Local terrestrial biodiversity impacts in life cycle assessment: A case study of sedum roofs in London, UK

Urban development is a key driver of global biodiversity loss. "Green" infrastructure is integrated to offset some impacts of development on ecosystem quality by supporting urban biodiversity, a prominent example being green roofs. The effects of green infrastructures on urban biodiversity are not well understood and poorly included in life cycle assessment (LCA) methodology. Here, we present a novel methodology that quantifies the local impact of green infrastructures on terrestrial biodiversity-demonstrated here for sedum roofs in London, UK-and integrates within LCA. It relates energy provision by plants to the metabolic requirements of animals to determine what species richness (number of species) and species abundance (number of individuals) are supported. We demonstrate this methodology using a case study, comparing the life cycle impact of developing 18 buildings, with either asphalt concrete or sedum roofs, on ecosystem quality. We found the sedum roofs (0.018 km2) support 53 species (673 individuals), equivalent to 1.3% of the development's life cycle impacts on ecosystem quality. Complete offsetting requires considerable reduction in transport use throughout the development's lifetime, and lower environmental impact material selection during construction (contributing 98% and 2%, respectively). The results indicate sedum roofs offer minor impact mitigation capacities in the context of urban development, and this capacity is limited for all green infrastructures by species richness in local species pools. This paper demonstrates the potential and limitations of quantifying terrestrial biodiversity offsets offered by green infrastructures alongside urbanization, and the need for realistic expectations of what role it might play in sustainable urban design.