Global forest restoration initiatives provide an important chance to recover biodiversity andenhance forest functions and services. Over recent decades, functional diversity (FD) has beenregarded as a key driver of the positive relationships between biodiversity and ecosystemfunctioning (BEF). Despite extensive observations on the associations between tree FD andvarious forest ecosystem functions, we still lack a sufficient mechanistic understanding of theecosystem consequences of FD in forests to provide scientific guidance for global restorationefforts. Hereafter, we revisit and seek to clarify the various pathways through which tree FDinfluences forest productivity, for example, species complementarity and dominance effects. Wediscuss 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 BEFrelationships should examine the dependence of FD effects on environmental context andpredict FD effects under environmental change scenarios. Ultimately, we propose severalstrategies for incorporating FD into forest restoration designs to reinstate BEF under current andfuture environmental conditions.