Abstract:

Aims: Understanding how biodiversity regulates forest carbon sequestration is essential for accurately assessing forest carbon sink potential and enhancing forest carbon storage in the context of carbon peaking and carbon neutrality goals. However, the relative contributions of species composition, species diversity, and stand structure to forest carbon storage remain poorly understood in cold-temperate mixed forests. 

Methods: Using permanent plots established in the southern Greater Khingan Mountains of Northeast China, we quantified aboveground carbon storage (AGCS) as an indicator of forest carbon sink function. Species richness was used to represent biodiversity and test the niche complementarity hypothesis, whereas species composition was quantified using principal coordinates analysis to evaluate the biomass ratio hypothesis. Stand age, stand density, coefficient of variation of DBH, soil nutrients, and elevation were also incorporated into the analyses. Generalized least squares (GLS) models and piecewise structural equation modeling (pSEM) were applied to identify the key drivers and underlying pathways regulating AGCS. 

Results: (1) Species composition and stand density were the dominant biotic drivers of AGCS, with species composition exhibiting the strongest positive effect, partially supporting the biomass ratio hypothesis by highlighting the significant contribution of dominant species. (2) Species richness also had a positive effect on AGCS, but its contribution was substantially weaker than that of species composition, indicating a relatively limited role of niche complementarity in cold-temperate forests. (3) Stand age had no direct effect on AGCS but indirectly influenced AGCS by regulating stand density and species dominance. 

Conclusions: These findings reveal the mechanisms underlying forest AGCS from the perspectives of species composition, biodiversity, and stand structure, providing a theoretical basis for evaluating carbon sink potential and developing sustainable forest management strategies in cold-temperate forests.

Key words: biodiversity, species composition, structural diversity, aboveground carbon storage, conifer-broadleaf mixed forests