Selecting appropriate native plant species to ensure the resilience of plant communities and ecosystem services on extensive green roofs is a challenge. Plant functional strategy models provide a useful framework for identifying plant characteristics that promote plant success on green roofs, and for generalizing results obtained with limited number of species to a global flora. We analysed the dynamics of floristic composition and CSR strategies of seeded plant communities on experimental extensive green roofs under different stress conditions (substrate depths and fertilization treatments) at early establishment (4 years). Floristic composition evolved strongly over four years, with a significant reduction in species richness and equitability due to the increasing dominance of the stress-tolerant Sedum album. CSR strategies shifted from initial communities co-dominated by C and R strategies to communities largely dominated by S strategy four years later. Changes in plant communities strategy were modulated by substrate depth with higher increase in S strategy under more stressful conditions. At the installation of vegetation, the dominant factor discriminating CSR composition was fertilization supply. Substrate depth emerged as the primary factor determining CSR strategy after four years of plant community establishment. Our study supports the pattern that stress-tolerant species tend to rapidly dominate plant communities on extensive green roofs and suggests that native species selection, for implementing analogous habitat on extensive green roofs, in temperate climate, should primarily focus on natural habitats composed of stress-tolerant species. A mix of different functional strategies can be favourable to vegetation success on green roofs with environmental heterogeneity.

Abstract. Improving biodiversity in urban areas is widely recognised as part of sustainable smart cities development framework. Due to unprecedented urbanisation, there is a lack of adequate green spaces which has in turn affected the urban biodiversity. Green roofs are argued to enhance and support the biodiversity by systematic inclusion into the urban ecological network. However, its connection to the existing natural ecological areas and connectivity are not discussed at a city scale. Thus, in this study, we aim at identifying the connectivity of potential areas for developing green roofs in strengthening the biodiversity and ecological network in cities. Altogether, we observe that the potential roofs are in the near proximity of these zones. The zones with dry lawns and meadows like environment are quite limited and spatially far from each other. Thus, developing green roofs can help in connecting these spaces. In this paper, we mainly focused on bees as they play an important role in pollination and are also declining in the urban areas. Further research can incorporate more detailed analysis on foraging distances of other species. A methodology can be developed to select which zones can be targeted for specific species.