LAUSR

Abstract From tropical to temperate forests, the effects of abiotic and biotic factors on aboveground biomass (AGB) can vary greatly, but causative relations remain poorly understood. In this study, we assessed the effects of abiotic (e.g. elevation, edaphic features) and biotic variables (e.g. species richness, functional traits, functional dispersion) on the AGB of forests across three climatic zones (tropical, subtropical, and temperate) in China. Our findings suggest that both abiotic and biotic factors had important effects on AGB variation in tropical forests, while abiotic factors played a leading role in determining AGB in temperate forests. The trait community weighted means (CWMs) explained more variation in AGB for all three forests than did functional dispersion. Only a significant effect of elevation on AGB was observed in temperate forests. The trait CWMs affected AGB in tropical and subtropical forests, but had only a weak, but significant, effect in temperate forests. Thus, the selection effect contributed to the greatest effect of biodiversity on AGB in tropical and subtropical forests. Structural equation modeling demonstrated that functional dispersion had no significant effects on AGB across different climatic zones. However, species diversity played a direct, positive role in determining AGB in tropical and temperate forests where elevational gradients existed, or indirectly through trait composition (e.g. high wood density) in subtropical forests where elevation varied slightly. Therefore, niche complementarity might also play a role in determining AGB in those forests sharing a climatic zone but varying in other characteristics.