Size matters for linking traits to ecosystem multifunctionality

A priority research field addresses how to optimize diverse ecosystem services to people, including biodiversity support, regulatory, utilitarian and cultural services. This field may benefit from linking ecosystem services to the sizes of different body parts of organisms, with functional traits as the go-between. Using woody ecosystems to explore such linkages, we hypothesize that across stem diameter classes from trunk via branches to twigs, key wood and bark functional traits (especially those defining size-shape and resource economics spectra) vary both within individual trees and shrubs and across woody species, thereby together boosting ecosystem multifunctionality. While we focus on woody plants aboveground, we discuss promising extensions to belowground organs of trees and shrubs and analogs with other organisms, for example, vertebrate animals. Incorporating contributions of different sizes within and between organismal organs to trait variance could improve our understanding of how biodiversity supports ecosystem multifunctionality.The size-centered hypothesis shows how, for trees and shrubs, the combination of trait variation vertically (between organs) and horizontally (among individuals and species) could underpin ecosystem multifunctionality.A key aspect of size–trait relations is the variance across woody organs in traits belonging to the size and shape spectrum and the resource economic spectrum.Ecosystem ecology would benefit from more attention to size variance of organisms.