Biochar amendments increase diversity of epigeic green roof arthropods

Biochar amendments to green roof substrates have been promoted as benefitting green roof performance through improved water and nutrient retention. Biochar amendments might specifically increase the abundance and diversity of epigeic invertebrates – i.e., invertebrates inhabiting the soil surface – by enhancing substrate water retention, plant cover, and microbial biomass. We examined effects of biochar amendments on epigeic green roof invertebrates based on a multi-year factorial experiment involving 5% biochar additions to an organic green roof substrate with two vegetation types: a sedum mat and a native plant mixture including forbs and grasses. Invertebrate communities were also sampled in nearby ground-level vegetation. Biochar-amended plots showed an increase in both overall invertebrate abundance and diversity (species richness and Shannon index) compared to controls. In addition, biochar amendments altered invertebrate community composition, with a number of native arthropod species showing substantial increases. Native vegetation increased the overall abundance, but not diversity, of native arthropods sampled compared to sedum mats. The epigeic arthropod community on the green roof substrates showed lower overall abundance than nearby ground sites but was distinct from the ground community and rich in native species. We conclude that biochar amendments can substantially benefit invertebrate abundance and diversity in green roof systems and should be considered as part of an integrated strategy to enhance ecosystem functions – including biodiversity habitat provision – of urban green infrastructure.