Abstract
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.
