Environmental factors influencing ground-nesting bee communities in an urban landscape: implications for conservation

Habitat loss and degradation of nesting habitats due to agricultural and urban development is considered one of the key factors causing pollinator decline worldwide. Nesting habitat requirements and availability is a strong determinant to which wild bee species are prevailing in urban spaces and knowledge of habitat requirements is therefore fundamental for successful conservation management. Although urban environments can host relatively diverse wild bee communities, ground-nesting bees and associated cleptoparasitic bees are disadvantaged, primarily due to a scarcity of suitable nesting resources. Further, conservation efforts for wild bee habitat (re)creation are largely focused on aerial nesters, despite the proportionally greater diversity and higher vulnerability of ground-nesting bees. The aim of this study was to investigate how environmental factors, including the age and size of sand patches, sand grain size, soil temperature, and the proportion of ground litter-cover vs. bare ground, have shaped ground-nesting bee community structure in an urban landscape. This was done by evaluating wild bee diversity and abundance across various sites with a range of qualities in Uppsala, Sweden. This study revealed a drastic 85% loss of suitable sandy habitat over a 75-year period due to urbanization. Based on the results of this study, we recommend a conservation approach for urban developers to lessen the negative impacts of urbanization on wild bee diversity and abundance. This includes the establishment of numerous bare ground sandy sites with medium size sand grain, and periodical management of vegetation to sustain bare sandy soil patches.