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Ville et biodiversité

The return of the Wild

For most people, the word ‘biodiversity’ tends to conjure up images of luxuriant tropical rainforest rather than plants growing around the trees on an urban boulevard. And yet the ecosystems now emerging in the hearts of cities are arousing increasing interest both from the general public and from scientists.
It was towards the end of the nineteenth century, under the French Second Empire, that Nature was officially introduced into public places in Paris. However, it was a highly domesticated Nature. Under the direction of Jean-Charles Alphand, director of public highways and roads in Paris, and Baron Haussman’s right-hand man, the Bois de Boulogne and the Bois de Vincennes were remodeled and the Parc Monceau transformed, while completely new parks and gardens were created from scratch, such as the Parc des Buttes-Chaumont, the Parc Montsouris, the Champ de Mars and most of Paris’s public gardens. Alphand also developed wide avenues, planted with geometrically aligned rows of trees. This neat and tidy natural environment soon became a favorite place for the elegant ladies of the bourgeoisie to stroll and show off their latest finery. For the ruling classes, it was also a way of improving law and order and public health, and of controlling society.
However, all this urban development meant that the poorest part of the population was pushed out into the fringes of the capital. A strip of land 250 meters wide, bordering the 35 kilometers of fortifications put up around Paris by King Louis-Philippe, rapidly turned into a shantytown. Just like the ‘urban jungles’ that had in earlier times taken over areas of wasteland in the center of Paris, this slum belt, the seamy side of Haussmann’s Paris, aroused the enthusiasm of a few pioneering naturalists who came to collect plants between the makeshift houses. This area was a refuge for wild biodiversity. Later, there were plans to set up a vast green belt there, but the construction of Paris’s ring road, begun in 1958, put an end to the idea.
In the thirty years that followed the Second World War, the area given over to green spaces in French cities was in constant growth, while its management became increasingly controlled. This was the great period of horticultural art and of ‘green concrete’: the lawns and thuya hedges that flourished at the time did nothing to promote biodiversity. The massive use of pesticides led to a natural environment which was no longer natural. It wasn’t until the wave of enthusiasm for ecology in the 1990s that the management of parks and gardens underwent a revolution, with the invention of ‘differentiated management’, which encourages wildlife and seeks to educate the public.
The recent history of green spaces has led to the establishment of new links between managers and scientists, as ecologists begin to discover urban biodiversity. Cities, which are home to an ever-greater share of the population, have above all become the ideal place to raise the public’s awareness of nature. What image of biodiversity do city-dwellers have, and what do they think of public policies aimed at encouraging wildlife in the urban environment? Social science researchers are busy trying to find out. In the meantime, much remains to be done to minimize the impact of cities on biodiversity, especially in the building sector.

Farming at the city’s edge

You have to feel sorry for farmers. As cities continue to encroach on their land, their job is becoming increasingly difficult, especially due to the presence of busy main roads which are difficult to use with tractors and farm machinery. And yet urban agriculture has not been recognized as ‘disadvantaged agriculture’ within the framework of the EU’s Common Agricultural Policy. “The question is not only to find out how to keep farming alive near urban centers, but also to choose the agriculture that is best adapted to this specific context,” points out Pierre Donadieu, Professor at the Versailles National School of Landscape Architecture, who in France was one of the pioneers of new thinking on the subject. “For instance, near Paris, the cereal crops of the region are almost entirely grown for export. They consume large quantities of fertilizers, pesticides and herbicides, and do little to help maintain biodiversity. Their role as an amenity for the region’s population is also limited. Organic farming, combining animal husbandry, orchards, nurseries and market gardening, and selling products locally, would be better adapted to public demand.”
To make city life and agriculture more compatible, some European urban regions have set up farming areas in which property speculation is discouraged, or at any rate strictly regulated. For instance, the South Milan Agricultural Park (Italy), set up in 1983, is equipped with cycle paths which link this rice-growing region to the city center. Farmers have started to offer services to the public, such as farmers’ markets and farmhouse catering. Near Barcelona Airport, in Spain, the Baix Llobregat Agricultural Park also aims to protect its heritage of orchards and market gardens, and make them better known to the general public. Set up in 1998, it covers an area of around 3000 hectares. It includes several hundred small farmers organized in cooperatives who sell part of their products not only in the Barcelona area but also in the rest of Spain and throughout Europe.

