For analyzing and interpreting forest dynamics at community and ecosystem levels, this paper introduces the eco-physiological model and gas exchange chamber. The model considered spatial distributions of light intensity and leaf area of different leaf layers within the tree crown on an individual tree basis. Diurnal and seasonal fluctuations of the transpiration rate from May to October 1989 in a standingFagus crenatatree were measured at intervals of two weeks. The equation variables were defined by multiplying the VPD by the square root of photon-flux density. Estimation of transpiration of a tree was done by multiplying the transpiration rate per unit area by the leaf area at different leaf layers and the light attenuation rate at the same layer. Total stand transpiration was estimated by summing up the transpiration of the trees. The total annual amount of stand transpiration was 3.200 tHiOlhz.The maximum value of mean diurnal transpiration was 2.5 mm in August; and those of May and October were only 1.5 mm. The use of the combinations of the model and gas exchange chamber interrelations helps clarify the unknown functions, productive structures, and relationships among the items within a forest community and its environment.