Tree diversity promotes crown complementarity and canopy packing through variation in architecture traits

Abstract Crown complementarity and canopy packing are key drivers of tree diversity effects on ecosystem productivity. Tree architecture is an important determinant of height extension, light capture and crown development in trees, but how architectural traits mediate the effects of tree diversity on crown complementarity and canopy packing remains unclear. Here, we examined how the effects of tree diversity on crown complementarity and canopy packing are directly and indirectly mediated by variation in architectural traits in a tree diversity experiment on Putuo Island in eastern China. The results showed that tree species richness and functional diversity increased variation in crown expansion traits, including twig intensity (number of twigs per first-order branch), branch intensity (number of branches per individual) and crown volume. In addition, tree diversity had divergent effects on leaf arrangement traits, with greater variation in leaf intensity (number of leaves per twig) and petiole diameter, but reduced variation in twig angle and petiole length among interacting individuals. Greater variations in crown volume, branch intensity, leaf intensity and twig intensity therefore promoted both crown complementarity and canopy packing. Our findings suggest that variations in crown architectural traits play crucial roles in mediating the positive effects of tree diversity on tree crown complementarity and canopy packing. Our study highlights that diversity-driven variation in crown architectural traits provides a key mechanistic pathway linking tree diversity to canopy processes in early-stage experimental forests, with important implications for ecosystem structure and productivity.