Sapium sebiferum, an alien tree species that originated in China, has been naturalized in many areas of Japan. We examined the ecological characteristics of S. sebiferum community and the causal factors for its establishment at deforested sites, which were formed by clear-cutting the Quercus phillyraeoides community, on the Awaji Island in Japan. We recorded the locations of escaped S. sebiferum individuals of ≥1-m height in a 4-ha sampling area; 1118 individuals were found at the deforested sites, but none were found at the neighboring sites covered by the Q. phillyraeoides community. The S. sebiferum community mostly developed within 100 m of mature S. sebiferum individuals that were planted as ornamental roadside trees. Major component species of the Q. phillyraeoides community (e.g., Q. phillyraeoides and Q. serrata) and native pioneer tree species (e.g., Mallotus japonicus and Aralia elata), which are strong competitors of S. sebiferum, were rare or absent at the deforested sites because of browsing by sika deer. This suggests that browsing on native plant species by sika deer, clear-cutting of the Q. phillyraeoides community, and the presence of seed sources of S. sebiferum in the vicinity of the deforested sites greatly contributed to the establishment of the S. sebiferum community. The S. sebiferum community was similar to the Q. phillyraeoides community with regard to soil depth, although soil erosion was clearly caused by sika deer in areas of bare ground at the deforested sites. The native plant species were much more abundant in the S. sebiferum community than in the native plant communities established at the deforested sites. The maximal height of escaped S. sebiferum individuals was 7.6 m, whereas that of planted S. sebiferum individuals was 19.0 m. For escaped S. sebiferum individuals, the height highly correlated with the stem diameter at breast height and the height growth rate did not show a decreasing trend. Thus, the S. sebiferum community is likely to continue growing and exist for a long period. This may pose various problems for the conservation of indigenous ecosystems.

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Community structures and dynamics of dominant species in the early stages of secondary succession were observed from spring in 7-year-old to autumn in 10-year-old using a permanent plot after clear-cut of a deciduous broad-leaved forest. Community structures were rapidly developed during the study period; 3.8 to 5.4 m for community height, 814 to 966 stems per 200 m^2 for stem density and 3.5 to 10.2 m^2 ha^<-1> for basal area (BA). Twenty-seven species appeared in the permanent plot. Main species of each life form, tree species (Betula ermanii), sub-tree (Prunus grayana) and shrub (Hydrangea paniculata), simultaneously emerged just after clear-cutting. The size (diameter at breast height and tree height) differences among the three species were small in 7-year-old. Stem density of P. grayana and H. paniculata was more than two times of B. ermanii, and thus the both species dominated in 7-year-old. On the other hand, relative growth rates of B. ermanii was significantly higher than those of P. grayana and H. paniculata (P<0.05), and thus, BA and tree height of B. ermanii increased greatly during the study period. Moreover, the stem mortality of H. paniculata was rather high during the study period, and BA of B. ermanii surpassed that of H. paniculata in 10-year-old. Thus the pioneer sub-tree or shrub species, which invaded through buried seeds or stump sprouts, predominated with high stem density soon after clear-cutting. After canopy closing, the dominant species was succeeded to tree species depending on the difference of growth rate.

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Species composition, layer structure, species richness and life form were studied on the lucidophyllous forests in Hachijo-jima Island and Mikura-jima Island, the Izu islands, Japan, in relation to land use factors such as burnt fields and production of charcoal. Based on the combined factors of geology, land use and dominant canopy trees, 94 forest stands were investigated in the natural Castanopsis sieboldii forests on Mikura-jima Island and Mt. Mihara-yama (I), the semi-natural Castanopsis sieboldii forests on Mt. Mihara-yama (II), the semi-natural Castanopsis sieboldii forests on lava flows on Mt. Hachijo-fuji (III) and the semi-natural Persea thunbergii forests on the original surface of scoria on Mt. Hachijo-fuji (IV). In two ordinations obtained by DCA, stands within the four types of forests were clearly differentiated. In species composition, they were confirmed by the phytosociological tabulation. Major differences in layer structure, species richness and life forms were observed between the natural forests (I) and semi-natural forests (II, III and IV). The semi-natural Persea thunbergii forests (IV) were coppice forests that developed on abandoned burnt fields of the original scoria surface in relatively recent years, whereas the semi-natural Castanopsis sieboldii forests (II and III) were coppice forests which developed on lava flows and erosional landform in ancient ages. The difference in dominant canopy tree, species composition and layer structure between the semi-natural Persea thunbergii forests (IV) and the semi-natural Castanopsis sieboldii forests (II and III) depended not only on the volcanic activity, but also on the land use factors.

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The relationships between plant community and tree establishment on the abandoned skislopes in the lowland of Hokkaido, northern Japan, were investigated to verify if Miscanthus sinensis community, an indicator community for tree regeneration on managing skislopes, is effective as the indicator even after skislope abandonment. Shade-intolerant trees, represented by Betula platyphylla var. japonica and Larix kaempferi, established well on M. sinensis community of which ground surface had the highest available light, but did less in the other communities classified by TWINSPAN. The highest available light should be derived from the lowest vegetation cover in M. sinensis community. Age - height relationships on trees on a skislope abandoned for 5 years showed that the trees steadily regenerated in the M. sinensis community after the skislope abandonment. In conclusion, M. sinensis community can be used as an indicator to predict tree regeneration after the skislope abandonment.

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Secondary lucidophyllous (evergreen broad-leaved) forests with different population densities of sika deer (Cervus nippon yakushimae) were investigated in lowland areas of Yakushima Island, Japan, to clarify the effects of deer feeding pressure on such forests and to evaluate the naturalness of these forests. The vegetation structure, species composition, and species richness of secondary forests with a low population density of deer (deer-scarce forests) were compared with those of the secondary forests with a high deer density (deer-abundant forests). The vegetation cover of the ground layer (approximately 2 m high) was significantly lower in the deer-abundant forests than in the deer-scarce forests. The species composition of the ground layer greatly differed between the deer-scarce and the deer-abundant forests; many species occurred less frequently in the latter. These findings indicate that deer feeding pressure can simplify the species composition in secondary lucidophyllous forests to a considerable extent. The ground-layer species richness (number of the component species of lucidophyllous forest per 100 m^2) was significantly lower in the deer-abundant forests than in the deer-scarce forests, and it was negatively correlated with deer density. Many species consisting of primeval lucidophyllous forests with a low population density of deer were found to be absent or rare in the deer-scarce forests. In addition, the species richness of the deer-scarce forests was much lower than that of the primeval forests. On the basis of these results, it was concluded that the naturalness of the secondary lucidophyllous forests in lowland areas of Yakushima Island is very poor, and that deer feeding pressure has a great negative impact on forest naturalness.

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