A comparison of 3 types of green roof as habitats for arthropods

- Green roofs host diverse arthropod communities according to their vegetal structures.
- Arbustive roofs exhibit a higher species richness than muscinal (moss/sedum) roofs.
- Arthropods are more abundant on arbustive roofs than on herbaceous and muscinal (moss/sedum) roofs.
- The taxonomic composition of spider communities is shaped by the green roof type.
- The functional composition of hymenoteran communities is shaped by the potential surrounding habitats.

In an inexorably urbanizing world, green roofs could be an interesting tool to conciliate the greening of cities with ecological services. Studies on a large number of sites are necessary to understand the importance of environmental variables, especially how the type of vegetation affects the green roof biodiversity.We sampled several arthropods (spiders, true bugs, beetles and hymenopterans) from buildings covered by green roofs in 115 sites across northern France. We considered 3 types of green roofs with diverse vegetal structures: muscinal (moss/sedum - M) roofs, herbaceous (moss/sedum and meadow - H) roofs and arbustive (moss/sedum, meadow and shrub - A) roofs.The species richness and the abundance of most of the taxa were significantly higher on A roofs, which displayed more complex vegetation. Predominantly common species comprised the arthropod communities. However, xero-thermophilic species and species from sandy and rocky habitats were also present because green roofs could serve as habitat analogs of those dry natural habitats. Except for hymenopterans, we did not observe a difference in the functional composition of communities; however, the taxonomic composition of spider communities was significantly affected by the green roof type. The surrounding environment and other local variables exhibited a minor influence on the composition, abundance and richness of the arthropods. We revealed a major role for the vegetal structures in arthropod communities and the ability of green roofs to enhance urban biodiversity.