Biodiversity in an urban setting: Arthropod abundance and diversity on an extensive green roof

Green roofs – building tops that are partially or completely covered in vegetation – have gained popularity to reduce heat, mitigate stormwater runoff, and filter pollutants. The ecology and biodiversity of green roofs, especially in the western high plains of the United States, is an emerging field. This ongoing observational biodiversity study helps in the understanding of what effect green roofs have on urban arthropods. The monitoring and assessment of arthropod biodiversity is part of an interdisciplinary Metropolitan State University of Denver study regarding the green roof ecosystem atop the Student Success Building. The two-year-old extensive sedum roof has four identified eco-zones; three vegetated zones with differing sun exposures, and one zone consisting of conventional rock roofing. We examined the arthropod fauna using multiple sampling methods on a regular schedule to determine changes in diversity throughout seasons and the differences in diversity between the existing eco-zones. The sampling methods utilized included active and passive traps, intended for an all-inclusive survey that accounted for diurnal and seasonal patterns. Active sampling methods included hand sampling and suction traps, and passive sampling methods included intercept traps, insect bowls and pitfall traps. The most commonly collected orders of Hexapods were Diptera, Hymenoptera, Thysanoptera, and Hemiptera. Overall abundance was higher on the vegetated roof surface than on the conventional roof surface, and included many beneficial arthropods, as well as those that contribute to soil enhancement.