Brown/biodiverse roofs: a conservation action for threatened brownfields to support urban biodiversity

Despite the need to restore urban green spaces, there are rarely enough open spaces due to urban densification. Thus, rooftops of buildings, which had not previously been regarded as spaces for planting of vegetation, have been utilised as a type of open space, and green roofing has become one of the rapidly developing fields of urban ecological engineering. However, current green roof approaches each have negative aspects in terms of enhancing urban biodiversity: intensive roofs in urban areas cannot contribute a large amount of green area, and extensive roofs cannot create high-quality green areas. In this report, we outline brown/biodiverse roofing in the UK, which is a relatively new type of extensive roofing used to provide brownfield wildlife with mimic brownfields. Brownfield refers to land that was previously developed for housing or industry but has since been abandoned and recolonised by different ecological assemblages. Brownfields provide habitat conditions similar to more natural habitats, and they can help maintain populations of some rare species. From the 1980s to the present day, the UK government has set a target of building 60% of new dwellings on brownfields. One of the most successful strategies that has been employed by the third constituency in its efforts to campaign for urban biodiversity and brownfield conservation has been to compromise with developers of brownfields and to persuade them to install wildlife-friendly mitigation technologies on roofs. This is the origin of brown/biodiverse roofs, which benefit from techniques that offer diverse habitats under severe conditions of thin substrate layer.