Flowering phenology of a duodichogamous self-incompatible tree species, Castanea crenata

Castanea crenata is a duodichogamous tree in which individual flowering phenology progresses in the order male → female → male. Differences in flowering patterns between individuals and the adaptive significance of duodichogamy in C. crenata have not been previously explored in natural populations. In this study, we monitored the phenology of individual male and female flowers from eight C. crenata trees in a natural forest using tree towers. In five of the eight trees, flowering occurred in the order male → female → male. For the other three trees, either type of flowers (i.e., first male, second male or female) started to bloom at the same time. Within individual trees, male and female phases overlapped. In addition, the flowering period of the first and second male phases was assessed for 49 trees. At this population level, we observed a greater overlap in male and female flowering periods after pooling the first and second male phases. This overlap in flowering periods among individuals was also evident when we included our eight study trees in the population data. Our results suggest that duodichogamous flowering phenology may promote outcrossing of the self-incompatible tree species C. crenata, rather than prevent self-pollination.