Coexistence of Tree Canopy Species

The canopy tree species Fraxinus platypoda, Pterocarya rhoifolia, and Cercidiphyllum japonicum coexist at the Ooyamazawa riparian forest research site. In this chapter, we clarify the coexistence mechanisms of riparian tree species as they pertain to disturbance regimes, life-history strategies, and responses to environmental factors. Reproductive strategies, e.g., seed production and germination, differ widely among these three species and we observed probable reproductive trade-offs in each species. Canopy-height individuals of F. platypoda are recruited from advanced saplings, and P. rhoifolia and C. japonicum both established following large-scale disturbance events. Basal sprouting, i.e., vegetative reproduction, is likely the mechanism by which C. japonicum survives and attains co-dominance in riparian forests. F. platypoda had greater shade and water tolerance than the other two species. Each of these species is well-adapted to the various disturbances typical of riparian zones. Therefore, the coexistence mechanisms among them are likely a combination of random chance and niche partitioning.