Maximizing functional evenness on multiple trait dimensions promotes the long-term recovery of species richness

Discovering the rules that determine how communities assembled over time are crucially needed to guide management effort aiming at restoring biodiversity in degraded ecosystems. Investigating the temporal variability of trait distributions may provide significant advances on the search for assembly rules and improve our ability to anticipate biodiversity changes. Here, we used a 17-years experiment to evaluate the effect of contrasting land-use treatments on trait and species diversity in grasslands. We found that maximizing the evenness across multiple trait dimensions simultaneously was needed to promote a high species richness, highlighting a fundamental linkage between species traits and the niche. Changes in multidimensional trait evenness preceded changes in species richness indicating that restoring assembly rules was a prerequisite to promote the long-term recovery of grassland biodiversity. The maximization of trait evenness can be used as a functional baseline to design and diagnose the effectiveness of restoration strategies on biodiversity.