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).