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A new study published in shows that tree diversity consistently promotes productivity through fostering greater canopy structural complexity (CSC). Species complementarity is the main driver, with its positive effects strengthening over time.

Led by Prof. Liu Xiaojuan from the Institute of Botany of the Chinese Academy of Sciences, the researchers integrated four-year, UAV-borne LiDAR assessments of tree crowns and ground-based growth measurements of 38,088 trees growing in 482 plots containing one, two, four, eight, 16, or 24 tree species. These measurements were taken within a large forest biodiversity experiment in southeast China (BEF-China) 11 to 15 years after planting.

The researchers found that increased CSC largely explained the positive biodiversity–productivity relationships. They also found that "overyielding"—the production of more biomass by mixed-species tree plots—was driven by the positive effect of species complementarity on CSC, an effect that strengthened with tree age.

This suggests that in mixed stands, different species can better fill the aboveground canopy space with their non-overlapping tree crowns, while in less diverse or even monocultures the canopy space is not occupied so evenly and thus light is used less efficiently.

"Our study suggests that forest managers should consider increasing CSC by selective harvesting and replanting diverse species to sustain high productivity over longer time spans," said Prof. Liu, corresponding author of the study.

Prof. Bernhard Schmid, a core author of the study, added, "These findings are the first to demonstrate such complementary use of aboveground space in a tree biodiversity experiment."

This study demonstrates 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.

Looking ahead, the researchers plan to investigate CSC effects at later successional stages of forest development and across different forest types. They also hope to develop methods of manipulating CSC independent of tree species richness and other covariates such as functional diversity to test their conclusions.