Red and white clover provide food resources for honeybees and wild bees in urban environments

Pollination is a key ecological process both in wild plant species and in economically important crops. Global land use change and urbanization are known to alter plant-pollinator interactions, but our understanding of how the local (i.e. size of green area, food resource availability) and landscape (surrounding green area) context affect pollinators in urban landscapes remains understudied. We selected two co-occurring clover species, Trifolium pratense and T. repens to assess whether mixed stands of common wildflowers provide resources for a diverse pollinator assemblage by supporting differently adapted/specialized pollinator species. We further wanted to test how environmental factors (flower diversity, resource availability, size and percentage of green area) alter plant-pollinator interactions in urban environments. We studied the pollinator assemblage and visitation rate of pollinators in 1-m(2) plots in 21 green areas of different sizes in the city of Vienna (Austria). In addition, we assessed the surrounding landscape context by estimating the percentage of green area in perimeters of 100, 500 and 1000 m around each study plot and measured local flower resource availability. We found that proportions of pollinator taxa differed significantly between white and red clover, with T. repens mainly pollinated by Apis mellifera, and T. pratense primarily pollinated by different bumblebee species. Visitation frequency was positively correlated to local resource availability (number of anthetic Trifolium inflorescences in each plot), but independent of the surrounding landscape context (i.e. percentage of green area). We conclude that the establishment and maintenance even of small patches of different common wildflowers help maintain a diverse bee community in urban environments. Particularly large-flowered species may be important for supporting long-tongued, late emerging pollinators such as certain bumblebee species.