Surviving in the urban jungle

One of the goals of urban ecology is to understand how species colonize cities and adapt to urban ecosystems. “Cities are a fabulous laboratory for the study of biodiversity and evolution, because species are put under considerable pressure, as they come up against novel situations as to luminosity, food availability, predation, etc,” explains Philippe Clergeau, Professor at the French Muséum national d’histoire naturelle and a specialist in urban ecology. “However, this field of research is relatively recent. In France, the first research dates from around ten years ago.” Clergeau runs the ECORURB program, which was launched in 2003 for a period of ten years, and brings together ecologists, meteorologists, geographers and sociologists who are carrying out a comparative study of sites in the city centers of Angers and Rennes and the surrounding countryside. The first findings in plant ecology show that the combustion of hydrocarbons increases the nitrogen content of soil in cities. It turns out that the availability of nitrogen for plant growth is 160% greater in the city center of Rennes than in the surrounding countryside. “This gives an advantage to nitrogen-loving plants such as nettles,” Clergeau says. In addition, the air in cities contains three times fewer seeds than the air in the surrounding countryside, because walls and buildings affect air currents. Meteorological research has also shown that there is a correlation between early blossoming of cherry trees and the warmer climate found in city centers. In downtown Rennes, blossoms appear a week early.
As for animal ecology, three groups have been studied: birds, small mammals and ground beetles. “The mobility of animals is the main factor that explains their distribution in cities. Bird communities, for instance, are richer in cities than in rural environments, since their dispersion capacity enables them to take advantage of the wide range of habitats,” says Clergeau, “whereas ground beetles, which are unable to fly long distances, are less diverse in cities.” This is also the case for small mammals, which also have to deal with cats, the urban jungle’s top predators.
There are other factors that explain why some species do better than others. “Generalists, which can make use of a variety of habitats, do very well,” Clergeau explains. “Species that can adapt their behavior to the specific nature of the urban environment are also at an advantage.” This is true of kestrels: in a rural environment, these small birds of prey feed on tiny mammals, which they watch for while hovering. But in the city, they eat practically nothing other than sparrows, which they hunt by lying in wait.

Green spaces get greener

From Rennes to Strasbourg and from Lille to Marseille France), green space managers have all become converts to ‘differentiated management’. “This expression means that management varies from one site to another within the same city, and also that, overall, management is more ecological,” explains Gaëlle Aggéri, head of the Paysage, espaces verts Unit at the French Centre national de la fonction publique territoriale (CNFPT), and author of a PhD thesis on the history of differentiated management.
"The term first appeared in 1993, at a conference organized by the city of Rennes, which was a pioneer in the subject, together with Paris, Orléans and Northern European cities, which were at the forefront of ecosystem management of urban green spaces. Until then, most green spaces were managed in the same intensive, ‘horticultural’ way, which was very interventionist and chemical-intensive. However, the environmental impact of these practices was beginning to worry both the scientific community and landscape architects. On top of that, town councils wanted to cut down on the costs of upkeep. Specifically, differentiated management consists, for instance, in promoting the use of a range of local plants that are adapted to the soil and climate, in making use of wild flowers by leaving certain spaces in a ‘natural’ state, and so on," Aggéri explains. The city of Montpellier (in the South of France), for example, has created ‘dry gardens’ planted with drought-resistant species, which means that there is no need for watering. The use of pesticides and fertilizers is also being questioned. In Versailles and Strasbourg (France), the goal of ‘zero pesticides’ has been attained, and municipal gardeners weed either by hand or with a thermal device. Although there are no common standards for the moment, there is huge enthusiasm for this novel method of management. “Three quarters of the 931 annual courses on green space management provided by CNFPT concern differentiated management,” Aggéri says.

Gulls prefer the city’s bright lights

Typically associated with seaside holidays, seagulls have also become urban pests. Seagull colonies make a huge racket in the early hours of the morning, cover public benches, cars and the façades of buildings with their droppings, cause damage to roofs by ripping off bits of tarpaulin to make their nests, and during the breeding season even attack anyone who gets too close to their chicks. On top of that, even though the risk appears to be limited, they are potential carriers of diseases that can infect humans, such as salmonellosis. “The ability of the general public to put up with this nuisance depends not only of course on the bird density, but also on the urban environment,” points out Bernard Cadiou, an ornithologist at Bretagne Vivante (France). “No-one notices the populations of gulls on the Boulevard Haussmann in Paris due to the general background noise!”
Seagulls haven’t always been present in cities. “Before the 1970s, they only bred on islands. However, their numbers grew considerably due to the abundant supply of food, such as fishery waste and household refuse,” Cadiou explains. “When their natural environment became overpopulated, they set up colonies in coastal towns. They then started to fly upstream, and settled further and further inland.” In the 1980s and 1990s, the fisheries crisis and the closing of large waste dumps forced the gulls to turn to urban waste for food. “Today, island seagulls are starving, while their urban counterparts have never had it so good. In Brest (Brittany, France), seagulls have an average annual fertility of 1.5 fledglings per pair, as opposed to 0.3 for their fellows on the Molène Archipelago!” says Cadiou.
In 1993, Brest was the first city in France to organize operations to sterilize herring gull eggs, keeping the population in the city below a thousand pairs. Although these measures reduced noise levels and brought some relief to local residents, the colonies moved on after several unsuccessful attempts at breeding, which had the effect of spreading the invasion even further afield. “It’s better to act at the source by limiting the food resources to which the gulls still have easy access in the city,” Cadiou concludes.

