Understanding the relative importance of the factors driving the patterns of biodi-
versity is a key research topic in community ecology and biogeography. However, the 
main drivers of plant species diversity in montane forests are still not clear. In addi-
tion, most existing studies make no distinction between direct and indirect effects of 
environmental factors and spatial constraints on plant biodiversity. Using data from 
107 montane forest plots in Sichuan Giant Panda habitat, China, we quantified the 
direct and indirect effects of abiotic environmental factors, spatial constraints, and 
plant functional traits on plant community diversity. Our results showed significant 
correlations between abiotic environmental factors and trees (r = .10, p value = .001), 
shrubs (r = .19, p value = .001), or overall plant diversity (r = .18, p value = .001) in mon-
tane forests. Spatial constraints also showed significant correlations with trees and 
shrubs. However, no significant correlations were found between functional traits 
and plant community diversity. Moreover, the diversity (richness and abundance) of 
shrubs, trees, and plant communities was directly affected by precipitation, latitude, 
and altitude. Mean annual temperature (MAT) had no direct effect on the richness of 
tree and plant communities. Further, MAT and precipitation indirectly affected plant 
communities  via  the  tree  canopy.  The  results  revealed  a  stronger  direct  effect  on 
montane plant diversity than indirect effect, suggesting that single-species models 
may be adequate for forecasting the impacts of climate factors in these communities. 
The shifting of tree canopy coverage might be a potential indicator for trends of plant 
diversity under climate change.

In 2017, 107 random sampling plots in montane forests were collected 
from north to south, spanning the entire Sichuan Giant Panda habi-
tat. The sampling strategy and field site information are shown in Li et 
al. (2019). The elevation within the sampling plots varied significantly 
(from ca. 2,000 to 3,600 m a.s.l.) (Li et al., 2019). The main vegetation 
types in those plots were coniferous and broad-leaved mixed forests, 
and evergreen and deciduous broad-leaved mixed forests. Using ques-
tionnaires, we surveyed 72 local people from Minshan, Xiaoxiangling, 
and Qionglai in the Sichuan Giant Panda habitat in 2017. Those local 
villagers mainly participated in the local Giant Panda habitat conser-
vation.  The  survey  information  included  if  there  was  any  interfer-
ence in the sampling plots. In addition, we observed the plant species 
composition and environment in the montane forests to choose only 
mature forests. We finally screened 107 mature forest sampling plots 
without human interventions. Vegetation surveys were conducted be-
tween July and September 2017 (the peak period of plant growth). All 
plots were located at least 150 m from the road to avoid edge effects. 
Within each plot, trees in a 20 m × 30 m subplot and shrubs from three 
5 m × 5 m subplots were studied. Data from the three subplots within 
each plot were then pooled. The plant species, number of individu-
als (abundance), and coverage of each layer (e.g., tree, shrub) were re-
corded (Table S1).