Large cities are often perceived as concrete spaces disconnected from nature; however, they harbor an unsuspected biodiversity. Gardens, wastelands, urban parks, and green roofs are all refuges for fauna and flora that, despite major constraints, adapt and contribute to urban ecosystems. In the context of environmental crisis and adaptation to climate change, urban biodiversity appears as a key lever to strengthen the resilience of cities.
Interview conducted by: Justine Viros - Scientist specializing in environmental transition, Mediterranean forest, and chemical interactions between forest and atmosphere in the context of climate change.
The scientific perspective of: Magali Deschamps Cottin, teacher-researcher at Aix-Marseille University, an ecologist specializing in Lepidoptera or Butterflies (entomologist) and an expert in urban ecology, focuses on the dynamics of animal communities in anthropized ecosystems and has been working for several years to better understand and enhance this nature in the city. Her research shows that appropriate management of existing green spaces and the development of new biodiversity areas can promote the presence of essential species while improving the living environment for residents.
A biodiversity under pressure
Unlike natural ecosystems, urban biodiversity is subject to specific constraints such as habitat fragmentation due to soil artificialization, urban densification, and the disappearance of ecological continuities. There is also the intensive management of green spaces, with overly frequent mowing, the use of pesticides (which is becoming less relevant thanks to the passing of the Labbé Law since 2022 (1)), or the planting of exotic plants unsuitable for local insects. Finally, one of the major constraints of urbanized spaces for biodiversity is also light and noise pollution, disrupting the biological cycles of nocturnal species. (2)
Despite these challenges, many species manage to adapt and coexist in the city. This includes not only pigeons and rats but also a diversity of birds, pollinating insects, Lepidoptera (butterflies), and small mammals. Day-flying butterflies, for example, are particularly impacted by urbanization. The doctoral work of Marie-Hélène Lisée, defended in 2011 under the supervision of Magali Deschamps Cottin, shows that their populations decline as one approaches the urban center, with a loss of typically Mediterranean species. This loss is likely caused by physical barriers preventing their movement, as well as the disappearance of native plants from the Mediterranean ecosystem that are necessary for the feeding of typically Mediterranean butterflies, mainly during their caterpillar stage, thus blocking their ability to complete their life cycle. (3)
Thus, to promote biodiversity in the city, it is essential to rethink the management of green spaces. This concerns public parks and gardens, but also private gardens, urban wastelands, and green infrastructures. (4, 5)
Private gardens, although fragmented, represent a significant part of the vegetated area of cities, particularly found in islands between downtown buildings. By reducing mowing, promoting local plants, and leaving grassy areas, they could become true refuges for pollinators.
Urban wastelands, on the other hand, are often seen as plots waiting for construction, but they are actually reservoirs of biodiversity. Their spontaneous vegetation attracts many insects and small vertebrates. Projects for "urban nature reserves" are emerging to preserve these spaces while making them accessible to residents.
Finally, green roofs and walls sometimes appear as promising solutions to compensate for the disappearance of natural habitats. However, their implementation requires thorough consideration, particularly regarding the selection of plants suited to local conditions and water management, especially in a Mediterranean climate. By drawing inspiration from bio-inspired models and selecting adapted species, it is possible to reconcile aesthetics, ecological resilience, and attractiveness for local fauna. Magali Deschamps Cottin has notably participated in the development and implementation of monitoring protocols for a 5000m² green roof in the heart of the Vauban district of Marseille on the roof of the large water reservoir of Lacédémone, for which the results are promising and will be showcased in 2025.
Urban biodiversity: a key issue for the future of cities
Beyond the ecological question, nature in the city has a direct impact on the well-being of residents. A city that is too mineral intensifies the effects of urban heat islands, while vegetation cools the atmosphere and improves quality of life. Rediscovering urban biodiversity also means recognizing its fundamental role for our physical and mental health.