Building with Nature

Biodiversity loss has four main causes: artificial land-use, overexploitation of natural resources, climate change, and the introduction of invasive species. The building industry plays a large role in this, due to the influence of the real-estate industry, the exploitation of raw building materials, heating and air-conditioning of buildings, and the introduction of exotic plants to embellish gardens and balconies.
For instance, the production of concrete requires the quarrying of chalk in karst landscapes, which are natural environments rich in endemic species. Sometimes the materials used originate directly from overexploited species. This is the case, for example, for certain tropical hardwood species.
Energy-positive buildings now exist, producing more heat and electricity than they consume. But what would a ‘biodiversity-positive’ building be like? First of all, it would be pollution-free, right from the stage of extracting materials, and also while it was being built. On top of that, priority would be given to locally produced materials and to materials with a label that certifies them as being biodiversity-neutral, or even positive. Such labeling already exists for wood.
On the site itself, any available spaces that could serve as a refuge for wildlife could be used, including planted walls and roofs, balconies with flowers, gardens, etc. Cities like Berlin take into account the ecological role of the plants used, as well as their impact on the urban environment. In fact, biodiversity can help to mitigate the impact of a building on the environment, via such techniques as treating a building’s wastewater by plant purification, or improving rainwater management with planted roofs.
In France, HQE (High Environmental Quality) certification makes no explicit reference to the protection of living organisms. The only reference is the first requirement, which calls for ‘harmonious relationship of the building with its immediate environment’. Less well-known in France, the British BREEAM ecological label, one of the most widely used in the world, lays down clear constraints with regard to biodiversity, and makes it mandatory to have the building assessed by an independent ecologist.
As part of the United Nation’s Sustainable Buildings and Construction Initiative (SBCI), thought is now being given to the unification of existing building certification throughout the world, on the basis of significant environmental impacts. It seems likely that the protection of species will be included. As for the phenomenon of urban sprawl and increasingly artificial land-use, the question is now in the hands of politicians and town-planners.

Roofs in full bloom

A flower bed is a lot more pleasant to look at than tarpaulin or gravel. “But planted roofs aren’t just beautiful, they also play a useful environmental role,” insists Raphaël Lamé, a director at Le Prieuré (1), a specialized French horticultural company, who is in charge of the technical commission of ADIVET (2), an association of professionals working in the sector. “First of all, they are able to store 40 to 60% of a city’s rainwater: part of it is used by the plants, while the rest evaporates.” In contrast, water running off waterproof surfaces picks up everything from heavy metals and hydrocarbons to dog feces, before entering the distribution system where it will, hopefully, be cleaned up. “Another environmental advantage lies in the fact that excess water only flows out after a certain time, thus spreading out the load on the distribution system. In this way, in the event of violent storms for instance, planted roofs can help to prevent overflows at sewage plants, which lead to pollution.” According to preliminary studies carried out by the Centre Scientifique et Technique du Bâtiment (3) in partnership with ADIVET, they also appear to have an ‘air-conditioning’ effect. During a heat wave, the temperature of the top floor in the building may fall by 1 to 3°C compared with an unplanted roof terrace. “Some builders have also measured a soundproofing effect,” Lamé adds, “with the volume of noise falling by 2 to 5 decibels.”
The plants generally used are not in the least exotic, and include Sedum, thyme, carnations, lavender, iris, etc. The roofs are subsequently colonized by wild flora and fauna. Surveys carried out in Switzerland, Germany, the UK and Canada have shown the positive impact of planted roofs on urban biodiversity. “They act as a refuge for dozens of invertebrate species,” says Tanegmart Redjala-Ounnas, an R&D engineer at Le Prieuré. “In Switzerland, birds such as the little-ringed plover, the lapwing and the skylark, whose habitat is endangered, even nest there!”

Plant architecture

The use of plants is a common theme in all architect Edouard François’s work. Fifteen years ago when he was starting out, he was commissioned to build a community of holiday homes near the village of Jupilles, in the Sarthe department (France). He made great use of plants in these dwellings, which were built at the edge of a forest, with the houses set within hedges. “The idea was not only to bring the village to the forest, but also the forest to the village,” he explains. Although François refuses to make systematic use of planted façades, several of his projects have since then used plants. The Flower Tower, which was completed in 2004, is a tower block of thirty council flats built in a local government development area in Asnières, in the Paris suburbs. All the balconies are decorated with huge flower pots planted with bamboo. “The building overlooks a park. So the idea was, yet again, to insert it into its environment,” he explains. Over and above this contextual choice, François thinks that there is a lot to be said for using plants. “Used on a façade, they create a separation with the outside world, prevent buildings from overheating, capture rainwater runoff, and absorb CO2. The Flower Tower’s bamboo also makes a soothing rustling sound, a little like a reed bed. The people who live there have told me that this sound has a very strong positive psychological impact on them.”
The next ‘plant challenge’ for François’s team is a fifty-meter-high apartment building, which will be built on the island of Nantes (France) for the Giboire group. “For this project we’re going to work with the botanist Claude Figureau, director of the Nantes botanical gardens, and with various nature conservation organizations," François says. “They’ll help us to cover the façade with plants that play a major role in encouraging biodiversity.” For now, it’s too soon to reveal more, apart from the fact that the building will look like a “giant cucumber”.

