APPEARANCE CHARACTERISTICS IN VEGETATION UNITS OF STEWARTIA MONADELPHA AND S. SERRATA IN MONTANE SUMMER-GREEN BROAD-LEAVED FORESTS IN THE AMAGI MOUNTAINS

Abstract

Stewartia monadelpha and S. serrata are distributed in the Amagi Mountains of the Izu Peninsula, Shizuoka Prefecture. These two species are morphologically similar and have overlapping distributions. However, it is not clear how they divide forest habitats within the same mountain. In the seedling stage, both species appear not only in the forest understory but also in the pioneer stands of herb and shrub communities. Focusing on the layers above shrubs, S. serrata shows high coverage and sociability in the community types of Weigelo-Alnetalia firmae Ohba et Sugawara 1979 and Fraxino-Ulmetalia Suz.-Tok. 1967, which indicates unstable site conditions regardless of ecological factors such as geomorphism and dry–wet gradients. Compared with S. serrata, S. monadelpha is more ubiquitous. In particular it occurs in all layers of beech forest, Saso-Fagetalia crenatae Suz.-Tok. 1966, and has a similar regeneration process to beech. The above information is insufficient to explain the habitat isolation of S. monadelpha and S. serrata using ecological factors such as geomorphism and dry–wet gradients; however, we predict that this is determined by dynamic factors such as life type and disturbance regime.