Species Spatial Distribution is Not Associated With Leaf Turgor Loss Point in an Aseasonal Wet Tropical Lowland Forest

ABSTRACT Drought tolerance inferred from functional traits has been shown to explain tree species distributions with respect to rainfall and topography in dry tropical forests, but the extent to which drought tolerance may influence species distributions in wet tropical forests remains unclear. We measured the leaf water potential at turgor loss point ( Ψ TLP ), a leaf hydraulic trait associated with drought tolerance, and representing the leaf water potential threshold for wilting, for 58 abundant tree species in an aseasonal lowland tropical forest in Peninsular Malaysia. We tested whether tree spatial distribution in relation to topographic soil moisture levels (i.e., Topographic Wetness Index; TWI) within a 50‐ha forest plot (the ForestGEO Pasoh plot) was related to Ψ TLP . We found that 76% of species showed spatial associations with TWI within the 50‐ha plot. Species' spatial association with soil moisture levels was statistically independent of Ψ TLP . Even in wet tropical forests defined by no distinct dry season, soil moisture associated with topography exerts a strong influence on tree species distributions, but topographic distributions are not associated with one of the components of species' drought tolerance as quantified with Ψ TLP . These findings highlight the sensitivity of tropical forests to variation in soil water levels, regardless of species' capacity to maintain physiological function under drier conditions, leading to a potential shift in community assemblages and structures following extreme events.