Figuring out how to make cities greener

In Paris, there are, on average, 5.8 m² of green spaces per inhabitant. If you include the Bois de Boulogne and the Bois de Vincennes, this area increases to 14.4 m². That’s far less than in Rome, with 321 m² per inhabitant, Madrid with 68 m², or Amsterdam with 36 m². In the past few years, redevelopment of industrial and railway sites has enabled the Paris town council to create the André Citroën and Bercy parks.
But how can you further increase the area given over to green spaces in this very old, compact city, where there is little spare land available? When the Paris city council reviewed the Local Planning Program (PLU) after consulting with residents, they decided to do away with the possibility of allowing all open spaces around new constructions to be developed on a concrete base. 20% of these open spaces will now have to be based directly in the soil. In addition, a percentage of additional planted space will be calculated, depending on the lack of green spaces in the neighborhood and on the treatment (fully earthen floor, earth on a concrete floor, planted roof, planted balconies, etc). “This ‘planting coefficient’ or ‘biotope coefficient’ should be at least 10% for those neighborhoods least lacking in green spaces (15% for those with the greatest shortage), for planting of land, preferably directly in the soil,” explains Mehand Meziani, an architect and town-planner at the Atelier parisien d’urbanisme (1), which carried out Paris’s PLU assessment.
"If an earthen floor is technically unfeasible,” he adds, “the builder will need to compensate by developing, for concrete bases, twice the planned planted ground area, three times the area as a roof, or five times the area as a planted wall. The builder will of course be able to combine these various approaches.” Inspired by experimental approaches in Berlin and other Northern European cities, this initiative is likely to be taken up in France, particularly by the city of Lyon, as part of its new PLU, which is now under review.

Biosourced materials aren't necessarily green

From yak wool yurts and mud huts to the most modern constructions, materials of natural origin have always found a use in building.   And now, with increasing awareness of ecological issues, such materials are being used even more. They play a role in the structure, cladding and above all insulation of buildings. As well as conventional biosourced insulating materials such as cork and wood fibers, many other materials have recently made a breakthrough, such as those based on hemp, cotton or flax fibers, straw, duck feathers, sheep's wool, etc. Recently, we've even seen insulating materials based on algae and oyster shells! Some of these biosourced materials are treated in order to prevent the occurrence of mites, clothes-moths or fungi. This is why it's important to verify not only their technical performance but also their inoffensiveness to future occupants (1). As for their added value, this theoretically concerns the 'grey energy' that is saved by using such materials, in other words all the energy required to produce them and transport them to the construction site. However, with regard to its energy budget, a panel that has traveled several thousand kilometers before being installed may not be quite so green after all, even if it is made of cork!

1 – See the French reference data base on the environmental and health performance of building materials (INIES)

Redesigning cities

Today, urban green spaces are no longer created for purely aesthetic or health reasons. Henceforth, the goal is to protect biodiversity, which is under threat from the expansion of built-up areas that break up natural habitats. For there is great cause for concern: in Europe, the area per capita given over to cities has more than doubled in the past fifty years. For instance, the last two decades have seen an approximately 20% increase in the area of towns in many countries in both western and eastern Europe, whereas the population has risen by a mere 6% over the same period.
We now face a twofold challenge. We need to increase the area given over to natural habitats in cities so as to promote the free movement of species, while at the same time maintaining a dense urban fabric in order to avoid sprawl, which is harmful to biodiversity. Previously considered simply as a factor involved in the destruction of nature, cities are in the process of becoming key players in the protection of biodiversity at both regional and national levels.
The green and blue networks currently being set up link natural habitats together, enabling animals and plants to move along ecological corridors connected to the city's surroundings. By including footpaths and cycle paths, this kind of green grid is also of benefit to city-dwellers, who increasingly seek natural surroundings.
Some cities are already putting this concept into practice. For instance, Nantes is making use of the many waterways that criss-cross the city. Brussels has plans for a green grid that will link up the Belgian capital's parks, while Barcelona is aiming to set up a green corridor in the city center.
Elsewhere we are seeing the emergence of eco-friendly developments, such as the well-known BedZED in the UK, the Vauban district in Germany and the Eden Bio development in Paris. These high environmental quality neighborhoods are designed according to the principles of sustainable development. Renewable energy, energy efficiency, increased use of public transport, local facilities, footpaths and cycle paths are just some of the solutions employed with the aim of reducing the ecological footprint and impact on biodiversity. And architects have plenty of ideas up their sleeves, such as vertical eco-friendly neighborhoods in the form of towers equipped with farms, buildings that clean up pollution, floating cities, and a whole host of other futuristic projects.
However, while waiting for these ideas to become reality, rational development of biodiversity in cities will already be providing essential ecological services to city-dwellers, such as flood prevention, and air, water and waste treatment.

