Habitat connectivity and local conditions shape taxonomic and functional diversity of arthropods on green roofs.
Increasing development of urban environments creates high pressure on green spaces with potential negative impacts on biodiversity and ecosystem services. There is growing evidence that green roofs - rooftops covered with vegetation - can contribute mitigate the loss of urban green spaces by providing new habitats for numerous arthropod species. Whether green roofs can contribute to enhance taxonomic and functional diversity and increase connectivity across urbanized areas remains, however, largely unknown. Furthermore, only limited information is available on how environmental conditions shape green roof arthropod communities. We investigated the community composition of arthropods (Apidae, Curculionidae, Araneae and Carabidae) on 40 green roofs and 40 green sites at ground level in the city of Zurich, Switzerland. We assessed how the site's environmental variables (such as area, height, vegetation, substrate and connectivity among sites) affect species richness and functional diversity using generalized linear models. We used an extension of co-inertia analysis (RLQ) and fourth-corner analysis to highlight the mechanism underlying community assemblages across taxonomic groups on green roof and ground communities. Species richness was higher at ground-level sites, while no difference in functional diversity was found between green roofs and ground sites. Green roof arthropod diversity increased with higher connectivity and plant species richness, irrespective of substrate depth, height and area of green roofs. The species trait analysis reviewed the mechanisms related to the environmental predictors that shape the species assemblages of the different taxa at ground and roof sites. Our study shows the important contribution of green roofs in maintaining high functional diversity of arthropod communities across different taxonomic groups, despite their lower species richness compared with ground sites. Species communities on green roofs revealed to be characterized by specific trait assemblages. The study also provides details on the environmental conditions that influence arthropod diversity and gives new perspectives on how the design of green roofs can be improved to increase their ecological value. Furthermore, the study highlights the importance of integrating green roofs in planning policies which aim to enhance urban habitat connectivity.
Biodiversity and Conservation Biology, Swiss Federal Research Institute WSL, Birmensdorf, Switzerland.|Institute of Terrestrial Ecosystems, Ecosystem Management, ETH Zürich, Zürich, Switzerland.
Sonja
0000-0002-0080-6106
S
Braaker
Biodiversity and Conservation Biology, Swiss Federal Research Institute WSL, Birmensdorf, Switzerland.
Martin Karl
MK
Obrist
Institute of Terrestrial Ecosystems, Ecosystem Management, ETH Zürich, Zürich, Switzerland.
Jaboury
J
Ghazoul
Biodiversity and Conservation Biology, Swiss Federal Research Institute WSL, Birmensdorf, Switzerland.
Marco
M
Moretti
D000531:Altitude; D000818:Animals; D001516:Bees / Q000502:physiology*; D044822:Biodiversity; D002947:Cities; D001517:Coleoptera / Q000502:physiology*; D017753:Ecosystem; D013112:Spiders / Q000502:physiology*; D013557:Switzerland
bees; brownfield; community assemblages; functional trait; ground beetles; insects; ruderal vegetation; spiders; vegetated roof; weevils