The global spectrum of plant form and function

Earth is home to a remarkable diversity of plant forms and life histories, yet comparatively few essential trait combinations have proved evolutionarily viable in today’s terrestrial biosphere. By analysing worldwide variation in six major traits critical to growth, survival and reproduction within the largest sample of vascular plant species ever compiled, we found that occupancy of six-dimensional trait space is strongly concentrated, indicating coordination and trade-offs. Three-quarters of trait variation is captured in a two-dimensional global spectrum of plant form and function. One major dimension within this plane reflects the size of whole plants and their parts; the other represents the leaf economics spectrum, which balances leaf construction costs against growth potential. The global plant trait spectrum provides a backdrop for elucidating constraints on evolution, for functionally qualifying species and ecosystems, and for improving models that predict future vegetation based on continuous variation in plant form and function. The authors found that the key elements of plant form and function, analysed at global scale, are largely concentrated into a two-dimensional plane indexed by the size of whole plants and organs on the one hand, and the construction costs for photosynthetic leaf area, on the other. Within the possible variety of forms that organisms can take, only a few will prove evolutionarily successful. Sandra Díaz et al. analyse a comprehensive database mapping worldwide variation in six traits critical to growth, survival and reproduction of vascular plants, and arrive at a detailed quantitative global picture of plant functional diversity. Despite enormous possible variation, the authors find that coordination among traits means that all plants can be positioned along just two axes of variation: one corresponds to overall plant form and the other is the previously characterized leaf economics spectrum. Also in this issue of Nature, Georges Kunstler et al., in a study of data from millions of trees worldwide, show that functional traits consistently predict the competitive interactions between tree species.