How to design an ecodistrict

Although ecodistricts are frequently presented as being the definitive solution for sustainable cities, there is no clear definition of what they are."The word appeared as a result of a wider public becoming aware of a number of existing pioneering projects," explains Taoufik Souami, a senior lecturer at the French Institute of Urban Planning who has written a book on the subject (1). Such projects, which emerged in Northern Europe in the 1990s, took into account energy, waste, transport and water resources, but hardly ever biodiversity."To the best of my knowledge, only two out of a total of at least ten projects included measures to protect biodiversity:Vikky, in Helsinki, Finland, and the Kronsberg district in Hanover, Germany.In both cases, construction was preceded by an impact assessment on habitats and species, and compensatory measures were applied," Souami goes on.
In the last twenty years, ecodistricts have started to take off, especially in France, where the Government has recently begun to take an interest in the issue.The first law to emerge from the Grenelle Environment Forum makes it mandatory for towns that have "a significant habitat development program" to create an ecodistrict by 2012.In order to spot the most promising projects and establish a frame of reference, the French Ministry of the Environment (2) launched an annual competition in 2008.
The Le Raquet district (3), between Douai and Sin le Noble in the Nord department, was one of three prizewinning projects in the 'Biodiversity' category in the latest contest.  "It was designed to fit into the ecological connection between two protected natural areas:  the Scarpe-Escaut regional park to the north, and the Censée valley to the south," explains Florent Chappel, project manager at the Urban, Habitat and Landscape Planning Department at the Ministry of the Environment. "To do this, around fifty hectares of green spaces will be developed there, divided into five parks maintained using differentiated management." One of them will be given over to sports activities, another will be an area of forest and play a role in protecting wetlands, producing energy from biomass conversion, while a horticultural park will include several plots reserved for organic market gardening. Before building begins, a species inventory is planned with a view to monitoring biodiversity. The district will also host an environmental education center.  And lastly, the project will place special emphasis on the treatment of rainwater, which will be carried out on site using constructed wetlands. The project began in 2008, and should be finished around 2015.

1 - Ecoquartiers, secrets de fabrication, by Taoufik Souami. Editions les Carnets de l’Info, collection  "Modes de villes".
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3 - To find out more about the Le Raquet project:

Green-blue networks for cities

In France, the recent Grenelle Environment Forum made the creation of urban green networks one of its top priorities.  The goal is to protect against the loss of biodiversity caused by the expansion of built-up areas that break up natural habitats. The idea is to link natural habitats together, enabling animals and plants to move along ecological corridors connected to the city's surroundings. Green grids of this kind can be based on existing links, such as tree-lined avenues, railway lines, embankments, vacant lots, wasteland, etc. Cyclists and walkers can also benefit if footpaths and cycle paths are included. Blue networks, consisting of planted watercourses and bodies of water, could complete the network.

But how can such networks be made effective, so that the various species present in cities actually make use of them? What type of vegetation should be planted? What about the impact of lighting and noise? What ecological services could they provide? Is there a risk that they will promote the presence of species that are undesirable or that carry diseases transmissible to humans? How can such networks fit into city planning programs?  To such questions scientists still have very few answers. Hence the importance of the French 'Urban Green Network' research program1 launched in 2009 and involving eleven research groups in the life sciences and social sciences in seven cities. Results are expected in 2012.

However, several cities throughout the world have already begun to apply the concept. For instance, Nantes is making use of the many waterways that criss-cross the city. Brussels has plans for a green grid that will link up the Belgian capital's parks. In Curitiba, Brazil, an ecological corridor dubbed 'green line' will connect neighborhoods which until now were separated by a highway. And Barcelona is aiming to set up a green corridor in the city center.

1. Program funded by the French National Research Agency with the participation of CNRS.

Some myths about urban density

To put an end to the urban sprawl which gobbles up natural habitats and farmland, to the development of single-family detached housing which requires huge amounts of space, and to the increased road traffic that this generates, there's only one solution: densifying cities. "However, this idea is not popular with the general public," explains Eric Charmes, a senior lecturer at the French Institute of Urban Planning.

People may have a mistaken view of the density of a neighborhood (1). In fact, contrary to popular belief, high-rise apartment buildings in suburban housing estates, surrounded by vast open spaces, are no denser than the center of a village. And both these types of housing are four times less dense than a block of Haussmann buildings in the center of Paris. "In fact, Paris is one of the densest cities in the world," Charmes says. "With the exception of some cities in India or China, the only other comparable city is New York. So density isn't synonymous with social distress. In Paris, those who can afford it pay a great deal for the right to live in an extremely dense environment. It's the attraction of city centers, where there are services, cultural facilities, public transport and so on, which explains why density is not only accepted but sought out. People obviously don't want to live in crowded areas if they aren't attractive!"  
However, there are some reservations about the positive effect of urban density on the environment. Jean-Pierre Orfeuil, a professor at the Paris Institute of Urban Planning, points to the 'barbecue effect' or 'compensatory mobility', which drives people who live in city-centers out of town at weekends.  "With the same income, they are more likely than those living on the outskirts to travel long distances, using energy-hungry means of transport such as planes. Indeed, a Norwegian study suggests that an intermediate type of housing, such as dense residential suburbs, might be the best compromise," Charmes concludes. 

1 – The ratio of the number of square meters of living space to the total area of a neighborhood.

