This study compared the species composition and distribution of the forest communities between Korea and western Japan using vegetation releve database. The study area included the eastern and southern Korean Peninsula, Is. Cheju, Is. Ulreung, northern Kyushu, and Is. Tsushima. Twenty-eight forest communities were classified by tabular comparison with the total of 1204 releves. The forest communities of Is. Ulreung, Korean Peninsula, and northern Kyushu contained many characteristic species, while those of Is. Cheju and Is. Tsushima had less number of characteristic species. In Is. Cheju, the forest communities had many common species with Korean Peninsula in high elevation area, and with northern Kyushu in the low elevation area. Northern Kyushu and Is. Tsushima shared the highest number of common species. The physiognomical features of the vertical vegetation zones in the study area were similar, however, dominant species and species composition were different between the regions. In the lowland zone of the study area, the forest communities dominated by Castanopsis cuspidata var. sieboldii or C. cuspidata var. cuspidata were distributed except for northern part of the Korean Peninsula and Is. Ulreung. Additionally, Persea thunbergii forest was distributed widely in the lowest part of the study area, however, it showed the simplification of the species composition in the Korean Peninsula and Is. Ulreung. In the hilly zone, evergreen forest dominated by Abies firma and Quercus acuta established in northern Kyushu and Is. Tsushima, but they were absent in the Korean Peninsula. The difference in forest community was conspicuous, especially in the montane zone. In the Korean Peninsula and Is. Cheju, deciduous broadleaved forests dominated by two Quercus species (Q. mongolica and Q. serrata) flourished in the montane zone. In addition, the Abies nephrolepis forest was established in the same altitudinal range of the Q. mongolica zone in the Korean Peninsula. On the other hand, the forest communities of the montane zone in Is. Ulreng and northern Kyushu were dominated by two different Fagus species, i.e., F. multinervis and F. crenata, respectively. As a result of DCA ordination, evergreen broadleaved forests of the whole study area showed the lower scores along the first axis, while deciduous and coniferous forests in the Korean Peninsula showed the higher scores. The forest communities of Is. Cheju, northern Kyushu, and Is. Tsushima were located in the middle. The first axis reflected the gradient from oceanic climate to continental one. Evergreen broadleaved forests of lower elevation had higher floristic similarity, except for Is. Ulreung. On the other hand, deciduous broadleaved forests and coniferous forests of higher elevation had distinct characteristic species, thus less similar amongst each other and regional differentiation of forest community is progressing.

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Community structure and forest dynamics in a coniferous forest on Aokigahara lava flow, Mt. Fuji, were studied using a permanent quadrat of 0.25ha. Chamaecyparis obtusa (45.4% of basal area) and Tsuga sieboldii (26.3%) predominated in the canopy layer with stem density of 968 and 292ha^<-1>, respectively. Both species had typical inverse-J type DBH distribution. Twenty five sub-quadrats (each 100m^2) were divided into two groups by TWINSPAN: Tsuga patch and deciduous patch. Almost all T. sieboldii larger than 20cm DBH were distributed in the Tsuga patch. C. obtusa was distributed in both patches, but larger size of C. obtusa tended to be distributed in the Tsuga patch. Deciduous trees (e.g., Betula grossa and Prunus maximowiczii) with small size of T. sieboldii and C. obtusa were distributed in the deciduous patch. Moreover, the deciduous patch had rather light forest floor in winter and spring and had many seedlings of T. sieboldii and C. obtusa compared to the Tsuga patch. In the Tsuga patch, T. sieboldii was older and had lower relative growth rate of diameter (RGRD) than C. obtusa. There were few seedlings and saplings of T. sieboldii in the Tsuga patch, and thus the Tsuga patch would succeed from coniferous mixed forest to Chamaecyparis forest. On the other hand, Betula grossa, which had uniform age of 60-70yrs, had rather high RGRD compared to conifer trees in the deciduous patch. These forests might be pioneer deciduous patches within gaps in the Chamaecyparis forest. There were a lot of seedlings and saplings of coniferous trees, especially for C. obtusa, in the deciduous patch, and thus these patches succeed to Chamaecyparis forests. Some large and old trees of Quercus crispula were scattered in the permanent plot. Predominance of the coniferous trees with the exclusion of climax deciduous trees, such as Q. crispula, on the Aokigahara lava flow might be affected by human disturbance, such as using deciduous trees for charcoal within the forest.

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We investigated the flora and vegetation in 14 small catchments in the hilly Satoyama area in Tochigi Prefecture, central Japan, to objectively and quantitatively categorize their components, i.e., the vascular plants, into rarity types. The plants were categorized into eight rarity types on the basis of the combination of two divisions (above and below the median) with respect to the following three traits: (1) distributional range of species, which was represented by the number of occurring catchment, (2) habitat specificity, which was represented by the number of occurring community and (3) local abundance, which was represented by the average cover of species in the phytosociological releves. These categorization parameters were primarily determined on the basis of Rabinowitz's system of species rarity. The proportion of the species assigned to the rarest (rarity type VIII) or the commonest (rarity type I) category of the total number of species was higher than that of the other six categories. Although the proportion of species for each rarity type shows little variation among the sites (catchments), the index of rare species occurrence (IRO; total weighted proportion of rare species in each category) was higher in paddy fields and coppice communities than in other plant communities. Since effective conservation programs for species in question vary with their rarity conditions, our classification method of plants rarity based on the three above mentioned ecological traits enables us to identify the factors that may cause local extinction of species. Further, our study can serve as the first step in identifying endangered species and habitats; this knowledge may contribute to the conservation of plant species richness in local areas.

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Altitudinal zonation of forest vegetation and its causal factors in To-shima Island, Izu Islands, Japan were studied. The natural forest vegetation of the island was classified into Castanopsis-Persea type (C-P type) of the lowland and Eurya-Styrax type (E-S type) of the highland. As compared to the C-P type, the E-S type had the following characteristics: (1) the canopy represented by the mixture of evergreen broad-leaved trees (e.g. Eurya japonica, Persea thunbergii and Buxus microphylla var. japonica) and pioneer deciduous broad-leaved trees (e.g. Styrax japonica var. kotoensis and Zanthoxylum ailanthoides), (2) stand structure was immature state of development, and (3) its distributional core was the summit zone of the west slope. In addition, distributional area of E-S type in the west slope corresponded to the potential area of deciduous broad-leaved secondary forest in terms of mean temperature of the coldest month and cumulative monthly mean temperature during the winter bud season (from November to April). Moreover, the local wind estimated by the wind-shaped trees on the island corresponds to the seasonal wind direction in spring, summer and winter (west wind), That is, distributional area of E-S type corresponds to high wind area of west slope. These results indicated that E-S type is not a typical climax vegetation but a preclimax one that had strongly affected by natural disturbance, such as low temperature and wind stress.

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We investigated managed and abandoned vegetation on the levee slopes between paddy fields in order to clarify the relationship between the time since the last management and the species richness or species composition of semi-natural grasslands. The mean species richness per square meter in the managed grasslands was 25.3 and significantly higher than that in the abandoned grasslands. Species richness was significantly negatively correlated with the time since the last management. The negative correlation between cumulative cover and species richness was significant in layers below 0.6m. The composition of managed grasslands was similar to that of grasslands abandoned within the past 3 years but was different from that of grasslands abandoned for 4 years or more. The managed grasslands had 28 indicator species, while the abandoned grasslands had 1 indicator species. Competitive species such as Solidago altissima and Pleioblastus spp. gained height and cover in the abandoned grasslands within a few years. This increase is considered to be the reason for the decrease in the species richness and the change in the species composition.

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