Stress tolerant species are keys to plant communities success on extensive green roof: an experimental test of CSR strategy dynamic

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.