Comparing arthropod communities on two types of extensive green roofs

Abstract

Extensive green roofs are said to increase local arthropod diversity in urban environments. Most roofs are dominated by either generalists or xerothermic species, as a result of their isolated locations and shallow substrate layers. We investigated whether biodiverse extensive green roofs (Sedum spp., forbs and grasses) attract more arthropod species than conventional extensive green roofs (only Sedum spp.) and differ in their respective community compositions. Six conventional and six biodiverse green roofs were sampled continuously for one year via pitfall traps. Ants, carabids and spiders were identified to the species level. We found 63 spider species, 47 ground beetle species and 22 ant species during our study. Spider communities were dominated by easily dispersible species of Linyphiidae, ground beetle communities by either eurytopic or xerothermic species, and ant communities by the synanthrope Lasius niger. While ant communities differed significantly between conventional and biodiverse roofs, no effect of roof type was observed for spider or ground beetle communities. We conclude that both types of green roof give similar results in the context of conserving urban arthropod diversity, at least for the taxa we investigated. In order to attract a wider variety of arthropods in urban areas we recommend the installation of green roofs that are specifically designed to increase biodiversity.