Species richness of seed plants and ferns along a temperate elevational gradient in central Japan

Abstract

We evaluated richness patterns of all vascular plants in central Japan with respect to spatial and climatic factors. This evaluation was performed by analysing a database that contained information on 150,806 herbarium specimens from this region. We analysed the area-corrected and rarefied species richness of all vascular plants, seed plants and ferns at 100-m elevational bands. The area-corrected species richness showed an asymmetric hump-shaped pattern for total and seed plants with a plateau in a higher elevation, whereas fern species richness showed a decreasing pattern. The rarefied species richness showed a low-plateau pattern in all cases because of the low threshold; however, species richness by rarefaction of specimens down to a higher threshold supported the area-corrected pattern. Thus, we concluded that total and seed plant richness showed a hump-shaped pattern, and that fern richness showed a decreasing pattern. Area, temperature and precipitation were significantly correlated with species richness, and climatic factors explained more variation in species richness of ferns compared with that of seed plants. When the species were divided based on range size, climatic factors explained more variation in small-ranged species richness than spatial factors, whereas spatial factors did so in large-ranged species richness. In addition, small-ranged species richness of seed plants showed a bimodal pattern with peaks at low elevation and high elevation probably because the mountains in central Japan play a role as refugia for Japanese alpine plants during climatic oscillations, or an artefact.