Functional diversity as a framework for novel ecosystem design: The example of extensive green roofs

Novel urban ecosystems have recently gained importance and a consensus grows that ecosystem services are linked to ecosystem properties that in turn can be predicted by functional diversity (FD) of plant communities. Ensuring quality of life in cities is essential and approaches to improve ecosystem services should be encouraged. Here we analyzed the initial plant composition of commercial extensive green roof systems in terms of FD and propose two methods to compose species lists that maximize FD. Clustering techniques grouped the systems in three green roof types that differ in species richness and composition, substrate depth and installation method. Differences in FD and species richness between the types were considerable and correlations between FD and species richness were strongly positive, suggesting that species-rich systems generally have higher FD and thus offer better ecosystem services. Green roof systems that comprise only succulents have significant lower FD values compared to systems containing more diverse vegetation. Within the green roof types there was room for improvement of FD. Based on a species trait dissimilarity matrix, species lists that maximize FD for every green roof type were created. FD analysis of novel ecosystems enables the design of both species-poor and species-rich green roof systems with improved overall ecosystem services value. The described approach is generic in nature and can be used for a broad range of novel ecosystems and urban green elements. We believe that designing functional diverse plant systems will support a more sustainable urban planning and improve the quality of urban life.