Floral resource availability and honeybee flower visitations in Oslo, Norway

Urban green infrastructure can provide important habitats for pollinators
and support urban ecosystem services. Therefore, these areas must be
managed to maximize biodiversity and density of pollinating insects. We
used DNA metabarcoding to study honeybee pollen resource use over time and
space in the city of Oslo, Norway, and to assess the role of green
infrastructure as a resource for pollinators and the services they
generate. Urban honeybees used diverse pollen resources throughout their
active season. There was considerable seasonal turnover in pollen resource
use that reflected flowering phenology. Non-native plants (including
invasive species) were an important resource early in the season but were
replaced by native plants later in the season. Hive location was not
strongly correlated with resource use, likely indicating effective
long-distance foraging in the fragmented urban landscape. However, flower
visitation rates and floral resource density in public urban green spaces
were coupled with pollen use. Honeybees collected pollen from a small
number of preferred species but also visited other species, likely for
nectar. To preserve pollinator services, urban planning should consider
flower resource management, with particular focus on planting native
species that can act as early season resources for bees. Public campaigns
and other incentive mechanisms to promote the cultivation of native plants
that are resources for pollinators and the protection of urban
semi-natural habitats have the potential to enhance the value of green
infrastructure to support urban pollinators and pollination services.