RESPONSES OF FOREST SYSTEMS TO CLIMATIC FLUCTUATIONS IN YAKUSHIMA ISLAND,SOUTHERN JAPAN

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Forest ecosystem has been subjected to various changes of global or local environment due to natural as well as human induced eco-disturbances. Global changes including climatic fluctuations at various levels affect on function, structure, and eventually species composition of the forest ecosystem. The objective of the present co-operative research was to understand and evaluate responses of forest ecosystem against such external impacts at several different levels from leaf to shoot module, individual, population, community, and landscape, and this must facilitate mechanistic understanding of global change impacts on natural ecosystem. Yakushima Island of southern Japan was selected as study site as it represent typical, natural forest which is regulary influenced by natural disturbances such as typhoon. Typhoon No.13 of 1993, the thirs most powerful typhoon affected Japan since 1945, had strongest wind velocity ever recorded in Yakushima Island. Thus it seriously affected topography … More and vegetation especially on windward south-western side of the island. Surface erosion and land slides frequently occurred due mainly to granitic substratum which was suffered deep weathering. Although landsliding inevitably destroy the forest on it, the forest itself and its component species were relatively resistant against typhoon. Forest vegetation exhibited differentiating pattern against topographical environmental gradients such as soil water and nutrient conditions. Probably the trees are more of less adaptive against strong wind and local soil conditions. Shoot module of such trees were also studied from the viewpoint of matter production and branch autonomy, the results showed that the branch exhibited various levels of autonomy in evergreen broad-leaved tree. Leaf life span, leaf size and some other shoot phenological characteristics were compared at the three different sites of the island. Life span of evergreen leaves were 1 to 5 years and leaf life span changed in parallel with leaf size. Vegetation succession on different substratum indicated habitat preference of pioneer trees and the subsequent differentiation of successional seres. Climatic and geological constraints may act to sort different species assemblages at different sites even within a small island of Yakushima, and further development of this study project may deepen this insight. Less