Elevation is involved in determining plant diversity in montane ecosystems. This study examined whether the species distribution of plants in the Yatsugatake Mountains, central Japan, substantiated hypotheses associated with an elevational diversity gradient. Species richness of trees, shrubs, herbs, ferns, and bryophytes was investigated in study plots established at 200-m elevational intervals from 1800 to 2800 m. The changes in plant diversity (alpha and beta diversities, plant functional types, and elevational ranges) with elevation were analyzed in relation to climatic factors and elevational diversity gradient hypotheses, that is, mass effect, mid-domain effect, and Rapoport’s elevational rule. A comparison of alpha and beta diversities revealed that different plant groups respond variably to elevation; the alpha diversity of trees and ferns decreased, that of herbs increased, whereas the alpha diversity of shrubs and bryophytes showed a U-shaped relationship and a hump-shaped pattern. The beta diversity of shrubs, herbs, and bryophytes increased above the subalpine–alpine transition ecotone. In accordance with these changes, the dominance of evergreen shrubs and graminoids increased above this ecotone, whereas that of evergreen trees and liverworts decreased. None of the plant groups showed a wide elevational range at higher elevations. These elevational patterns of plant groups were explained by climatic factors, and not by elevational diversity gradient hypotheses. These patterns were further influenced by plant–plant interactions via competition for light availability and physical habitat alternation.
Aim: This study examined whether the hypotheses associated with species distribution could substantiate the elevational patterns of plants. Location: Mount Yatsugatake in central Japan. Taxon: Embryophyte Methods: The species richness of plant groups (trees, shrubs, herbs, ferns, and bryophytes) was investigated within study plots established at 200-m elevational intervals from 1800 m to 2800 m. The changes in species richness (alpha diversity) with elevation were analysed in relation to climatic factors and the hypotheses pertaining to the elevational distribution of plants, i.e., mass effect, mid-domain effect, and Rapoport’s elevational rule. The elevational patterns of beta diversity, plant functional types, and elevational ranges of plant groups were examined. Results: The comparison of alpha and beta diversity revealed that the different plant groups variably responded to elevation; the alpha diversity of trees and ferns decreased, that of herbs increased, whereas that of shrubs and bryophytes showed a positive and negative quadratic curve, respectively. The beta diversity of shrubs, herbs, and moss abruptly increased above the subalpine-alpine transition zone. In accordance with these changes, the dominance of evergreen shrubs and graminoids increased, whereas that of liverworts decreased at the elevation zone. Regarding the elevational ranges, no plant group showed a wider elevational range at higher elevations. Main conclusions: The elevational patterns of the plant groups were determined by the climatic factors and their effects on plant-plant interactions. Notably, these interactions were presented based on the changes in plant functional types, supporting the elevational patterns of plant diversity. Our finding indicates the importance of studies on elevational patterns using multi-plant groups and multiple indices of plant diversity.