A survey of summer pollinator assemblies in two contiguous Richmond, Virginia (U.S.A.), urban green spaces

 By Ruppel & Trapp

A carder bee (Anthidium)

About 70% of the global human population is expected to reside in cities by the year 2050, further increasing our urban footprint and reducing wildlife resources. Green infrastructure incorporates natural elements into city spaces often heavily laden by concrete and can provide ecosystem resources for declining insects.  Pollinators, in particular, benefit from greater access to foraging rewards and nest sites. In this study, we surveyed two contiguous urban gardens which sit adjacent to substantial amounts of impervious surfaces, two active railroad tracks, and the Kanawha Canal in Richmond, Virginia (U.S.A). These gardens were planted with a preference toward Virginia-state native plants, and contain 70 unique species made up of flowering trees, shrubs and herbaceous perennials.

Our aim was to identify insects using the urban gardens for floral resources, like pollen and nectar. We surveyed floral visitor interactions on 19 plant species at Great Shiplock Park and the Low Line Gardens from June to August in 2023. Flower visiting insects were visually-identified in the field or via photography/specimen collection. Overall, 110 distinct floral visitors were observed over the ten weeks and categorized as a bee (25% of all observations), wasp (18%), butterfly/moth (16%), fly (15%), beetle, or true bug. We found that insect visitation varied by category across the surveyed plant species, and the two gardens hosted a broad range of both generalists and specialists. For example, the common eastern bumblebee (Bombus impatiens) was identified on all nineteen plant species. Meanwhile, many of the observed taxa were seen on four or fewer of the monitored plant species. Of the 11 bee species observed on four or fewer flowers were two rare bumblebee species, the golden northern bumblebee (Bombus fervidus) and southern plains bumblebee (Bombus fraternus), which were both recently recommended for federal protection.

The results of this survey provide a regional and seasonal perspective on urban green space ecosystem dynamics, and a reference that new green infrastructure projects can utilize. Our observations, especially for bees, were similar to another assessment recently conducted in the region. Furthermore, the outcome of this inventory can be used to assess impacts of urbanization on plant-pollinator interactions with response to pressures like climate change.

 

Read the scientific publication in JPE