Ecosystem consequences of functional diversity in forests and implications for restoration

Summary Global forest restoration initiatives provide an important chance to recover biodiversity and enhance forest functions and services. Over recent decades, functional diversity (FD) has been regarded as a key driver of the positive relationships between biodiversity and ecosystem functioning (BEF). Despite extensive observations on the associations between tree FD and various forest ecosystem functions, we still lack a sufficient mechanistic understanding of the ecosystem consequences of FD in forests to provide scientific guidance for global restoration efforts. Hereafter, we revisit and seek to clarify the various pathways through which tree FD influences forest productivity, for example, species complementarity and dominance effects. We discuss how tree FD affects ecosystem functions via changes in other trophic levels, for example, through providing more or more diverse food, habitat, or litter. Future work on forest BEF relationships should examine the dependence of FD effects on environmental context and predict FD effects under environmental change scenarios. Ultimately, we propose several strategies for incorporating FD into forest restoration designs to reinstate BEF under current and future environmental conditions.