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Green roofs provide additional habitats
July 23, 2026 |
Green roofs are increasingly recognised as novel habitats and, according to a study by the aquatic research institute Eawag together with WSL, can support diverse species communities. According to the researchers, only 10% of the species found on the ground and on green roofs overlap. This means that greening façades and roofs does not simply serve to extend existing habitats but enriches biodiversity within cities with new communities.
Green roofs can become a trap
Yet there are still hurdles for the inhabitants up high. Through analysis of eDNA (more on this here), the researchers found that not only the variety of species but also the food web on roofs differs significantly from that on the ground. Species diversity is also more limited on the roofs than in habitats close to the ground. “This means that the food web on green roofs is more vulnerable to secondary extinction events,” explains Kilian Perrelet who conducted both studies as part of his PhD under the supervision of Lauren Cook and Florian Altermatt (both at Eawag) and Marco Moretti (WSL).
According to Perrelet this vulnerability to such chain reactions within the food web is because more predators are found on green roofs than organisms that feed on organic soil matter – such as earthworms or springtails. In other words, many of the inhabitants of a green roof could eventually run out of food, especially those at the top of the food web. Environmental conditions are also more challenging on green roofs; higher temperatures, scarcer water supplies, and limited organic matter inputs, like fewer plants or very mineral substrate, can cause problems. This raises the question of whether green roofs can function as sustainable habitats or whether they are, in fact, ecological traps for those species that find it difficult to move around.
Sustainable planning and design
Perrelet, however, is optimistic: “There are design measures for green roofs that can promote biodiversity across the vast majority of species detected.” Older roofs with deeper substrates may harbour more diverse communities, especially species forming the foundation of the food web. As a result, such roofs show greater resilience to secondary extinctions than newer green roofs with shallow substrates. In the planning phase, therefore, priority should be given to increasing the substrate depth. High vegetation cover also has a positive effect: in other words, the abundant planting of the area, ideally with substrates rich in organic matter.
Further studies will be needed to assess whether habitats above the city can be promoted through additional measures. For example, by planting a variety of trees and shrubs or incorporating water features. “Collaboration with architects and engineers is also crucial for the future of these habitats,” says Perrelet. Ideally, this would be done in the planning phase, as renovation of existing building can be very expensive. It would also be beneficial for biodiversity in cities if all these currently separate habitats could be connected, for example via terraces or ramps. As a result, green roofs would no longer be self-contained habitats at the mercy of external influences but could instead integrate naturally into a vibrant and sustainable ecosystem.
Green roofs differ from ground-level habitats in terms of species diversity. This can – if supported by the right measures – complement biodiversity in cities.
Blue-green infrastructure
Blue-green infrastructure (BGI) is an integrated, nature-based approach to urban planning. The concept combines the natural water cycle (water bodies, infiltration areas) with green elements such as green spaces, green roofs and trees, in order to manage water sustainably and promote biodiversity. In contrast to traditional, grey infrastructure (concrete channels and pipes), BGI utilises natural processes to absorb, store and filter rainwater. This reduces the risk of flooding, improves water quality and, at the same time, cools the city. Researchers at Eawag are conducting interdisciplinary projects to investigate how effective blue-green infrastructure can make our cities more climate-resilient and liveable.
Cover picture: Green roofs differ from ground-level habitats in terms of biodiversity. This can help to boost biodiversity in cities. (Photo: Kilian Perrelet, Eawag)
