Format: ORAL

Marta Pianta, Mariasole Calbi, Enrica Roccotiello, Lea Margraf2, Zoe Hentschel2, Wolfgang W. Weisser2

1 Department of Earth, Environment and Life Sciences, University of Genoa, Genoa, Italy 2 Technical University Munich, Terrestrial Ecology Research Group, School of Life Sciences, Freising, Germany

Green Roofs (GRs) are Nature-based Solutions that provide habitats and support biodiversity in cities. While GRs number is rapidly increasing, their ecological characterization is still poor. In particular, while all GRs are seeded or planted with plant mixtures, the development of plant communities on GRs has rarely been investigated. To unravel relationships between GRs vegetation and structural and environmental factors, this study examined 75 GRs in the city of Ingolstadt, Germany. A comprehensive sampling was carried out in the summer of 2023 within plots of 1 m2 located in the centre of each GR. GR size, height, soil depth, age and management regime were considered as predictor variables. The plant taxonomic diversity of the roof communities was calculated using Hill numbers. The main drivers of species composition were identified through a Non-Metric Multidimensional Scaling (NMDS) and selected variables were used to fit a Redundancy Analysis (RDA). GLMs were then fitted to model diversity indices and bryophyte coverage across GRs in relation to selected factors. Differences in bryophyte coverage according to management type were also assessed with a Kruskal-Wallis test. The NMDS showed that the most influential variables on GRs plant communities are age, soil depth, mowing and weeding practices (9% of the variance explained in the RDA). Plant diversity tends to increase with increasing soil depth and GR height. Bryophyte cover decreases with increasing soil depth. In addition, bryophyte cover is significantly different between unmanaged and regularly mown or weeded GRs. Our study shows that plant communities of GRs are affected by several roof variables, and that soil depth, roof height and management strongly affect plant communities developing on the roofs. The results may provide useful insights for more environmentally and financially sustainable design and management of GRs.