The ability to explain why multispecies assemblages produce greater biomass compared to monocultures has been a central question in community ecology. Species contributions to function are the outcome of two processes: niche complementarity and a selection effect that is influenced by fitness (and thus competitive) differences, and both can be approximated with measures of species’ traits. Here I examine the influence of functional diversity on function using a diversity-ecosystem function experiment using 13 traits. Trait relationships with above ground productivity were assess using two functional measures: one that assesses trait dissimilarity (functional dispersion) and community weighted mean trait.
I show that the selection effect was strongest in communities with low trait dissimilarity, while complementarity was greatest with high trait dissimilarity. Further, the selection effect was best explained by a single trait, average plant height. However, complementarity was correlated with dissimilarity in a number of different traits, representing both above and below ground processes. By identifying the relevant traits that explain components of species’ contributions to ecosystem function, we obtain the ability to predict which combinations of species will maximize ecosystem function.