Distribution of flowering resources across urban neighborhoods and implications for pollinators

Background/Question/Methods

 Many urban plant species are actively planted for aesthetic purposes, making the distribution of floral resources dependent on human-mediated factors. The high level of disturbance in cities could alter plant community composition and affect resource availability for pollinators. We examine if plant characteristics, including ornamental or weedy and perennial or annual, are influenced by socioeconomic factors. We recorded flowers along 30 neighborhood block transects in Chicago, IL over two summers, and pooled flowers at the genus level for analysis. Midwestern (USA) cities tend to have a gradient of income and population density across neighborhoods. We selected sites from neighborhoods of varying socioeconomic characteristics and use multivariate statistics to investigate if demographic patterns of urban residents drive community level distribution of plants. We hypothesized that increased plant abundance in wealthier and denser neighborhoods will lead to a shift in the characteristics of flowers and visiting pollinators. A second objective of our research is to examine the stability of the plant community across years.

Results/Conclusions

Urban plant species tended to be perennial, ornamental, and non-native. Weedy species including white clover and pepperweed accounted for >60% flowers on neighborhood transects. There was greater diversity in ornamental flower species, but Rose and Petunia, the most commonly occurring ornamental flowers, accounted for no greater than 6% and 5.5% of ornamental flower abundance, respectively. We identified income as significant predictor for several plant characteristics with showier flowers and inflorescences more common in wealthier neighborhoods. Most pollinator visits were recorded on ornamental species, but several weedy plants support wild bees. Interestingly, we observed a pattern of ornamental flowers species richness plateauing at intermediate levels of household income and residential parcels (R²=0.32, GAM). However, several weedy, unmanaged plants were important resources for wild bees.  Community composition was significantly different between years (rho= 0.623, P=0.001), indicating a high level of turnover in abundance. Our results suggest a divergence in resources between wealthier, densely populated neighborhoods and poorer neighborhoods. This indicates that urban residents’ decisions in plantings communities is likely to affect populations of pollinators and nectar-visiting insects.