Significant effects of biodiversity on forest biomass during the succession of subtropical forest in south China

Subtropical forests across south China have been extensively affected by anthropogenic disturbances with potential profound effects on plant biodiversity and ecosystem function (BEF). However, whether and to what degree biodiversity influences biomass of subtropical forests remains uncertain. In this study, we analyzed the effects of tree biodiversity (species diversity, functional diversity and phylogenetic diversity) on stand biomass at three stages (early, mid and late) of succession in subtropical forests. As forest succession progressed, we found that the changes in species diversity were different compared with those of functional and phylogenetic diversity. Most of the indices of species and functional and phylogenetic diversity were not significantly correlated with stand biomass at two spatial grains (plot sizes of 10 m × 10 m and 20 m × 30 m). However, when other abiotic and biotic factors (i.e., altitude, canopy light, stem density and forest phase) were included with diversity indices in mixed models to explain biomass, the effect of functional diversity on biomass was significant at both resolution. For species diversity indices, the effect was significant at the 20 m × 30 m resolution, and phylogenetic diversity had no significant effect. Our results indicate that biodiversity affects forest biomass during the succession of a subtropical forest and suggest that functional diversity may provide a better metric than species or phylogenetic diversity for determining the biodiversity effect on biomass. Moreover, our results indicate that the diverse conclusions reached in other BEF analyses might be explained by differences in the plot size examined and the diversity metrics selected. Because the bivariate relationship between biodiversity and biomass can be strongly confounded by covarying abiotic and biotic factors, we suggest that the effects of abiotic factors, succession stage, and management practices on BEF should be carefully considered in future research.