Studies on vegetation recovery in an island ecosystem in the Bonin Islands

本文研究了外来灌丛Leucaena leucocephala入侵对日本副热带海岛父岛（Chichijima）早期中游演替原生木本木本（Schima mertensiana）随后建立的直接和间接影响。比较了优势种和牙买加金丝桃对两地梅氏金丝桃移栽苗种子萌发和生长的影响。在白头蠓优势区，牙买加蠓的生长低于东方蠓优势区。白大头草优势区墨氏天牛种子发芽率和幼苗生长率均低于东方天牛优势区。这些结果表明，白大头刺直接在白大头刺入侵群落中抑制白大头刺种子萌发和幼苗生长，从而阻止了白大头刺的建立，这可能改变了白大头刺群落的演替途径。对博宁群岛特有属博宁属（Boninia） 16个居群和特有种西村桉（Euodia nishimurae）的遗传变异数量和分布进行了分析。等位酶分析结果表明，稻瘟病菌的遗传多样性水平不受分布模式和株数的影响，但存在两个遗传分离群。在所有分类群中，海洋特有物种均具有较高的遗传多样性，且大部分遗传多样性存在于种群内。高遗传多样性和低种群分化是一种与一般海洋特有物种概念相反的独特性状组合。

We investigated direct and indirect effects of an invasion of alien shrub, Leucaena leucocephala, on subsequent establishment of native mid-successional tree, Schima mertensiana at early-successional stages in Chichijima Island, a subtropical oceanic island in Japan. We compared effects of dominant species and S.jamaicensis on seed germination and growth of transplanted seedlings of S.mertensiana between the two sites. Growth of S.jamaicensis established at the L.leucocephala dominated site was lower than those at T.orientalis dominated site. Seed germination rate and seedling growth rate of S.mertensiana at the L.leucocephala dominated site were lower than those at the T.orientalis dominated site. These results suggest that there was a prevention of establishment of S.mertensiana caused by an inhibition of seed germination and seedling growth of S.mertensiana by L.leucocephala directly at L.leucocephala invaded communities, which potentially changed a successional pathway in the communities.The amount and distribution of genetic variations were examined in 16 populations of endemic genus Boninia and an endemic species Euodia nishimurae in Bonin Islands. Based on allozyme analysis, two genetic isolated groups were recognized in B. grisea var.grisea, while distributional patterns or numbers of trees were not affected to levels of genetic diversities. For all taxa, high genetic diversities for oceanic endemics were detected, and most of diversities were possessed within populations. High genetic diversity and low population differentiation is a unique character combination contrary to general concepts of oceanic endemics.