Greens up: vertical greenings to promote urban pollinators – a preliminary study from a Central European City

Abstract Urban expansion continues to impact natural landscapes and biodiversity, yet cities are implementing measures to mitigate some of these negative effects. One such measure is the use of vertical greenings, which aim to enhance urban ecosystems and support biodiversity. Given the limited knowledge of pollinators in these vertical green spaces, we conducted a pilot study in a Central European city (Vienna, Austria) focusing on butterfly and wild bee species richness and their interactions with foraging plants during the year 2022. In total, we recorded 32 wild bee species and eight butterfly species. Our results show that vertical greenings with high floral richness (i.e., comprising more than four flowering entomophilous plant species) supported significantly more wild bee ( p = 0.005) and butterfly ( p = 0.002) species compared to vertical greenings with low floral richness (i.e., comprising two or fewer flowering plant species). The majority of bee-plant interactions were observed on Nepeta faassenii , Sedum sp., and Parthenocissus quinquefolia , while most butterfly-plant interactions were observed on Nepeta faassenii . Implications for insect conservation: Our study demonstrates that vertical greenings may serve as valuable nectar and pollen sources in urban environments. However, their effectiveness most likely depends on floral diversity, which we observed to be, at least partly, influenced by the maintenance practices of the greenings.