Central Sulawesi. We found a high hydraulic plasticity with variation in tree height. This may be a direct response to changes in ambient conditions along the microclimate gradient from the forest understory to the canopy top. Large trees might be more resistant against drought events in the short run. However, there is evidence that especially tall-growing trees might be more vulnerable to prolonged periods of drought.