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

森林生态系统由于自然和人为的生态干扰而受到全球或局部环境的各种变化。全球变化，包括不同层次的气候波动，影响着森林生态系统的功能、结构，并最终影响着物种组成。本次合作研究的目的是了解和评价森林生态系统对这些外部影响的响应，从叶到茎、模块、个体、种群、群落和景观等多个不同的层面，这将有助于理解全球变化对自然生态系统的影响。选择日本南部的屋久岛作为研究地点，因为它是典型的天然森林，经常受到台风等自然干扰的影响。1993年第13号台风是1945年以来影响日本的第三强台风，其在屋久岛的风速是有记录以来最高的。因此，它严重影响了地形和植被，特别是在岛的西南迎风面。花岗岩基底受深度风化作用，地表侵蚀和滑坡现象频繁发生。虽然山体滑坡不可避免地破坏了其上的森林，但森林本身及其组成物种对台风的抵抗力相对较强。森林植被随土壤水分和养分等地形环境梯度呈现分异格局。也许这些树更能适应强风和当地的土壤条件。从物质生产和枝自主性的角度研究了常绿阔叶树的枝模块，结果表明，常绿阔叶树枝具有不同程度的枝自主性。比较了岛上3个不同地点的叶片寿命、叶片大小和其他一些物候特征。常绿叶片的寿命为1 ~ 5年，叶片寿命随叶片大小的变化而变化。不同基质上的植被演替表明了先锋树的生境偏好和演替序列的分化。即使在屋久岛的一个小岛上，气候和地质条件的限制也可能对不同地点的不同物种组合进行分类，本研究项目的进一步发展可能会加深这一认识。少

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