We found 17 threatened and near-threatened plants on Minami-Iwo-To Island (the Bonin Islands) in this study, although 23 species have been recorded. Of which six species represent more than fifty percent of total number of individuals in Japan, suggesting that the island is important area for biodiversity conservation. Whole distribution range of these threatened species rarely changed, however, some populations of these species were extinct and new ones emerged during 25 years. Most species with wide distribution in 25 years ago keep approximately same range. Therefore the extinction risks of them could be low, and these species might be designated as near-threatened (NT) species. On the other hand, some species with narrow distribution in 25 years ago were not found in this study, suggesting that these species are still appropriate to be designated as threatened species. Our result showed that the assessment to extinction risk of species could be presumed by the dynamics of the distribution area in inaccessible region without anthropogenic impact.

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