Direct and indirect effects of environmental factors, spatial constraints, and functional traits on shaping the plant diversity of montane forests

Understanding the relative importance of the factors driving the patterns
of biodiversity 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 addition, most existing studies
make no distinction between direct and indirect effects of environmental
factors, 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 = 0.10, P value = 0.001), shrubs (r = 0.19, P value =
0.001), or overall plant diversity (r = 0.18, P value = 0.001) in montane
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.