Imagining the green cities of the future

Lilypad, a half-submerged floating city inspired by the waterlily, which would accommodate climate refugees; Dragonfly, a 600-meter-high tower in the heart of Manhattan that would be home to offices, apartments and farms; and Anti-Smog, a building that would help to reduce air pollution, set in the heart of Paris. The Belgian architect Vincent Callebaut and his virtual architect's office, Vincent Callebaut Architectures (1), which he set up with ten young colleagues from all over the world, are busy imagining the cities of the future.    A city that has no choice but to be green. "Rather than just accepting the ecological disruption of the planet, we have chosen to provide some solutions," explains Callebaut, who describes himself as an 'experimental architect'.  To do this, he is proposing a radically novel vision that runs counter to contemporary architecture, which in his opinion is too inert and fails to question our current way of life.  According to Callebaut, tomorrow's towers will be genuine urban neighborhoods, bringing together different social classes and activities.Such vertical eco-neighborhoods will provide their own energy from a battery of solar panels and high-tech wind turbines. "In addition," Callebaut explains, "our buildings are designed in such a way that nature will take them over.  Lilypad, for instance, would be surrounded by aquaculture units, which would act as niches for wild species."  By densifying cities, such 'islands of Nature' would free up space for biodiversity in their immediate surroundings. 

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Biodiversity, the city’s ally

By 2050, it is expected that there will be a deterioration in most of the services provided to humans by ecosystems. One of the main reasons for this situation is rampant urban development. And yet, city-dwellers benefit from nature in very concrete ways. Agriculture, water treatment and green spaces for recreation are just some of the everyday examples of the ecological services provided by biodiversity.
For instance, certain ‘sentinel’ species serve as indicators of environmental quality. In the nineteen seventies, correlations were established between the intensity of sulfur dioxide pollution and the number of species present in lichen populations. Honeybees are another iconic species. In towns, they pollinate plants, and usually produce more honey than in the countryside, two services that are by no means insignificant. However they also provide another, less well-known service: analysis of the honey or pollen shows whether the environment where it was gathered is contaminated by various pollutants, such as polycyclic aromatic hydrocarbons.
But that’s not all biodiversity does for us: it also treats the air, water and waste of our cities. In the late nineties, New York decided to invest massively in the restoration of wetlands which naturally purify the Big Apple’s water supply. In France, plants are being tested in wetlands downstream from sewage plants to eliminate several pollutants such as pesticides and drug residues. And some species even provide services in your own home. For instance, earthworms transform household waste into compost. And they’re now being tested to see if they can break down organic matter present in urban wastewater. And certain conifers can improve air quality by capturing harmful fine particles from car exhaust, while noise pollution can be reduced by growing noise-abatement plant barriers.
And biodiversity can provide city-dwellers with many other services. Some studies show that increasing planted surface area can significantly reduce the urban heat island effect. Natural areas, or areas that have been restored to a natural state, can also limit damage caused by flooding. For instance, the Bois de Boulogne and the André Citroën park in Paris could be used to store overflow from the River Seine. And upstream from the capital, wetlands directly protect Paris by helping to regulate water flow. Vegetation also reduces erosion phenomena and risks of landslip. And finally, according to some estimates, 800 million people all over the world depend on urban and peri-urban agriculture.
More generally, biodiversity contributes to the general public’s health and well-being. Parks and public gardens are not only beautiful, peaceful places, but also venues where the public can meet, exchange and learn.

Bees as environmental sentinels in France

Of course, one of the chief services provided by bees is pollination. However, certain species can also be used as indicators of plant diversity in towns, and of contamination of the urban environment by certain pollutants. This can be done by studying colonies and carrying out analyses of collected pollen, honey, nectar, beeswax and dead bees.
But doing this requires the development of an effective and fast-reacting system. This was one of the aims of a study recently carried out by the Evolution, génome et spéciation Laboratory (LEGS1). Gérard Arnold’s team has managed to develop a strict protocol which could well serve as a benchmark for this kind of work. This consists in equipping hives with electronic sensors that continuously count the number of bees flying in and out, as well as with an automatic balance that weighs the hive several times a day. The data is stored in a laptop and can be sent daily by SMS. “As soon as an anomaly is detected, we can rapidly go to the site to check the state of the colony, and take samples for sanitary and toxicological analysis,” Arnold explains. “We need to be able to react quickly, especially when it comes to analyzing pesticides, which can break down in a short time.”
The LEGS team tested the system successfully for three years on nine domestic apiaries in the Paris area with bees of the species Apis mellifera: three in an urban area, Saint-Denis (Seine-Saint-Denis), three in Rambouillet (Yvelines) and three in Saint-Cyr-sous-Dourdan (Essonne). “Unlike the other two sites, we didn’t record any loss of colonies in Saint-Denis,” Arnold says. “In addition, the urban bees had no specific problems, and produced more honey than the bees located in the rural areas of Rambouillet and Saint-Cyr-sous-Dourdan.” This is the first time that a scientific study has backed up the many observations that show that the activity of bee colonies is excellent in an urban environment.
However, Arnold is also a member of the steering committee for an ongoing large-scale study in the Pays de la Loire region*. The main goal of the study is to use Apis mellifera as an environmental sentinel for pollution by lead, pesticides and polycyclic aromatic hydrocarbons. “In all, 144 samples have been taken from 16 apiaries throughout the region, four of which are in an urban environment in the heart of Nantes,” explains Monique L’Hostis, the researcher who is leading the project. “Analyses are currently being carried out on honey, pollen, beeswax and bees’ bodies.” Specific multiresidue analytical methods for around 80 different pesticides are being used, which were developed by CNRS’s central analytical department at Solaize2 (Rhône). All the results will be correlated with those from field surveys (spraying with pesticides, discharge of pollutants, vegetation cover, etc). Conclusions are expected at the end of 2010.

