Butterflies, tallgrass prairie, and green roofs

Abstract

As pollinators continue to decrease across the United States, it is becoming more important to understand how this trend can be reversed. Cities, which have typically eliminated and fragmented pollinator habitat, may be able to utilize rooftops for the benefit of pollinators. The Memorial Stadium green roofs at Kansas State University are rooftops previously used as stadium seating, portions of which have recently been converted to native prairie vegetation. I evaluated the effectiveness of these green roofs as pollinator habitat in an urban context by comparing butterfly communities of the green roofs to those in an urban native prairie at Warner Park in Manhattan, Kansas, and a protected tallgrass prairie at the Konza Prairie Biological Station, approximately 10 km south of Manhattan, Kansas. I assessed the influence of on-site vegetation composition on butterfly species richness, distribution, behavior, and abundance. I employed a modified Pollard walk, plant composition sampling, and mapping of spatial distribution of vegetation used by individual butterflies with a GPS unit.

Initial findings suggest that green roofs can provide urban habitat for butterflies. Indeed, butterfly abundance and mean species richness were greater at the Memorial Stadium than at either native prairie. However, while the green roofs support many species of butterflies, tallgrass prairie specialist species that were seen in the native prairie sites, such as the regal fritillary, were not observed using the green roofs. Butterfly behavior also varied between sites: butterflies using the stadium were predominately foraging, whereas butterflies at native prairie sites were flying through and not interacting with the plants. While plant species interactions with butterflies and links per species were greatest at Memorial Stadium, nestedness was lowest at this site. This study not only suggests that green roofs can compensate for lost pollinator habitat in urban areas, but by examining the effects of vegetation composition and structure as well as local land cover on butterfly abundance and behavior, it has important implications for the design and management of green roofs as urban butterfly habitat.