Development stage-dependent effects of biodiversity on aboveground biomass of temperate forests

Abstract

Increasing evidence shows that biodiversity–ecosystem functioning relationships (BEFs) become stronger as forests develop, but much of the evidence is drawn from experiments (less than 30 years). How the biodiversity effects vary with stand development stages remains largely unexplored. Using a large temperate forest dataset with 2392 permanent plots in northeastern China, we examined the relationships between biodiversity (i.e. tree species richness, functional diversity, and functional composition) and aboveground biomass (AGB) across different development stages of temperate forests (covering all stages from young to overmature forests). Specifically, the complementarity and mass-ratio effects across different forest development stages were evaluated to elucidate emerging patterns that explain ecosystem functioning. We observed positive BEFs using both tree species richness and functional diversity, but these positive effects decreased with forest development. However, the effects of community-weighted mean (CWM) on AGB showed two peaks in young and mature stands. Interestingly, the effects of CWM on AGB became larger than the effects of functional diversity after the forests developed to near-mature/mature stands, indicating that BEFs are driven by mass-ratio effects (i.e. dominant tree species) rather than niche complementarity in old stands. The high AGB in young stands was characterized by tree species with high resource acquisition ability, however, in old stands, it was associated with tree species with both high resource acquisition ability and conservative traits. Our findings indicate how the developmental stage influences the effects of biodiversity on ecosystem functioning in natural forests. The findings tentatively advocate for a mechanistic framework of BEFs covering all developmental stages of temperate forests, which could facilitate the formulation of effective strategies for enhancing ecosystem functioning at different development stages.