Abstract
Population structures of an understory shrub, L. umbellata were compared between two broad-leaved forests differed in stand age. The relative light intensity in shrub layer was lower in the 60-yr stand (15.2%) than that in the 15-yr stand (27.7%). The total basal area of stools was smaller in the 60-yr stand (3.04m^2ha^<-1>) than that in the 15-yr stand (4.90m^2ha^<-1>). These results suggest that the population biomass of stools decreases with stand age because the light irradiance level on the forest floor decreases with the development of tree stratification. From comparison of population structures between aerial stems and stools, it is suggested that the population of aerial stems of L. umbellata in both stands has been maintained by sprouting rather than seedling recruitment. However, in the 15-yr stand, the frequency distribution of stools was biased to the intermediate size-classes that ranged between 3-10cm^2 in basal area. This result suggests that these stools recruited intensively during a past period. Therefore, in the initiation stage of secondary succession after clearcuts, it is possible that seedling regeneration played an important role for the formation of the population of L. umbellata.
