3. Results
3.1 Sampling effort
Total 545 vascular plants belonging to 106 families and 339 genera were
recorded from 96 sampling plots along the elevational gradient in the
Gyirong Valley. Out of all the vascular plants, 158 were woody (28.99%)
and 387 were herbaceous (71.01%), 337 were temperate (61.83%) and 112
were tropical (20.55%) species. For each of 300-m elevational band, the
species accumulation curves reached plateau (Fig. 2), and the
non-parametric estimated species richness were highly correlated with
the observed species richness (Choa2, R2=0.974,p <0.01; Jackknife2, R2=0.988,p <0.01; Table S2), suggesting that the sampling effort
was adequate.
3.2 Elevational trends of species range size and
environmental
variables
For all groups of vascular plants, species range size correlated
positively with elevation (β>0.7, p <0.01), and shown
uniform increasing trends along the elevational gradient as predicted by
Rapoport’s rule (Fig. 3). Woody species and tropical species were found
having relatively stronger range size-elevation relationship with higher
regression coefficient.
With increasing elevation, MAT and MAP decreased steeply whereas MATR
and TS increased monotonically, TC and PC showed a similar pattern which
generally decreased with an intermediate trough at 2400 m a.s.l., POP
and AALU showed a similar bimodal pattern with peaks at 2700 and 4200 m
a.s.l. corresponding to the Gyirong town and Zongga town, SR showed a
left-skewed hump-shaped pattern with peak at 3000 m a.s.l. (Fig. 4). MDE
of all groups of vascular plants showed a mid-peak pattern (Fig. 4, Fig.
S1).
3.3 Relationship between species range size and
environmental
variables
OLS models and SAR models showed similar results about the relationship
between species range size and environmental variables, though the
correlation would decrease when the spatial autocorrelation was taken
into account (Table 1). For all groups of vascular plants, almost all
environmental variables were significantly correlated with species range
size along the elevational gradient, except for MDE, POP, and AALU.
Among them, MAT, MAP, TC, PC, and SR showed negative relationship with
species range size, whereas MATR and TS showed positive relationship
with species range size.
3.4 Relative importance of each environmental
variables
The Random Forest models explained 58.09%, 60.24%, 51.86%, 52.05%,
and 41.93% of the variation of range size in overall species, woody
species, herbaceous species, temperate species, and tropical species,
respectively. Generally, MATR, TS, MAT and MAP are the most important
variables in explaining the elevational variation of range size across
all groups of vascular plants (Fig. 5). SR, TC, and PC also play
supplementary roles in determining the range size of vascular plants,
whereas MDE, POP, and AALU appear to be weak explanations of range size.