Are parks as favourable habitats for wild bees as wastelands in watercourse valleys of a large city?

Abstract

Because of the growing population density and rate of urban development, the question of biodiversity conservation in cities and towns is increasingly important. In general, urban environments provide attractive habitats for a diversity of wild bees, but different types of urban habitats can have different effects on these pollinating insects. In this study, we compared the attractiveness of two different urban habitat types – parks (10 sites) and wastelands (10 sites) located in river and canal valleys in Bydgoszcz (northern Poland) – with respect to abundance, species richness, species composition, and functional trait composition of wild bees. We hypothesized that urban wastelands are more attractive to wild bees than urban parks are. Urban wastelands were characterized by higher abundance and species richness of wild bees compared to urban parks. When habitat type was the only predictor, nonlinearity of wild bee abundance and species richness was significant exclusively for wastelands. Overall, both wild bee abundance and species richness depended on the percentage of total bee food plant coverage, regardless of habitat type. Wild bee community composition also responded significantly to the percentage of total bee food plant coverage. Local and landscape features of the green spaces affected the functional traits of the wild bees recorded there. These findings reveal that formal green spaces, such as managed parks, are not sufficient to conserve wild bee resources in urban environments in river and canal valleys. In contrast, high-quality informal urban green spaces, such as urban wastelands, can promote abundant and rich wild bee communities. Thus it is crucial to strive for appreciation and protection of this persistently overlooked category of urban green spaces.