Supporting wild bees on green roofs and green walls : the importance of incentives from Swedish municipalities

Abstract: The importance of pollinators in urban areas have become a topic of current interest with increasing urbanisation. The current trend of urbanisation, e.g., tall buildings, concrete and densification, has forced green structures to adapt to the changes, resulting in biodiversity loss. As urbanisation continues, cities will continue to expand and thereby, it is crucial to halt the loss of biodiversity. A solution to tackle the limited space has been the implementation of green roofs and green walls. With the promising opportunities that emerged with the development of green roofs and living walls, this study aimed to investigate how the habitat requirements of wild bees could improve on these constructions. The study conducted a literature review about wild bees and projects focusing on wild bees from municipalities in Sweden. Additionally, lists (Tab. 1-6) of attractive plants to wild bees were created to improve habitat requirements. The study results indicate that preserving wild bees requires an interdisciplinary approach as multiple factors should be considered. Although the literature review results have shown that green roofs can effectively support biodiversity, uncertainties of the effectiveness of supporting biodiversity remain on green walls. The compiled lists of plants suitable for semi-extensive green roofs and wild bees is based on literature and all plants have not been tested in practice; therefore, it should be used as a guideline to reference/experiment. The study results also showed successful biodiversity preservation projects from municipalities, indicating that the cooperation and incentives from planners, the public and municipalities are valuable to halt the loss. Green roofs and green living walls are merely a complement to further enhance the existing green structures for wild bees. Urban areas are merely one of the habitats for wild bees and cannot replace their natural habitats.