Earthworms to purify your water

In 2004, the town of Combaillaux in the Hérault department (France) equipped itself with a new kind of water treatment plant. What’s unusual about the plant is that it makes use of the ability of two species of earthworm, Eisenia andrei and E. fetida, to break down organic waste present in wastewater by ingesting it. The big advantage of this biological treatment is that it doesn’t generate the foul-smelling sewage sludge that saturates incinerators and landfills, and that some farmers refuse to spread on their land. The technique also produces less final waste. And on top of that, the process uses less electricity and doesn’t need much room.
In practice, the worms act on two levels. Some of them are used for the treatment of solid waste with a size exceeding 2 mm, recovered after screening wastewater at the plant input. In less than three months, 80% of the waste is turned into vermicompost, which is humus that can be used as a natural fertilizer. The other worms operate on the residual liquid after an aeration stage needed to ensure the efficacy of the system. Around 2 500 000 Eisenia work together with bacteria in a tank roughly 100 m² in area containing pine bark, wood shavings and pebbles, and break down the remaining organic matter. In this way, every square meter of the ‘vermifilter’ can treat the wastewater produced by two to four people.
“The water recovered from the vermifilter complies with all the health standards in force, except with regard to phosphorus,” explains Patricio Soto, a research engineer at INRA1 and the manager of LombriTek Eco-innovation, the company which performs the technical monitoring of the Combaillaux plant. “After chalking up this first success, we should soon be equipping two more towns in the Ain and Morbihan departments (France), but this time using second generation worm-based sewage plants.” The plants will be equipped with even finer screening facilities, a better-adapted tank, and a specific complementary treatment for phosphorus. All this without either the conventional bacteria bed or combined decanter-digester, which produce sludge. The only limitation is that such plants are only suitable for towns with no industrial activity likely to cause peaks in toxicity due to mercury, copper or arsenic. This is because the earthworms die if they ingest water contaminated with this type of pollutant.
However, we haven’t heard the last of Eisenia. They are already being used by some individuals, companies and local authorities to turn organic waste into compost2 on the spot. And in the future, they might even be used to treat water directly in our homes. With this in view, Soto’s company is taking part in the Napevomo project3. The goal is to build a life-size modular positive-energy house equipped with a vermifilter.

The Dragonfly zone

Since August 2009, an additional innovative system has been helping to treat wastewater from the water treatment plant at Saint-Just in the Hérault department (France). Dubbed the ‘Zone Libellule’ (‘libellule’ is the French word for dragonfly, and an acronym for ‘LIberté Biologique Et de LUtte contre les poLluants Emergents’—Biological freedom and fight against emerging pollutants), it is made up of a series of wetlands containing over 7000 plants from 48 different species. These local plants have been chosen for their ability, demonstrated in the laboratory, to rid water of some emerging pollutants present in trace amounts and which are subject to European regulations, such as pesticides, drug residues, metals, etc.
For instance, there’s water-mint, which can absorb zinc, compounds of which are found in many cosmetics, and reeds, which are able to eliminate some pesticides. “Plants and trees interacting with bacteria, varying flow rates and depths, a residence time for water of around ten days, the action of sunshine, etc: it’s the combination of the various factors in this ecosystem, which is one and a half hectares in area and rich in biodiversity, that is expected to make it an effective purifier, and it doesn’t need any specific maintenance either,” explains Eric Blin, who’s in charge of this project managed by SDEI, a subsidiary of the Lyonnaise des Eaux (a French firm). The Zone is overseen by a scientific committee that includes Christian Drakidès, an ecologist at the Hydrosciences laboratory1 in Montpellier. “During the three years that we’ll be monitoring it, we’ll be using our expertise to study and model the treatment of water by plants and microalgae,” Drakidès adds.

