Gardeners Have a Role in Boosting Pollinator Diversity in Dense Cities

A recent study published in the journal Urban Ecosystems by Vincent Zaninotto and colleagues highlights the potential for improving pollinator diversity even in highly urbanized environments. By focusing on the city of Paris, the researchers sought to understand the factors influencing insect pollinator communities in areas dominated by artificial habitats.

Pollinators, such as bees, butterflies, and other insects, play a vital role in maintaining the health of ecosystems and supporting agriculture. However, urbanization is often associated with declining pollinator diversity and abundance, as natural habitats are destroyed and replaced with impervious surfaces such as roads and buildings. This research aimed to investigate the drivers of pollinator diversity within an urban matrix and suggest strategies to promote pollinator health in urban environments.

The team monitored insect pollinator communities monthly from March to October over two years in 12 different green spaces in Paris. These spaces varied in size, management practices, and plant species, allowing the researchers to explore the effects of these factors on pollinator diversity. The study focused on four insect orders: Hymenoptera (bees and wasps), Diptera (flies), Lepidoptera (butterflies and moths), and Coleoptera (beetles).

The results showed that both pollinator abundance and species richness were positively correlated with green space size and flowering plant species richness. In contrast, they were negatively associated with surrounding impervious surfaces. The study also found that environmental features at both local and landscape scales influenced the composition and functional diversity of wild bee communities.

Interestingly, small and large bees responded differently to the proportion of impervious surfaces and plant species richness. Large-bodied bee species were negatively affected by impervious surfaces but strongly benefited from increased plant species richness. Moreover, sites with a majority of spontaneous plant species – those that grow without human intervention – had more functionally diverse bee communities. Oligolectic species, which are bees that specialize in collecting pollen from a narrow range of plants, were more likely to be found in these areas.

These findings are consistent with previous literature and can inform the design and management practices of urban green spaces to promote pollinator diversity and pollination function, even in dense urban environments like Paris. By increasing the size of green spaces, planting a diverse array of flowering plants, and allowing for spontaneous plant species to grow, city planners and landscape architects can help create urban havens for pollinators.

Zaninotto and colleagues say that when space is at a premium, as in a city centre, the most useful practical action is connecting green spaces with green corridors. The authors mention in their article that gardeners can play a part too in helping pollinators, both by adding specific plants to their garden and not evicting some uninvited guests: 

Our data confirm that the overall abundance and species richness of insect pollinators rely on the diversity of local plant resources. We recommend that gardeners plant a wide variety of entomogamous [insect-pollinated] plant species, paying particular attention to seasonal flowering successions. Indeed, as our approach spanned over most of the year (March to October), ensuring a sufficient floral display throughout seasons seems critical. Besides, our results suggest that native, spontaneous flora may be more valuable to sustain pollinator diversity. Such flora may be more suitable for specialist pollinators, including oligolectic bee species, thus contributing to functional pollinator diversity. Overall, we recommend reducing the frequency of mowing and maintaining or establishing wild patches of spontaneous plants to support insect pollinators in green spaces. At the city scale, the presence of lightly managed ruderal [wasteground] spaces would thereby not only host a diversity of pollinators but enhance all aspects of urban biodiversity.

Zaninotto et al. 2023

READ THE ARTICLE

Zaninotto, V., Fauviau, A. and Dajoz, I. (2023) “Diversity of greenspace design and management impacts pollinator communities in a densely urbanized landscape: the city of Paris, France,” Urban Ecosystems. Available at: https://doi.org/10.1007/s11252-023-01351-x.