Urban biodiversity: seven questions for Isabelle Spiegel and Philippe Clergeau

Isabelle Spiegel is the head of VINCI Environment Department. She is tasked with implementing the group’s environmental missions. Philippe Clergeau is a professor at France’s National Natural History Museum in Paris. He leads a team of researchers in urban biodiversity and is working on introducing biodiversity in cities. In 2020, he published Urbanisme et biodiversité with Apogée publishing. Both consider urban biodiversity to be a major topic that needs to be addressed. They share their opinions with us.

How does biodiversity manifest itself in cities?

Philippe Clergeau : Are we talking about nature or about biodiversity? Because the difference is important. Nowadays, we’re pretty good at allowing nature in the city – we’re planting flowers, we’re more horticultural. When we’re talking about biodiversity, we’re talking about a different relationship between the plant, animal and human species: we’re talking about ecosystems. This has often made me write that sustainable cities could not exist without integrating the urban ecosystem into a regional ecosystem, developing a true biodiversity based on local native species. Up until recently, we did everything we could so that zero species could make the city their home. We would use pesticides and systematically clean the pavements…. We would choose plants for their aesthetic quality, and we would tolerate a few animal species such as ducks and small birds. Since the Grenelle de l’environment measures, preventing the use of pesticides in cities has had a major impact towards change. It has enabled small flowers – or “weeds” – to grow, we’re now seeing more insects, more insect predators etc.… Food chains are appearing.


Isabelle Spiegel : In the collective unconscious, we associate urban biodiversity with rooftop beehives, which is a little careless. While the role of pollinators is essential, it’s far from enough. We need to recreate complete habitats in urban spaces, habitats that are going to welcome plant and animal species. I’m thinking of wildlife corridors: it’s about providing places for animals to stay. I’m thinking of migrating birds who must be able to cross a megalopolis by finding a pond or habitats that correspond to their migratory needs.


Why is biodiversity such an important topic?

PC : The challenges linked to nature in cities have been well seen around what we call ecosystem services. This is basically the services gifted to city-dwellers by the natural environment, such as pollution and flooding regulation. There is also a huge cultural issue. We need vegetation in cities, like walking on grass or in amongst the trees. We mustn’t forget about food production services; urban farming is developing even if it still remains on the fringe. And finally, today the most progressive concerns health services: all these regulations which provides city-dwellers with comfort and well-being, such as against urban heat islands.


IS : I remember two striking figures. The first concerns species extinction, which is 100 to 1,000 times faster today than the natural extinction rate. The other concerns demography: 2.5 billion extra people will live in cities from now until 2050. This is the equivalent of 65 new megalopolises the size of Tokyo. If conquering new space means rendering it artificial, we are going to put incredible pressure on a biodiversity which regulates the carbon cycle, water cycle and photosynthesis. The services provided by nature go way beyond the simple food chain. For example, sponge cities are going to absorb a part of water surplus during floods, and raise the question of creating voluntary flood-risk areas.


How can we enhance biodiversity?

PC : By using on ecological engineering. With my team, we work a lot on wildlife corridors which encourage a varied biodiversity to make their home. We’re also working on buildings. Today, 90% of green rooftops are covered with sedum, a small waxy plant that only needs a substrate layer depth of two to three centimetres. We have shown that animal biodiversity does not come in these conditions, hardly either for plant biodiversity too. Ecological engineering has been beneficial in encouraging deeper substrate layers for encouraging grass or even small bushes to take root, and insects to make their home.


IS : Another challenge today is knowing how to evaluate the benefits of biodiversity. There is no simple way to measure it. The European Commission has recently published a list which features 80 different evaluation methods. Putting in place these devices is fundamental for reaching out to decision-makers, and for integrating elements of ecosystem enhancers in all areas of projects. I think one of the priorities should be to think on a neighbourhood level and not only having a simple building or a park, but having an integrated approach. These days we know how to create positive results on an industrial wasteland that is poor in biodiversity. But they remain difficult to show. They range from average indicators, such as eliminating phytosanitary products. Biodiversity is still considered as secondary in terms of environmental assessment in its methodology.


What is stopping biodiversity from developing in cities?

PC : There is no such culture amongst designers. Urban design is far from integrating environmental concerns, even if there are winds of change in the wake of huge public demand. The majority of cities are aware of the importance of developing something other than pretty floral displays, and this is acknowledged a little throughout. Cities are also aware that certain overly invasive species should be limited, and native species should be prioritised. But to take things further and modify our urban design, we need to reach out to urban planners, decision-makers, developers… When cities manage to bring about change, it’s often thanks to a mayor or deputy mayor’s strong, passionate drive.


IS : I’ve already talked about indicators: we must all agree on the objectives. This leads us directly to the question of expertise. We need ecologists, but specialists in the field are few and far between. You need to find the right balance between cutting-edge knowledge and teaching the minimum of skills in everyday operations. Property developers and project managers must develop an understanding of the issues surrounding biodiversity in order to anticipate them in the design phase. Cities’ markets have been very fragmented for more than 50 years now. As soon as we approach the subject of biodiversity, we must redraw the boundaries between different stakeholders, in an area that is still poorly regulated. If you want to be ahead of the curve in terms of regulation, you’re quickly faced with governance issues.


What are the financial arguments for developing natural environments in the city?

PC : The issue of price comes up time and again, and indeed, changing current practices carries additional costs. But if we look at things in the mid-term, it’s a winning situation. It’s easier to blast the pavements clean with a pressure washer than it is cutting grass. But when faced with heat waves and flooding, it’s grassy, plant-based surfaces which are going to help regulate this. There’s always three to five – even eight – degrees difference in temperature on a green, plant-filled street compared to the same street without trees.


IS : It’s not easy to find the right business model. We receive all the natural services provided by biodiversity, such as pollinating bees, but we don’t know how to put a cost on them. The value created is important but not necessarily immediate…


Should we then re-think the idea of what a city is and how it is designed today?

PC : I absolutely don’t have the vision of the ideal city. Strategies aren’t valid throughout. We’ve more or less got the main ideas: we know we must create green corridors so people can go for a walk, and we must limit the number of vehicles – be they electric powered or not. Today I’m working on the the aim of “artificialisation neutrality”: how can we ensure that the city stops spreading out further, without over-populating. I’m also the scientific director of a plan for the Ministry for the Ecological and Inclusive Transition. We’ve just launched a Biodiversité, Aménagement Urbain et Morphologie tender which shall finance urban projects.


IS : I think that it’s important to consider the city in its whole, district by district, and think of the different services the city must provide. It’s no longer conceivable to live in the west of the city and work in the east, or take a weekend break on Sunday in search of fresh air and get stuck in traffic for two hours. We need to reconcile the different uses and consider the city as an ecosystem which responds to accommodation, food, shopping and work needs. It’s a systematic approach. Even if we consider the city vertically with its towering skyscrapers, we need to think about how to introduce nature, to keep a much needed balance.


Anything else to add? 

PC : We must aim for a living landscape, not just an aesthetical one: this is the new major paradigm. It’s not enough to think that a bit of green street furniture and plants are going to solve our problems. Working on the open ground is essential, it’s a fundamental issue for preserving a city that is not completely made out of concrete, one that can survive the heat, the floods and pandemics. Here’s a good example: the more species we have, the greater our capacity for filtering out germs. An overly abundant species like humans is a breeding ground for developing viruses.


IS : The topic isn’t new, but it is currently gaining momentum. There is a growing interest from operators, building owners and even the construction industry, which is relatively recent. There is still a lot to do, but I hope that the markets will become more dynamic and structured. We have no choice but to integrate biodiversity into the urban ecosystem.

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