2021 Volume 38 Issue 2 Pages 133-145
Understanding how many species can coexist is major issue in ecology. We focused on Chrysosplenium L. (Saxifragaceae) species, which are small creeping plants that grow in mountain riparian forests where disturbances maintain the topography. Studies on species coexistence among phylogenetically related species can shed light on the mechanism of coexistence, because they have similar phylogenetically constrained traits, and niche differentiation, which is usually a major explanation in coexistence, is not a suitable explanation for the similar traits. We conducted vegetation surveys in 65 stands of mountain riparian forests in the upper part of the Watarase River basin, central Japan, and recorded environmental parameters. Coexistence and habitat preferences of Chrysosplenium species were analysed by phi coefficient and permutation tests. In the result, five Chrysosplenium species coexisted and showed similar habitat preferences. The five species tended to grow on topography formed and maintained by fluvial disturbances, where Fraxinus platypoda which was tree species in late stage of succession dominant. Our results illustrate the phylogenetic and ecological assemblages of Chrysosplenium species on the forest-stand scale (102-103 m2). On the other hand, Chrysosplenium macrostemon and C. pilosum var. sphaerospermum did not prefer to the forest that Pterocarya rhoifolia which was relatively pioneer species dominated on the topography although prefer to P. rhoifolia dominant forest established on which severe disturbances were absent for a long time. Therefore, a period of habitat stability might be important for these assemblages, especially until F. platypoda becomes dominant. Further, it was inferred that similar opportunities for migration and establishment as affected by various disturbances are important for their coexistence.
