The role of forests and large urban parks in sustain pollinator diversity and efficiency

Human activities have significantly shaped pollinator biodiversity, but sometimes urban environments offer opportunities as refuges for pollinators and large urban parks, having diverse habitats, could serve as both refuges and sources of biodiversity. This study, conducted under the National Biodiversity Future Center initiative on urban biodiversity, assesses the relationship between the pollination ecosystem service and urban greening actions. Relationships between forest spatial characteristics and pollinator abundances across an urbanization gradient and pollinator efficiency near old urban forests were tested. The landscape analysis examines forest size and fragmentation in relation to the pan-trapping of wild bees and beetles in 2019 and 2020. In Milan's urban parks, flower-visiting bees and beetle sampling was conducted between May and July 2021 along fixed transects using hand nets. Flower visitors were washed, and their pollen was counted with image analyses. The study also evaluated the presence and quantity of available wood for wood-nesting pollinators, considering different categories, such as decaying and non-decaying logs, wood on the ground, and standing trees of varying lengths. The results indicated direct relationships between forest patches and the amount of pollinators, emphasizing the importance of forest fragments. The pollen analysis demonstrates that traits such as body size and dependency on wood positively influence pollen load, clarifying the importance of forest management for the pollination service. Therefore, it is necessary to manage and maintain urban green spaces as pollinator refuges while sourcing areas that ensure the stability and diversity of pollinator communities.