Shrubs benefit from being functionally more conservative and distinct from neighbour trees

Multi‐strata forests can enhance ecosystem functioning, with interactions between overstorey trees and understorey shrubs playing a pivotal role. However, how the structure and composition of neighbouring trees, together with shrub traits, influence shrub growth remains poorly understood. In a large‐scale subtropical biodiversity experiment manipulating tree and shrub species richness, we inventoried 4411 shrubs and their surrounding trees after 11 years of interactions. We found that individual shrub biomass declined with increasing neighbour tree species richness, basal area and functional diversity, but exhibited a U‐shaped trend with the proportion of ectomycorrhizal‐associated neighbour tree individuals. Shrubs with more conservative resource‐use strategies attained higher biomass, particularly when surrounded by trees with low functional diversity and a high proportion of ectomycorrhizal associations. Biomass was also greater when shrubs were more resource‐conservative and functionally distinct from the neighbouring trees. Our findings highlight how shrub functional traits, combined with tree diversity, competition and functional traits, shape tree–shrub interactions, with shrubs benefiting more from resource‐conservative and functionally distinct traits relative to their neighbouring trees. Read the free Plain Language Summary for this article on the Journal blog.