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.

Decreases in grassland plant species richness due to modernized agriculture and land abandonment represent an important biodiversity conservation issue in rural Japan. Several studies have reported rapidly shrinking populations of grassland plants;however, few studies have explored the ecological traits shared by these species. In this study, we applied generalized linear mixed models to assess the relationships between occurrence and ecological traits and characteristics in common grassland plants found in rural landscapes of Kochi Prefecture, Japan. We established 15 line transects along paddy, upland field, and forest edges （length, 100 m） in 16 rural landscapes for a total of 240 transects, and surveyed the occurrence of 50 common grassland plants. For 45 of these 50 species, we identified seven ecological traits and characters:ruderality, stress tolerance, rooting system, growth habit （lianas or other）, maximum plant height, seed dispersal types （anemochory, barochory, or other）, and life type （dicotyledonous herbs or other）. Ruderality and stress tolerance were quantified in terms of leaf area, specific leaf area, and leaf dry matter content. Occurrence varied among the 50 grassland plants in the 240 transects. Miscanthus sinensis, Fallopia japonica var. japonica, and Geranium thunbergii were observed frequently, whereas Lysimachia clethroides, Potentilla fragarioides var. major, Phtheirospermum japonicum, and Leibnitzia anandria were rare. Of the seven ecological traits, barochory and squared stress tolerance had the highest variable importance, followed by maximum plant height;these variables were selected for the model with the smallest Akaike information criterion value. Occurrence probabilities for the 45 grassland plants decreased as stress tolerance increased and maximum plant height decreased, although those for barochory species were low. These results suggest that among the plant species assessed in this study, barochory species and shorter grassland plants with higher stress tolerance are likely to experience population and habitat decreases. Future studies should expand on the ranges of ecological traits and grassland plant species analyzed to better understand these decreases in grassland plant richness in rural Japan.

We conducted vegetation surveys of semi-natural grasslands, which were maintained by periodic mowing, on the levee slopes of traditional terraced paddy fields in Hyogo Prefecture to examine the regional differences in species composition and richness of such grasslands and to analyze the relationships between climatic conditions and those attributes. In this study, the area of the prefecture was divided into the northern region, southern region, and Awaji Island. A total of 382 grassland stands in the three regions were investigated. The species composition of the stands was analyzed using the phytosociological tabulation method. The stands were divided into three community types:A, B, and C. Types A and C were found only in the northern and southern regions, respectively. Type B was distributed mainly in the southern region and Awaji Island. The results of the detrended correspondence analysis （DCA） showed that the species composition differed among the three community types. Stand scores on the first DCA axis were strongly correlated with warmth index （WI） and maximum snow depth. The numbers of native species and perennial species per quadrat （1 m²） were significantly higher in type A than in types B and C. Such attributes of species richness were also correlated with WI and maximum snow depth. These results suggest that the species composition and richness of semi-natural grasslands were affected by climatic factors such as temperature and snowfall.

This study compared the species composition of Fagus crenata forests between Okushiri Island of southwestern Hokkaido and its surrounding area using vegetation relevés.　We investigated species composition in 17 forest stands on Okushiri Island, 10 on the Oshima Peninsula and 14 in the northern Tohoku region, and obtained 41 phytosociological relevés.　Further, 7 relevés from the Japan Sea side of the Tohoku region were extracted from the literature.　Two vegetation types were classified on Okushiri Island by the TWINSPAN method:type I （including two sub-types Ia and Ib） and II.　Moreover, two vegetation types, each with two respective sub-types （A1, A2, B1 and B2）, were obtained by the TWINSPAN method applied to all relevés.　Each type I or II stands on Okushiri Island included in sub-type A1 and B1 vegetation, respectively.　Type A1 was identified in 13 stands of Okushiri Island type I vegetation and 2 stands in the northern region of the Oshima Peninsula, and was characterized by the occurrence of Ilex rugosa var. rugosa, which occurs exclusively in beech forests in the northern region of the Oshima Peninsula.　Further, elements of boreal forests, such as Betula ermanii var. ermanii, Clintonia udensis and Dryopteris expansa, were present in Okushiri Island type I vegetation, which is a floristic feature of beech forests in the northern region of the Oshima Peninsula.　On the other hand, species with high occurrence in the Japan Sea side of Honshu including the northern Tohoku region, such as Dryopteris sabaei, Arachniodes mutica, Padus grayana and Mitchella undulata, were frequently found in type A1 vegetation, which is another feature of Okushiri Island’s beech forests.　The remaining vegetation type, B1, on Okushiri Island consisted of 4 stands on Okushiri Island and 6 in the southern region of the Oshima Peninsula and the northern Tohoku region.　This vegetation type was characterized by the presence of differential species for the association distributed over the southern region of the Oshima Peninsula, which has a short snow-cover period, such as Mianthemum dilatatum, Carex conica and/or Disporum smilacinum as well as type A1 vegetation.　Consequently, the beech forests on Okushiri Island showed diverse floristic features, despite its small size, common to those in the northern region of the Oshima Peninsula, those in the Japan Sea side of Honshu, and those in southern region of the Oshima Peninsula.

Vegetation and soil characteristics of two physiognomic types of young Pinus thunbergii-dominated stands, that is, naturally recovered type on beach ridge and sand dune （RS;five sites） and afforested type on artificial mounds （AS;four sites）, were compared along Sendai Bay after the Great East Japan Earthquake and Tsunami in 2011.　Of the 111 vascular plants found, 34 were found only in RS and 27 were found only in AS.　The percentages of perennials, annuals, alien species, and coastal species were 50.5%, 29.7%, 25.2%, and 9.9% of the total species, respectively.　Seven vegetation types were classified using modified TWINSPAN.　In the first division, 54 surveyed stands were divided into two groups:one group mainly contained AS stands indicated by alien species, while the other group mainly contained RS stands indicated by coastal species.　Stands of RS and AS were plotted along nMDS axis 1, which was correlated with vegetation cover and number of woody species.　Stands of RS were widely dispersed along nMDS axis 2, which was correlated with the number of coastal plant species.　Soil pH, water permeability, and electrical conductivity differed among the different stands （n = 20）, however, no significant difference was observed between RS and AS groups.　Weak correlations were found between total number of species and the particle diameter value of D20 and number of coastal species and electric conductivity.　AS with artificial mounds was poor in coastal and woody species except the planted pine saplings, probably owing to the absence of reproductive sources.　Laying coastal sand increased the number of coastal plants in AS on artificial mounding.　Therefore, artificial mounding and afforestation will have striking impacts on coastal vegetation. The impacts, however, may be mitigated by laying local sand containing propagules of coastal and woody species.