ON THE CHAMAECYPARIS OBTUSA FOREST IN SHIKOKU, SOUTHERN JAPAN

Abstract

As to the distribution of the Chamaecyparis obtusa forest in Japan, KAWADA explained it by the precipitation throughout the year. Afterwards, MAEDA pointed out that the monthly rainfall in winter indicating about 100mm or more is suitable to the occurrence of this forest. At the same time, he also stated that the podosolization of soil is an index to the forest and is promoted not only by climate but also by topographic conditions and the character of the rock. In the present paper, the habitat condition of this forest in Shikoku is briefly discussed. The Chamaecyparis obtusa forest in middle Honshu was studied by MAEDA from the phytosociological point of view. But the forest in Shikoku has hitherto not been surveyed satisfactorily. In Shikoku, the Chamaecyparis forest is found as an edaphic climax within the area from the upper part of the warm-temperate forest region to the cool-temperate forest region. This forest usually occurs on a small scale on ridges, rocky outcrops, and steep slopes of mountains, while it often occupies extensive serpentine areas in the Fagus crenata climax region. As the result of the writer's vegetational survey, Rhodoreto-Chamaecyparidetum obtusae (Chamaecyparis obtusa-Rhododendron metternichii Ass.) is described here. The floristic composition and the structure of this association are presented in Table 1. This assoclation is different from the related ones in middle Honshu by such floristic elements as Rhododendron metternichii, Rh. reticulatum, Rh. weyrichii, Tritomodon cernuus var. rubens, Hugeria japonica var. ciliaris, Ilex rugosa var, stenophylla, Il. sugeroki va. longipedunculata, Parabenzoin trilobum, Viburnum urceolatum, and others. The Chamaecyparis obtusa forest on the Pacific side of the south-western half of Japan should be included in this association.