To elucidate the effect of canopy gap formation on mechanisms of production in the evergreen clonal plant bamboo, we investigated photosynthetic responses and change in culms density of Sasa senanensis after canopy disturbance by typhoon in secondary deciduous broadleaved forests. In our previous report, we showed that S. senanensis was less susceptible to photoinhibition caused by increased light intensities after gap formation by typhoons than two deciduous broadleaf woody plants. In this study, we measured photosynthetic properties and leaf characters in plants exposed to canopy gaps through the next year of gap formation, and examined the culms density for 4 years following the disturbance. The one-year-old leaves of S. senanensis under gaps demonstrated no increase in photosynthetic capacity in one year after gap formation, while the current leaves in gap plants of S. senanensis showed higher photosynthetic capacity than those in shade-grown plants. The number of leaves and culms rapidly increased in the second year after gap formation. These results suggest that the enhanced photosynthetic capacity of the current leaves of S. senanensis from the next year after gap formation would contribute to rapid increase in production of culms in S. senanensis under gaps.