Apocynum venetum var. bashikurumon （H. Hara） H. Hara is a rare plant, which is sporadically distributed, mainly in the coastal areas of Niigata, Aomori, and Hokkaido Prefectures, Japan.　In order to record its habitat characteristics and vegetation types, we established 143 rectangular quadrats for conducting a vegetation survey in Niigata Prefecture.　Vegetation type classification revealed that A. venetum var. bashikurumon was frequently found in plant communities under severe environmental stresses （e.g., sparse grasslands on the soft rocky cliffs of weathered tuff） or moderate levels of natural （e.g., semi-stabilized areas of sand dunes） and anthropogenic disturbances （e.g., wind-exposed grasslands on embankment slopes in the backshore zone）.　The terrestrial parts of these communities generally occurred at low densities.　These parts, together with extensive clonal growth of A. venetum var. bashikurumon using its long rhizomes, might facilitate the relatively high coverage of this species even in such habitats.　These habitats are not rare in the coastal areas.　Further studies on the characteristics of this species are essential for clarifying the reasons underlying the rarity of this species.

The stand structure and spatial distribution of trees in a swamp and its surrounding forest of the Yatsugatake Ranges of central Japan were surveyed related to the overly humid soil condition.　Soil reduction has been caused by high ground-water level and small fluctuation.　The relationship between the spatial distribution of dominated species （Alnus japonica, Betula davurica, Malus toringo, and Quercus crispula） of the forest and soil condition such as underground water level and status of the soil reduction were examined.　Alnus japonica was distributed on the reduction soil and high ground-water level, while M. toringo was on the non-reduction soil. Betula davurica and Q. crispula were on the non-reduction soil with a low ground-water level.　The spatial relationships among those dominated species were almost exclusive, while the spatial relationships between B. davurica and Q. crispula was sympatric.　These results reflected different tolerances of the overly humid soil condition.　On the other hand, spatial relationship between B. davurica and M. toringo in small area was sympatric.　It seems to be due to coexistence based on difference of maximum tree height of the two species. These results suggested that the spatial distribution of the trees in this study site was regulated primarily by the existence of humid soil.　In addition, the importance of vertical structure for the spatial distribution of the trees was also suggested.

Kuchinoerabujima Island is a volcanic island in Japan.　Many areas of the island are covered by secondary evergreen broad-leaved forests.　The surface geology of these forests is mainly classified into the following two types: （1） lava flow, where many exposed rocks are found, and （2） tephra deposit, where no exposed rocks exist.　We examined the influence of the surface geology on the species composition and richness of these forests. Forty-one stands were classified into four stand groups by two-way indicator analysis; three of the stand groups were in lava flows, whereas the surface geology of the other stand group was tephra deposit.　The sample scores for the first axis obtained by detrended correspondence analysis were strongly significantly correlated with exposed rock cover.　Species richness （i.e., the number of species per 100 m²） was significantly higher in lava flows than in tephra deposits, which may indicate a positive association between species richness and abundant exposed rocks.　Based on these results, we concluded that surface geology significantly affects the species composition and richness of secondary evergreen broad-leaved forests on Kuchinoerabujima Island, and that lava flows play an important role in preserving the overall species richness of these forests.