A stomatal conductance model and a photosynthesis model were applied to field measurements of transpiration and photosynthesis of seven tree species growing in subtropical southern China. Parameter values of drought resistance and tolerance and biochemical assimilation capacity were obtained by means of nonlinear statistical regression, and were used to quantify species succession. The analysis indicated that the models adequately described the ecophysiological behavior of the trees under various environmental conditions. We found a general pattern of decreased drought resistance and tolerance, but increased biochemical assimilation capacity from pines to heliophilus broadleaf trees to mesophilus broadleaf trees. Succession was explained on the basis of these physiological characteristics together with positive feedbacks caused by changes in soil physical properties. The ecophysiological explanation of succession implies that: (1) fitness of a species for a particular succession stage at a particular location can be measured by stomatal behavior and biochemical assimilation capacity under local climate and soil conditions; (2) selection of species for a particular location at a particular succession stage can be guided by the parameter values provided in this study; and (3) succession may be accelerated by selecting trees with large root systems and large soil–root conductances that facilitate soil hydraulic redistribution of water.