Age structure and dynamics of Cercidiphyllum japonicum sprouts based on growth ring analysis

We investigated the factors that encourage sprouting by Cercidiphyllum japonicum, as well as its ability to sprout after cutting, by analyzing the age structure, distribution, and growth of sprouts in one stool of this species. C. japonicum produced numerous sprouts in various age classes, ranging from 7 to 92 years old; the main stem was 226 years old. Sprouts that were relatively close in age (e.g., 30 or 80 years old) tended to form clusters. Based on an increase in the width of annual growth rings, we estimated that gap formation occurred about 30 years ago. This encouraged existing sprouts to grow more, and many sprouts were produced on the periphery of the stand to take advantage of the improved light conditions. After cutting, larger stems produced more simultaneous sprouts; therefore, sprout occurrence probably depends on the biomass of parent stems, although smaller stems were also able to produce some simultaneous sprouts. In the absence of physical damage, C. japonicum produced more sprouts as a function of increased age as a means of self-maintenance. C. japonicum sprouted simultaneously in response to external disturbances, such as gap formation and cutting, and it sprouted sequentially with increasing age. Therefore, although C. japonicum seedlings are rarely found in forests, C. japonicum can maintain its populations over long periods by sprouting, which compensates for sparse seedling regeneration.