Floral resources in four urban green spaces: an exploratory comparative case study of species composition, pollen, and nectar availability

Urban areas are expanding rapidly, increasing the need to integrate cities with high-quality green infrastructure. Pollination, a key plant–animal interaction, depends on the availability of adequate floral food rewards to sustain pollinator communities even within urbanized landscapes. This study assessed the availability of floral rewards across four representative urban green-space types under typical management conditions — ornamental plantings, intensively mown lawns, roadside verges, and a semi-natural urban green space. We found site-level differences in pollen availability and potential nectar supply, as well as in their seasonal dynamics. Maintained ornamental plantings supported overall floral resource availability and plant species diversity, whereas intensively mown lawns and the semi-natural urban green space were characterized by comparatively lower resource levels. Across sites, floral reward supply was strongly dominated by a limited number of plant species, most notably members of the Asteraceae family. Both pollen availability and potential nectar supply declined toward the end of the growing season, indicating seasonal gaps in floral resource provision. Our results further indicate that urban green spaces designed primarily for one functional group may not automatically provide sufficient floral resources for pollinators, and that the dominance of plant species offering accessible rewards to a wide range of pollinator groups is crucial for multifunctional urban landscapes. Strategic plant selection and management can therefore play a critical role in sustaining pollinator resources throughout the vegetative season in urban landscapes.