| Research Abstract |
Forest structure and tree traits were studied in several subtropical/warm-temperate broad-leaved forests in southern Japan including Okinawa and Yakushima Islands, Mt. Kiyosumi, Chiba, and Mt. Dokura, Miyagi. Evergreen broad-leaved trees of tropical origin constitutes the northern limit of the latitudinal distribution in southern to central Japan. There are two groups of trees having characteristic features such as bud type (naked, hypsophyllary and scaled buds), leaf size sensu Raunkiaer, branching architecture, and niche within and between forests in the northern limit of evergreen broad-leaved forests. The canopy trees have mostly scaled-bud, notophyll, proleptic branching, and high C/N ratio of their leaves while understorey trees have hypsophyllary-bud, microphyll, sylleptic branching, and low C/N ratio. In the undersorey layer of the forest, pole stage trees of canopy species allocate more to shoot extension rather than to expand foliage surfaces in a shoot-module level while und
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erstory species allocate more to foliage expansion and thus tolerate deep shade in the undestorey layer. Branching type of trees can be categorized into two, i.e. sylleptic and proleptic. Most of the canopy species have proleptic branching with a more or less homogeneous branches in their performances (length, number of leaves). Understorey species, on the other hand, have sylleptic branching with stronger performances of the main shoot than sylleptic lateral branches. Prolepsis is more common in the northern species while syllepsis is more common in southern species in the Japanese Cinnamomum species investigated. Syllepsis is more tropical in nature in their growth habit and the trees with sylleptic branchings are found in the southern most Cinnamomum doederleinii and Cinnamomum daphnoides partly. Cinnamomum japonicum with the widest and the northern most distribution in Japan has solely proleptic branchings. The trees having leaves with high C/N ratio are more concentrate to canopy and ridge habitats while those with low C/N ratio are to understorey and valley habitat though the trend is rather weak because of the wide ranging species. It is suggested that the habitat segregation is strongly correlated with the nutrient turnover in the habitat and tree growth habit. Less
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