Plant species richness and vegetation types along a warm-temperate to subalpine gradient in the Omine Mountains, western Japan

To explore the variation in species richness of vascular plants along environmental gradients and among vegetation types from evergreen broad-leaved to coniferous forests in the Omine Mountains, western Japan, the numbers of living vascular plant species were recorded in 300 plots (4 m × 10 m) along the gradients of elevation, topography, slope inclination, and the number of vegetation layers. A total of 246 species belonging to 91 families were found at elevations of 634–1,915 m. With an increase in the elevation, the number of fern species showed no change, while the number of herb, tree, and all plant species showed hump-shaped responses, peaking at approximately 1,750 m, 1,000 m, and 1,100 m, respectively. The topographic position index for ferns was more important determinants than elevation. The elevation and the number of vegetation layers for herbs and the elevation for trees were important factors. The slope inclination for herbs and trees were slightly influencing factor. Cluster analysis revealed that five plant community groups, characterised by elevation, showed great variation in plant species richness and composition among groups. Some groups were located in the same altitudinal zones with no obvious differences in topography. Since the global warming causes the upward shift of the plant communities, the mountaintop population of Abies veitchii and narrow-ranged species are suggested to become extinct locally, and the herb community with high species richness at high elevations is suggested to disappear or change in the Omine Mountains.