The relationship between maximal stomatal conductance and leaf traits in eight Southeast Asian early successional tree species

The large-scale conversion of tropical old-growth forests to other land use types may subsequently increase the area covered by secondary forests. These tropical secondary forests are dominated by early successional tree species that may have elevated stomatal conductances and transpirational water loss. We studied eight abundant tree species of the tropical moist secondary forest in Sulawesi, Indonesia, for sun leaf stomatal conductance of water vapour (gsmax) in 4–7 m tall trees and related conductance to various leaf morphological (size, specific leaf area) and chemical parameters (nutrient contents, δ13C). gsmax showed a considerable variability among the eight coexisting early successional trees (393–734 mmol m−2 s−1). With a mean of 590 mmol m−2 s−1 it was more than twice as high as the maximal conductance reported for mature late-successional trees in tropical moist forests. Among the tested leaf traits, gsmax showed the closest relation to leaf nitrogen per area and leaf size; gsmax was only weakly correlated to leaf nitrogen per unit dry mass; no correlation existed with leaf δ13C values and specific leaf area. A significant negative relationship existed between gsmax and leaf size, which could point at a reduction in leaf-specific hydraulic conductance of the leaf petiole in large leaves of tropical pioneer trees. Thus, our data indicate that the early successional tree species studied in Sulawesi are characterized by a high but relatively heterogeneous water turn-over, and that leaf size might be a good predictor for maximal stomatal conductance.