The construction of vegetated stormwater control areas, i.e. biocells or rain gardens, is becoming increasingly common in urban areas. Biocells provide the combined benefit of attenuating peak stormwater flows while meeting urban landscape design requirements. Though biocells represent a movement toward designing more “natural” urban structures, the effectiveness of biocells in promoting urban biodiversity and ecosystem functions has yet to be examined. The goal of this study is to determine how environmental factors of biocells, such as temperature, species and structural complexity of plants, and soil moisture, affect the insects and wildlife that live or forage there. In a preliminary study, I observed the overall insect community of 8 biocells on North Carolina State University’s campus by identifying scale insects on twigs cut from red-twigged dogwoods and by identifying insects collected from sticky cards. Insect abundance was compared to site temperature and soil moisture. Further experiments will examine bioindicator arthropods in the soil litter (e.g. carabid beetles, isopods) using Winkler extractors on 15 sites. In addition, abundance and diversity of insect-eating birds will be recorded at each biocell in order to obtain a link between biocell design or environmental factors and the abundance of insects and their predators.
Results/Conclusions
Though no direct correlations have been found between environmental factors and insect abundance, the collected data provides a generalization of the relative susceptibility of biocell plants to scale insect infestation and of the biocell’s role as an insect attractor. Certain insects were found to be highly abundant at most sites (e.g. parasitoid wasps, aphids) while others had high abundances at a few sites (e.g. gloomy scales, sharpshooters). Since parasitoid wasps are commonly used as biocontrol for insect pests, this finding could strengthen support for the ecological importance of biocells in maintaining pest control in the urban landscape. Mosquitoes were not found at any sights, confirming that the biocells’ high drainage rates do not promote mosquito breeding grounds. Mosquitoes are a common concern when weighing the pros and cons of stormwater control structures, so this finding could support biocells as a more beneficial design compared to others (e.g. wet detention or wetlands). If the experiments yet to be conducted support an existing interaction between insects and birds in biocells, this link will further support the ecological benefit of biocells.