Tree Community Overyielding During Early Stand Development is Explained by Asymmetric Species-Specific Responses to Diversity

1. Recent long-term tree biodiversity experiments have shown that diversity effects on productivity tend to strengthen over time, as complementarity among constituent species increases over the course of forest development. However, these community-level metrics only account for the net outcome of multiple interactions among species and, thus, do not inform about the individual species' responses to diversity. 2. In this study, using 11 years of growth records from a large diversity experiment, we explored how species respond to diversity based on their functional traits and those of their heterospecific neighbours over time and analysed their contribution to the community-level overyielding. 3. We show species-specific responses to diversity, with fast-growing deciduous species rapidly performing better in mixtures relative to monocultures, than slow-growing evergreen species. Moreover, we find that species productivity in mixtures enhances over time as the proportion of slow-growing evergreen species in the heterospecific neighbourhood increases. These patterns of response of species scale up and explain community overyielding, which occurs primarily in deciduous-evergreen mixtures and is explained by the overyielding of deciduous species overcompensating the poor performance of evergreen species. 4. This study sheds light on the temporal dynamics of species responses to diversity, which together help improve our understanding of community-level overyielding over the course of stand development.