The aim of this study was to evaluate the comparative importance of habitat types for the conservation of biodiversity. We determined the number of endangered vascular plant species for each habitat type using the regional Red Data Book that contains information for five prefectures in the Chugoku region, western Japan, together with data on the area covered by each habitat type obtained from the fifth national vegetation survey. The habitat types were classified as "forest", "agricultural field," "wetland," "rocky ground," "grassland," or "seaside." Although many of the listed endangered species belonged to forest habitats, at the regional level, the species/area ratios were higher in the grassland, wetland, and seaside habitats than in the forest and agricultural field habitats. However, the conservation priorities for the endangered plant species in relation to habitat type showed only a slight variation among the prefectures examined.