Today, the question is no longer whether to integrate biodiversity into the city, but how to do it intelligently (6). It is not enough to multiply green spaces; they must be designed ecologically and functionally, taking into account interactions between species, local specificities, and in an interdisciplinary manner. In this context, the research project Trajectoires (funded by the Mediterranean Institute for Environmental Transition) in which LPED participates aims, on one hand, to identify the areas richest in biodiversity in the city and to develop "naturalness" indicators to take this dimension into account in projects. And on the other hand, through an interdisciplinary approach (socio-urbanistic & ecological), to question the trajectories of urban wastelands in a context of urban development by posing the question of a common good. This tool should help guide public policies to effectively integrate biodiversity into their planning strategies.
One of the major obstacles to the preservation of urban biodiversity in Marseille is the fragmentation of responsibilities. Currently, municipal parks, wastelands, and private gardens are managed by different entities, complicating the establishment of ecological corridors that allow species to move. Better coordination among stakeholders (local authorities, urban planners, citizens) is necessary to ensure coherent and effective management of green spaces. Finally, the design of urban green spaces should not only meet aesthetic or practical criteria. The challenge is to integrate the specific needs of local species, avoiding, for example, introducing too many exotic plants that, while flowering and drought-resistant or easy to maintain, do not feed caterpillars or other insects; an ecological balance must be sought/found in the plant palettes.
Fortunately, thanks to scientific research and local initiatives, a new urban model is emerging: that of a city where nature takes its place alongside residents, fostering a sustainable ecological transition that benefits everyone. The cities of tomorrow will be those that can reconcile urban planning and biodiversity. Because beyond the ecological challenge, preserved nature in the city also contributes to the well-being of residents, climate regulation, and the resilience of territories in the face of global changes.
Biographies
Magali Deschamps Cottin – Teacher-researcher at LPED (Laboratory of Populations, Environment, Development). An ecologist, trained as an entomologist, specializing in urban ecology, she focuses on the dynamics of animal communities in anthropized ecosystems by studying the mechanisms of their maintenance or colonization in relation to the management and naturalness of these spaces. Her research is primarily conducted in interdisciplinary collaboration with sociologists, geographers, and urban planners in partnership with managers of urbanized spaces. She was instrumental in the creation of the Urban Butterfly Park project.
Justine Viros - Scientist specializing in environmental transition, Mediterranean forest, and chemical interactions between forest and atmosphere in the context of climate change. She currently holds a position as a Research Engineer within the Interdisciplinarity mission at Aix-Marseille University, where she is responsible for development for the Neede Méditerranée association. She notably participated in writing the application of Aix-Marseille University in partnership with Neede for the creation of a UNESCO chair titled “Education for Environmental Transition in the Mediterranean.”
Sources
(1) Labbé Law 2022- https://draaf.occitanie.agriculture.gouv.fr/loi-labbe-application-extension-a-compter-du-1er-juillet-2022-a7043.html
(2) Badiane, A., Ropars, L., Flacher, F. et al. Urbanization impacts the diversity, coloration, and body size of wild bees in a Mediterranean city. Reg Environ Change 24, 41 (2024). https://doi.org/10.1007/s10113-024-02199-3
(3) Marie-Helene Lizee, Rémy Bonardo, Jean-François Mauffrey, Thierry Tatoni, Magali Deschamps-Cottin. Relative importance of habitat and landscape scales on butterfly communities of urbanizing areas. Comptes Rendus Biologies, 2011. ⟨hal-02109128⟩
(4) Lizée, MH., Manel, S., Mauffrey, JF. et al. Matrix configuration and patch isolation influences override the species–area relationship for urban butterfly communities. Landscape Ecol 27, 159–169 (2012). https://doi.org/10.1007/s10980-011-9651-x
(5) Deschamps-Cottin, M., Barthélémy, C., Bertaudière-Montès, V., Blight, O., Bossu, A., Consalès, J. N., ... & Marco, A. (2013). Urban natures in Marseille: what possibilities for a green framework?. Urban green frameworks. From scientific research to urban project.
(6) Urban, M.C., Alberti, M., De Meester, L. et al. Interactions between climate change and urbanization will shape the future of biodiversity. Nat. Clim. Chang. 14, 436–447 (2024). https://doi.org/10.1038/s41558-024-01996-2