Green roofs may help restore the imbalance of the urban ecosystem by providing habitat within the urban environment for the coexistence of plants, vertebrates and invertebrate animal species, some of which may be rare or endangered. In fact, green roofs are often inhabited by various insects, spiders and birds.
Due that green roof design in term of biodiversity should be understood as a continuum of ecosystem around the city, the method to identify and value species to be taken into account should be based in the identification of this existing ecosystems and its trophic species, which are a scientific grouping of organisms according to their shared trophic (feeding) positions in a food web or food chain.
Trophic species have identical prey and a shared set of predators in the food web. This means that members of a trophic species share many of the same kinds of ecological functions. The category may include species of plant, animal, a combination of plant and animal, and biological stages of an organism.
The trophic species must be identified with support of experts in biology, birdwatchers, naturalist, veterinarians, public servants of maintenance services of local public parks, etc. The aim is to create a list of species that can alive in our green roof: detritivores, mushrooms, insects, plants, birds, etc. and, also, identify in our list the behaviour of each specie in order to know how to attract them to live in our green roof. The model of annotation could be similar as it is made by birdwatchers in their observations rounds.