Cities are defined as heterotrophic systems (Odum, 1983) as they depend mainly on external resources and cause habitat loss and fragmentation. Green roofs represents a fundamental means of ecological compensation within the built environment, i.e. in highly altered and disturbed places by humans. In particular, green roofs for biodiversity (or biodiversity green roofs), being characterised by different but contiguous microhabitat (habitat mosaics or patches), can host several species with different mor- phological and functional traits (Brenneisen, 2003). The method known as the habitat template consists of choosing suitable plant species for green roofs from among the one that live in nature under similar conditions e.g. shallow and nutrient poor substrate, drought resistant (Lundholm, 2006). The phytosociological approach applied to green roofs considers the habitat analogue not only as a species pool, but also as a model to group plants in specific associations.
