Biodiversity on urban roofs

Green roofs improve air quality and reduce the urban heat island effect. But they’re also places that allow urban flora and fauna to flourish. In urban areas with lots of sealed surfaces, green roofs play a key role in maintaining and boosting biodiversity. They mirror the functions of natural habitats or stepping stone biotopes that have already been lost.

Waning urban biodiversity

As urban populations grow, widespread development of urban land is also intensifying at a fast rate. Rising urbanisation has a hugely negative impact on urban biodiversity and the ecosystem services it delivers.

The main cause is wide-scale soil sealing. The increase in impervious surfaces decreases the diversity of urban plants and natural habitats. At the same time, fragmentation of the urban landscape makes gene flow between populations more difficult, leading to a drop in urban biodiversity.

Graue Stadt - Fehlende Biodiversität in urbanen Zonen

Green roofs boost biodiversity

As part of the green infrastructure, green roofs can promote biodiversity in built-up areas by creating new vegetation structures and sources of food and habitats for flora and fauna. Known as stepping stone biotopes, they improve connectivity between different habitats and therefore urban biodiversity as well.

For a diverse range of animals and insects, lots of green roofs are an important source of food. One such example is wild herbs that attract a vast number of butterflies. As they provide plenty of nesting materials, a suitable habitat for wild bees can be created on green roofs.

A study in Basel on green-roof biodiversity found 79 species of beetle, 40 species of spider and some very rare species in the microhabitats of green roofs (Brenneisen 2006).

In particular, retention roofs are a superb habitat for flora and fauna due to the extra irrigation provided. This factor is crucial to mitigate the effects of drought, especially in the hot summer months. Irrigation improves conditions when plants are establishing themselves and provides the water for germination during droughts. The resulting rise in plant growth promotes biodiversity, as more diverse plants lead to more diverse habitats and therefore a greater range of species in the animal kingdom.

Green roofs and human beings’ health

Because of the ecosystem services they provide, incorporating green roofs into urban areas is good for people’s health and well-being. Green roofs can also reduce flooding, heat islands, and improve air quality. Consequently, all these factors equally help improve the health of the urban population.

Due to the evaporation that occurs, green roof vegetation can effectively reduce urban heat islands and the associated health risks. In addition to cooling urban spaces down, green roofs can also enhance the air quality by binding both pollutants in the air and particles of dust.

According to the study by Anderson et al. (2021), people’s mental health benefits if they have access to green roofs as recreational spaces in very built-up areas.

Therefore, as key elements of urban blue/green infrastructure, green roofs have the potential to benefit urban life, sustainability, subjective well-being, and biodiversity.

Fig. 1: How urban green spaces boost health; Ode Sang et al. 2022

Anderson, Vidya; Gough, William A.; Agic, Branka (2021): Nature-Based Equity: An Assessment of the Public Health Impacts of Green Infrastructure in Ontario Canada. In: International journal of environmental research and public health 18 (11). Retrieved here: Link

Brenneisen Stephan (2006): Space for urban wildlife: Designing green roofs as habitats in Switzerland. Urban Habitats 4: 27–36. Retrieved here: Link

List of figures
Ode Sang, Åsa; Thorpert, Petra; Fransson, Ann-Mari (2022): Planning, Designing, and Managing Green Roofs and Green Walls for Public Health – An Ecosystem Services Approach. In: Front. Ecol. Evol. 10, article 804500. Retrieved here: Link