The relationship between stomatal conductance (Gs) and leaf moisture properties in response to diurnal changes in water vapor pressure deficit (VPD) was investigated using canopy cranes for nine forest canopy tree species in a Malaysian moist tropical rainforest. Diurnal variation in leaf moisture properties and Gs and meteorological data were measured to determine the relationship of Gs change to diurnal VPD change, and to assess the influence of wood anatomical characteristics on stomatal sensitivity to VPD. For all species, negative correlations between VPD around the leaf (VPDleaf) and Gs were obtained, with Gs responses in the VPDleaf range of 1.2-5.9 kPa. Species with larger mean vessel diameters showed greater responsiveness of Gs to VPDleaf, with stomata responding more quickly to small changes in VPDleaf. On the other hand, significant differences between species were obtained for relative water content at the leaf wilting point (RWCtlp) and water potential at the leaf wilting point (Ψtlp), but no correlation was found between these leaf water properties and stomatal responsiveness to VPDleaf. In conclusion, we hypothesize that diurnal VPDleaf changes are the major signal to stomatal regulation in the target tree species, and that trees with larger vessel diameters have higher stomatal responsiveness to diurnal VPDleaf changes, which allows them to maintain leaf water status in response to the changes in both diurnal solar radiation and VPD. We will include a discussion of future research on forest ecology in the forest canopy, including our recent work on 'photosynthesis under strong light'.