Ground beetle (Coleoptera: Carabidae) communities on green roofs in Switzerland: synthesis and perspectives

Green roofs have recently gained recognition for their potential contribution to urban ecosystems by providing, among other services, habitat for plants and animals, and stepping stones for mobile organisms, thereby enhancing permeability among habitat patches across densely built cities. In Switzerland, investigations over the past 20 years on more than one hundred distinct green roofs across six cities have provided an unprecedented dataset on ground beetles, albeit with information that is scattered across unpublished reports and local databases. We present here for the first time a synthesis of the state of knowledge of ground beetle communities from green roofs in Switzerland. We describe 91 ground beetles species (19,428 individuals) and highlight patterns of species occurrence and composition across green roofs and cities. Most of the roofs host ground beetle communities dominated by five common mobile species with quite diversified ecological requirements. In addition, we observed nine species (10% of all species collected) that are conservation concerns in Switzerland and Central Europe as well as numerous stenotopic species (from grasslands and pioneer vegetation). This indicates that, besides sustaining local populations of common species, green roofs can also offer suitable ecological conditions of high conservation interest. We suggest both improving the design of green roofs (composition and configuration of vegetation, as well as soil depth and substrate composition) to increase their ecological value for species with the most different ecological needs, and to integrate green roofs into urban planning to make them more efficient as biodiversity supports.