Moso bamboo expansion to surrounding ecosystem has been noticed in east Asian countries. Our previous studies revealed larger stand transpiration than that of surrounding coniferous forests and that almost same amount of Moso bamboo stand transpiration regardless of culm density (i.e., 4,000–10,000 culms/ha). This suggest consideration of individual transpiration in stand is needed to understand the conservative stand transpiration. This study measured sap flux in five culm age groups (each age group contain 7-8 culms) in a Moso bamboo stand in central Taiwan.    
Older age culms showed lower sap flux than that of younger culms. In particular, oldest culms showed significantly lower sap flux than that of younger culms, probably due to lower stem hydraulic conductivity. The number of oldest culms accounted for 20% of total number of culms at this site. On the other hand, total amount of transpiration from older culms accounted only 5% of total stand transpiration at this site, suggesting increase of old culms e.g., in unmanaged stands does not accompany the increase of stand transpiration. Our study showed importance of culm age structure in Moso bamboo stand transpiration estimates.