Gap formations are essential events for forest regeneration. Growth response of seedlings to the light improvement varies between species, which is considered to promote biodiversity in forests. At a leaf level, photosynthesis capacity changes in response to the gap formations. The change can be achieved by acclimation of already expanded leaves or plasticity of newly expanding leaves, both of which have been reported to vary among species. Does the change in photosynthetic capacity actually contribute to the growth after gap formations? The answer is still unclear, although the growth response and photosynthetic response to the light improvement have been separately studied in many species. Therefore we created gaps by falling canopy trees in a cool-temperate deciduous forest and studied the contribution. 6 deciduous woody species were used, which belong to 3 different functional groups. The stimulation of relative growth rate (RGR) in 4 years after the gap formations was clearly explained by the plasticity of photosynthetic capacity (P_max) of newly expanded leaves. The enhancement of the RGR and P_max correlated with the 8 years mortality at control site, which suggests a trade-off between the gap-response capacity and the understory shade-tolerance.