Diverse forests make complementary use of canopy space and produce more biomass

Numerous studies have documented positive biodiversity–productivity relationships in both observational and experimental forest biodiversity studies. The horizontal distribution and vertical stratification of tree crowns can affect light interception and tree growth, thus driving forest productivity and carbon storage. However, the role of canopy structural complexity (CSC) in modulating biodiversity–productivity relationships and their change over time have rarely been quantified.

In this talk, I will present my project using 4-year consecutive UAV-borne LiDAR and ground-based growth field measurements of 38,088 trees growing in 482 plots containing 1, 2, 4, 8, 16, or 24 tree species, 11 to 15 years after planting, within a large-scale forest biodiversity experiment in southeast China (BEF-China). We found significant positive effects of tree species richness on multidimensional CSC indices (i.e., canopy cover, foliage height diversity, and box dimension)—encompassing horizontal, vertical, and holistic 3D canopy structures—across a broad diversity gradient over the 4 years. And community aboveground biomass significantly increased with all CSC indices. Additionally, the positive effect of tree species richness on community aboveground biomass was mediated by multifaceted CSC in all years studied, from 2021 to 2024. Furthermore, our results revealed significant positive relationships between the three CSC indices and net biodiversity effects or complementarity effects across the 4 years, but not with selection effects. And the positive relationships between the three CSC indices and complementarity effects strengthened from year to year.

In summary, our study experimentally demonstrates how tree species richness increases CSC and how CSC relates to increased community aboveground biomass and biodiversity complementarity effects. These findings reveal the key role of complementary use of aboveground space in a tree biodiversity experiment. Our study emphasizes the need to consider CSC and its role in mediating biodiversity complementarity effects to promote biomass production, carbon storage, and thus contribute to climate change mitigation in long-term afforestation projects.