Ecophysiology of tropical dry evergreen forest, Thailand: measured and modelled stomatal conductance of Hopea ferrea, a dominant canopy emergent.
The diurnal variation in leaf stomatal conductance of 3 canopy emergent trees (Hopea ferrea) was measured on 13 days over a 6-wk period (August-September 1988) during the wet season in tropical dry evergreen dipterocarp forest, Sakaerat, Thailand, along with micrometeorological variables. Measured maximum stomatal conductances (g) were 510-343 mmol m-2 s-1. Diurnal variations of g were primarily controlled by incident radiation and soil water potential for the range of temperatures observed. During the measuring period, mean soil water potential (ψs) varied between -0.1 and -2.9 MPa. A multiplicative model was used to estimate the stomatal conductance from measurements of solar radiation (I), temperature (T), vapour pressure deficit (D) and soil water potential (ψs). Non-linear optimization of the g functions for I, T, D and ψs of the pooled normalized tree data set explained 84% of the variance, with I and ψs exerting the greatest effect on g. Optimization of the g functions for the individual tree data sets gave r2 values of 0.8-0.9. The optimized value of ψs that reduces g by 50% was found to be -1.2 (±0.07) MPa. The optimized response to D was small and negative. 5. The model can be used to predict the effects of changes in I, T, D and ψs on the g of tropical dry forests.