The effect of urban green roof design on beetle biodiversity

The value of urban green spaces to biodiversity conservation depends on the design and management. The importance of habitat quality and complexity to species diversity has led to the suggestion that habitat design elements—varied substrate depth, greater plant diversity, logs or stones—would support invertebrate diversity on green roofs. To evaluate this possibility, we conducted pit-fall trap sampling on three green roofs of simple design (intended primarily for stormwater management), three habitat roofs, and five ground-level green spaces, in the Portland, Oregon metropolitan area. Beetles (Coleoptera) were sampled as representatives of total invertebrate diversity. Diversity was compared using sample coverage and Hill numbers to account for differences in sample intensity and fundamental differences in species diversity. Both habitat roofs and ground sites consisted of just over 20% native species, while stormwater roofs had about 5% native species, all of which were considered pests. We collected a greater abundance of beetles on the ground compared to roof sites like others have shown. However, when sample completeness is taken into account, habitat roofs had greater Shannon diversity compared to both ground and stormwater roof sites. Habitat roofs had the fewest dominant species representing 5% or more of total abundance, but also the lowest percent of species represented by singletons (27%). These results indicate that green roofs can support different beetle communities compared to those present at ground-level urban green spaces; our results also support previous findings that biodiverse design can reliably increase green roof diversity compared to more simply designed roofs.