Canopy structural diversity mediates the impact of anthropogenic disturbance on forest biomass

Abstract The three-dimensional configuration of tree crowns controls resource distribution within canopies, thus driving forest ecosystem functioning, but landscape fragmentation and canopy structure degradation is causing forest biomass loss. Yet, how canopy structural diversity mediates the impact of anthropogenic disturbance on forest biomass remains poorly understood in urbanized regions, where population aggregates in cities and many of the rural areas were converted into built-up land. Here, we combined the Global Ecosystem Dynamics Investigation (GEDI) spaceborne LiDAR with Sentinel imagery to map forest aboveground biomass density (AGBD) at 30 m resolution across Beijing, China. We further assessed the relative contributions of canopy structural diversity (plant area index, PAI and canopy height diversity, H), anthropogenic disturbance (land surface temperature, LST and road network density, RND), and environmental factors (elevation and soil organic matter content, SOM) to AGBD using Bayesian regression modeling, and clarified the direct and indirect pathways linking them to AGBD by structural equation modeling. Results showed that (1) high biomass values were concentrated in mountainous forests, while fragmented lowland forests near urban infrastructure had substantially lower biomass; (2) human disturbance predominantly explained forest biomass variations (66%), followed by structural diversity (20%) and environmental factors (14%), while canopy structural diversity promoted biomass mostly through PAI; and (3) human disturbance (RND and LST) negatively affected biomass, both directly and indirectly by reducing PAI. Our findings highlight canopy structural diversity as a critical mediator between urban disturbance and forest biomass, and demonstrate the potential of GEDI-based monitoring to inform vegetation restoration and sustainable regional planning.