Abstract
The species composition of evergreen broad-leaved forests on Hachijo-jima Island was studied. Hachijo-jima Island is one of the Izu islands, and is composed of two volcanoes of different ages : Mt. Hachijo-Fuji, a Holocene volcano, and Mt. Mihara, a Pleistocene volcano. The forest vegetation was examined by phytosociological method. The vegetation was divided into three associations (Daphniphyllo-Trochodendretum aralioides Ohba 1971, Carici-Castanopsietum sieboldii Ohba 1971 : CC and Euonymo-Pittosporetum tobira Miyawaki et al. 1971 : EP) and one community (Persea thunbergii-Prunus speciosa community: PP), and the Daphniphyllo-Trochodendretum aralioides was divided into two lower units (Irex crenata van hachijoensis lower unit : DTI and Sasamorpha borealis var. viridescens lower unit : DTS). The distributions of the DTI and PP were restricted to Mt. Hachijo-Fuji. The DTI was distributed above 430 meters a.s.l., and the PP was distributed below 550 meters a.s.l. In contrast, the distribution of the DTS was restricted to Mt. Mihara (above 490 meters a.s.l.), and the CC was distributed mostly on Mt. Mihara (below 540 meters a.s.l.). The EP was found along the seashore of both volcanoes. The distribution patterns of these forest communities was related to altitude and age of the volcanoes. Long-term succession on Hachijo-jima Island from the DTI to the DTS at higher altitude, and from the PP to the CC at lower altitude were suggested.
