Abstract
We have studied the structure and altitudinal zonation of the warm temperate forests on the volcanic Mikura-jima Island, one of the Izu Islands, Japan. The forest can be divided into three main zones : a low-altitude Castanopsis forest zone, a middle-altitude transitional Castanopsis forest zone and a higher-altitude Buxus-Eurya-Trochodendron mixed forest zone. The forest has several distinctive features. Firstly, the species composition of the mixed forest differs from the evergreen broad-leaved forests found at a similar altitude on the Japanese mainlands. Secondly, tree species diversity increases with altitude. Thirdly, tree height decreases with increasing altitude, and forthly, leaf size decreases from notophyllous at lower altitudes, to microphyllous and nanophyllous at higher altitudes. The decline in tree height and the change in leaf size may be characteristic of small volcanic islands in the warm-temperate region of Japan.
