Semi-natural grasslands in the Ryukyu Islands were re-examined phytosociologically. As a result, four associations were classified: Thelyptero-Miscanthetum sinensis, Paspalo-Imperatetum cylindricae, Bidenti minoris-Imperatetum cylindricae and Euphorbio-Zoysietum tenuifoliae. These associations were contained in three alliances: Lygodio-Miscanthion sinensis, Imperation cylindricae and Zoysion tenuifoliae. Bidenti minoris-Imperatetum cylindricae is a new association differentiated by the presence of Bidens pilosa var. minor, Polygala paniculata, Centaurium floribundum, etc. This association develops at construction sites subject to weeding in urban areas such as slopes alongside expressways, open space of airfields, etc., and it is characterized by high ratios of therophytes, naturalized plants, species belonging to Artemisietea principis and Chenopodietea, and low ratios of hemicryptophytes and species belonging to Miscanthetea sinensis. These ecological characteristics are similar to those of Erigeronto-Imperatetum cylindricae which is maintained at construction sites subject to weeding from Tohoku to Kyushu district. Bidenti minoris-Imperatetum cylindricae seems to be an association in the Ryukyu Islands which corresponds to Erigeronto-Imperatetum cylindricae. Thelyptero-Miscanthetum sinensis was divided into two lower units dependent on the management. The Typical lower unit under abandonment of management is taller in vegetation height and lower in species richness than the Dianella ensifolia lower unit under traditional management. It was clarified that recent changes of environmental conditions in the Ryukyu Islands, such as weeding at construction sites, abandonment of management on traditional grassland communities, etc., have led to the appearance of a new association as well as simplification of the floristic composition. Furthermore, traditional semi-natural grasslands are rapidly decreasing in area due not only to the abandonment of management but also to grassland improvement, etc. From the standpoint of conservation of biodiversity, it was indicated that more detailed studies of actual conditions and conservation measures are immediately necessary in semi-natural grasslands of the Ryukyu Islands.

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Relationships between ground disturbance and forest floor vegetation were investigated in Fraxinus platypoda-Pterocarya rhoifolia forest along Ooyamazawa valley in Chichibu, Kanto District, Japan. Six landform types were distinguished along the valley investigated: terrace of debris flow, alluvial fan, scarp of terrace, new landslide site, old landslide slope and talus. Three major species groups were classified by cluster analysis of a releve data set. One of these was characterized by spring ephemerals, storage rhizome and anti-vegetative reproduction. This species group represented the forest floor vegetation inhabiting stable landforms such as terrace of debris flow and alluvial fan. The other two species groups characteristically included annual plants and those with replacement rhizome type. These were peculiar to the landforms scarp of terrace, new landslide site, old landslide slope and talus, located at the foot of sideslopes. In particular, scarp of terrace and new landslide site were extreme in having both the most unstable landform characteristics and floral features.

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Emergence, survival and establishment of elm seedlings (Ulmus davidiana Planch. var. japonica (Rehder) Nakai) along with coexisting ash (Fraxinus mandshurica Rupr. var. japonica Maxim) were investigated in relation to environmental traits, and the role of fluvial disturbance in their establishment on a flood plain was examined along the Azusa River in Kamikochi, central Japan. Elm seedlings emerged across a wide range of environment and disturbance regimes, while ash seedlings did not occur in arid sites with strong sunlight and coarse deposits. Seedlings disappeared within a year at undisturbed stands, such as elm forest with a thick herb layer. Elm seedlings were also washed away by flood, or died because of dryness on sandbars. Seedlings survived only at the sites with a thin herb layer such as newly abandoned channels in mature elm forest and young willow forest. The occurrence of elm saplings was mostly restricted to willow forest and alder forest, while ash seedlings occurred in partly disturbed elm forest in addition to the forests mentioned above. In willow and alder forest, saplings of elm and ash species were 10-30 years younger than the canopy species. This fact suggested that both species did not directly inhabit bare land but pioneer forests. Saplings in willow forest were supported by sandy deposits, suggesting that the establishment of both species followed flood disturbance which brought sandy deposits and extensively destroyed the herb layer.

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The habitat differences for vascular plant species, particularly for forbs, between the Pacific Ocean side (POS) and the Sea of Japan side (SJS) were investigated in the Japanese beech (Fagus crenata) forest zone. Some of the beech forest communities contain many forb species in the herb layer. Distributions of these communities themselves are restricted in POS; however most of the constituent forb species or their varieties are distributed also in SJS. Thus, in SJS, we can expect that these forb species will be growing in some communities other than beech forest. The community floristic composition and the habitat of vascular plant species were surveyed using phytosociological methods and description of topographic condition (165 releves were collected in total). Four micro-landform units were distinguished, i.e. 1) gentle crest slope, 2) side slope, 3) valley and 4) side slope in a small valley. Releves were collected for each micro-landform unit and the habitat of vascular plant species was compared between POS and SJS. As a result of this comparison, eight species groups were distinguished from their habitat patterns. The habitat differences for vascular plant species were observed as a species group which grew on gentle crest slope and side slope in POS where beech forest are established, and grew only on valley and side slope in a small valley in SJS where beech forest are absent. These species groups contained many forb species. Consequently, absence of forbs in beech forest in SJS may not be caused by an absence of forbs in SJS, but by habitat shift of forbs from beech forest (gentle crest slope and side slope) to other habitats in SJS.

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