3.2 Alpha diversity
The alpha diversities of the plant groups exhibited different responses to elevational distribution (Figure 1). All the coefficients, except that for ferns, in the GLMs were significant. Both the total and tree alpha diversities linearly decreased with elevation (Figure 1a, 1b), whereas that of herbs increased (Figure 1d). The alpha diversities of shrubs and bryophytes were fitted by second-order polynomial and that of shrubs showed a positive quadratic curve with the highest value at an elevation of 2800 m (Figure 1c), whereas that of the bryophytes showed a negative quadratic curve displaying a hump-shaped pattern with higher values at ~2000 m (Figure 1f). Notably, the alpha diversity of herbs increased with elevation overall; however, a lower value was recorded at one 2800 m-plot where the stone pine trees dominated.
The results for alpha diversity and climatic factors obtained using GLMs are shown in Table 1. The variable Tempann and Tempsnow had significant positive effects on the alpha diversities of trees and ferns. The alpha diversity of shrubs was negatively correlated with RHgrow, whereas that of herbs was positively correlated with the snow cover and that of bryophytes was positively correlated with RHgrow.
3.3 Beta diversity
When beta diversity (based on the Bsin index) was plotted against elevation (Figure 2, Table S2), the βsinindices of shrubs and ferns were not calculated in several plots because of the zero denominator in the fraction of βsin (Figure 2c, 2e). Although βsin for the total number of species gradually increased with elevation (Figure 2a), those for shrubs and herbs strongly increased above the subalpine-alpine transition zone (Figure 2c, 2d).