Do green roofs help urban biodiversity conservation?
Green roofs are novel ecosystems that are increasingly common in cities. While their hydrologic and energy saving benefits are well-established, green roofs have also been proposed as having significant value for conserving biodiversity. We evaluate six hypotheses that describe the purported biodiversity conservation benefits of green roofs. Green roofs largely support generalist species particularly insects, but their conservation value for rare taxa, and other taxonomic groups especially vertebrates, is poorly documented. Further, their ability to replicate biotic communities in the context of ecological restoration is largely untested, as is their potential to connect ground-level habitats. Synthesis and applications. Given the evidence, green roof proponents should use restraint in claiming conservation benefits and it is premature for policymakers to consider green roofs equivalent to ground-level urban habitats. Ecologists need to work with the industry to evaluate green roof biodiversity and help design green roofs based on ecological principles to maximize biodiversity gains.