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

在日本亚热带海洋岛屿千岛岛的演替早期，研究了外来灌木银合欢入侵对当地演替中期树种木荷建立的直接和间接影响。本研究比较了优势种和金边沙打旺对两地沙打旺种子萌发和移栽幼苗生长的影响。白头落叶松优势立地的生长速度低于东方落叶松优势立地。白头落叶松优势种的种子发芽率和幼苗生长速率均低于东方落叶松优势种。这些结果表明，白头斑潜蝇直接入侵群落，通过抑制黑头斑潜蝇种子萌发和幼苗生长，从而阻止了斑潜蝇的建立，从而改变了群落的演替途径。根据等位酶分析，稻瘟病菌有两个遗传隔离群，但分布格局和株数不受遗传多样性水平的影响。在所有的分类群中，海洋特有种的遗传多样性都很高，并且大多数多样性存在于种群内。与海洋地方病的一般概念相反，高遗传多样性和低种群分化是一个独特的特征组合。

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.