Combinations of plant species with complementary traits have the potential to maximize ecosystem services on green roofs

Ecosystem services are critical in urban areas, where the majority of humanity now lives. In many cities, extensive green roofs are planted with succulent nonnative Sedum species that provide rapid vegetative cover, retain stormwater, insulate buildings, and provide cooling through evapotranspiration. If diverse native plant species were used on green roofs in addition to Sedum , green roofs could also support greater biodiversity. Ecosystem services provided by Sedum are documented within temperate climates but the contributions of native forbs are relatively unknown, largely due to difficulties in plant establishment. Survival, drought-tolerance, and stormwater capture of native plants may be enhanced by inoculating the soil with indigenous arbuscular mycorrhizal (AM) fungi. In this experiment, we tested the hypotheses that green roofs planted with diverse native species would provide the ecosystem services of thermal building insulation, evapotranspiration, and stormwater capture and be aided by inoculation with indigenous AM fungi. We used green roof trays in a multi-factorial design to test for the effects of vegetation community and AMF inoculation on provisioning of ecosystem services in two locations. Despite slower establishment, native plant communities showed greater stormwater capture and evapotranspiration rates compared to Sedum communities. However, Sedum provided greater thermal insulation during the hot months of summer. Inoculation with AM fungi did not improve plant establishment or provisioning of ecosystem services. Overall, our results suggest that planting a variety of native prairie grasses and forbs may maximize ecosystem services provided by urban green roofs.