Biogeographic study on plant distribution in forest islands.

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The flora and vegetation of twenty-five forested tracts, or forest islands, isolated in rural or urban areas were studied in western Kyushu, Japan. The project was designed to clarify the species-area relations and the critical size of forest islands for preserving rare plant species. The total number of listed plants was 188 species. The smallest number in a tract was 29 in a 0.2 ha tract and the largest was 114 in a 23 ha tract. The species number was positively correlated with the tract size (r=0.895).The plant species listed can be categorized into 5 groups according to their behavior in the naturalness and the coastal-to-inland gradients. Species group I was assigned to those found in seral or disturbed forests and V was to natural or primeval forests. The species group V was further classified into 3 subgroups of 0 (species distributed widely but only in natural forests), 1 (species restricted to inalnd) and 2 (species restricted to coastal lowland). The species number of group V (all together of subgroups 0, 1 and 2) was not correlated with the tract size, but strongly affected by human disturbances and impact.Bryophytes in the forest islands studied were classified into 3 groups according to their substrata as epiphytic, epilithic and terrestrial. In each of the 3 groups, species restricted to natural areas were found. Examples are Chrysoclaldium retrorusum, Barbella asperifolia, and Neacroporium flagelliferum in the epiphytic group, Ctenidium capillifolium, Eurhynchium polystictum, and Thuidium bipinnatulum in the epilithic group, and Calypogeia tosana, and Rhizogonium dozyanum in the terretrial group.