Purifying and cooling the air

A certain number of plants, especially conifers, are able to capture the harmful fine particles emitted in car exhaust. However, for maximum efficacy in towns, where should they be planted, and in what form? Researchers from the Image, Ville, Environnement Laboratory1 in Strasbourg (France) are trying to find the answer by using numerical simulations. “In narrow streets lined with high buildings, our work shows for instance that hedges capture more particles at chest height than a line of trees,” explains Christiane Weber, senior researcher at LIVE. “According to our model, the crowns of the trees tend to block air circulation, which concentrates the particles at ground level.”
Plants can also cool down air by evapotranspiration. As part of the Descartes group for the study of the ‘Greater Paris’ project, the Groupe d’étude de l’atmosphère météorologique 2 (GAME) simulated the impact in 2030 of a 30% increase in woodland in the Paris Region, the replacement of cereals by market gardening in a 50 km radius round Paris, and the creation of extensive reservoirs. “According to our results, this scenario could bring down nighttime temperatures in central Paris by as much as 2 °C during heat waves,” explains Valéry Masson, a researcher at GAME. “This is an encouraging avenue of research, since the persistence of high temperatures at night plays a decisive role in the excess mortality observed during heat waves.”

Well-being and health

More and more scientific studies are showing that biodiversity improves moral and physical well-being. For instance, two epidemiological studies carried out in the Netherlands show that the residents of neighborhoods with abundant green spaces state that they have fewer health problems. And in Japan, two other studies also show that people who make use of urban green spaces live longer.
The current success of urban gardens backs up these scientific findings. The success of community gardens in Canada and the US has led to a profusion of initiatives in France, where novel kinds of community garden have developed since the beginning of the 1990s. Mainly targeting the inhabitants of dense urban neighborhoods, community gardens foster social bonds, neighborhood solidarity and conviviality. Social integration gardens, on the other hand, are often located in outlying districts. They promote the integration of people in situations of social exclusion, or those who are in social or professional difficulty.
The restoration and regeneration of urban rivers also have extremely positive effects on city-dwellers. The Cheonggyecheon river in Seoul is a fine example of this. The river, which had been completely buried beneath highway infrastructure, was entirely rehabilitated over a distance of more than 5 kilometers shortly after 2000. In addition to providing enjoyment for the 50,000 people who walk along the newly planted riverbanks every day, the project has noticeably reduced the local urban heat island effect, air pollution and ambient noise levels.
However, this new enthusiasm for Nature shouldn't let us forget that a number of species present in the urban environment can be harmful to human health. For example, this is the case not only for pigeons but also for mice and rats, which can transmit diseases to humans. At the same time some plants can cause allergic reactions, especially in cities, where air pollution makes the body more vulnerable.
In conclusion, biodiversity can render many services to city-dwellers, and its protection is a crucial challenge for our urban societies. However, it is necessary to develop it in a rational and efficient way. What is the best way of reconciling Nature, human activity and urban density? How can towns be designed so as to avoid disturbing the animals and plants who live there? Which species should be introduced or encouraged? How can they be enabled to move around? These are all questions being tackled today by scientists working in multidisciplinary groups. Green and blue grids, ecological corridors, eco-friendly neighborhoods, vegetated buildings, farm parks, regenerated watercourses, gardens, vertical farms: there's no shortage of ideas being explored. In the end, there is probably no such thing as the ideal town, but rather a profusion of solutions to be tried out and adapted to the context of each individual city.

Rebirth of a river in Seoul (Republic of Korea)

In spring 2003, the Mayor of Seoul gave the go-ahead for a Herculean project: the restoration of the Cheonggyecheon stream, which had been completely buried beneath highway infrastructure in the heart of the South Korean capital for over 25 years (1). The figures for this undertaking are mind-boggling: 700,000 workers were mobilized, around 7,200 information meetings organized, over two million plants put in, 21 bridges built, and a linear distance of 5.84 km restored, all for a budget of around €248 million. On 1 October 2005, two years and three months after the work began, the public got their first view of the newly-restored Cheonggyecheon. Today, an average of 50,000 visitors stroll along its banks every day. Besides the technical achievement, what are the benefits to the population? According to the figures of the public authorities, the results are very satisfactory in this respect as well. Under the combined effect of the water and of the wind generated by the area’s new layout, the temperature at the river site has gone from 2.2 °C warmer than other parts of the city to 0.9 °C cooler. As for air pollution, the concentration of airborne particles has fallen by 15.3%, that of nitrogen dioxide (NO2) by 25.3% and that of BTEX (2) by 25-62%. Ambient noise levels by the waterside have fallen from 73.8 to 62 dB (A) during the day. And, last but not least, biodiversity has become considerably richer. According to surveys carried out, the number of species living in the area has risen from 98 in 2003 to 788 in 2009. Today, no less than 471 plant species, 245 insect species, 34 species of bird, 27 fish species, 7 species of reptile and amphibian, and 4 species of mammal can be found there. There are even some protected species living on the site, such as the Korean salamander. Elsewhere in the world, many other urban watercourses are also being restored.

Urban community gardens

Community gardens in urban areas are nothing new. They first appeared in the 1970s in the US and Canada. In New York there are now around 600 such gardens. Their success led to a profusion of initiatives in France, where novel kinds of community garden have developed since the beginning of the 1990s. They are also the successors of nineteenth-century allotment gardens for workers ('jardins ouvriers'), which were subsequently redubbed 'family gardens'. Today, they are usually grouped in two categories: shared community gardens and social integration gardens.

Mostly located in city centers or inner suburbs, the main purpose of community gardens is to foster social bonds, solidarity and conviviality within a neighborhood. They are open to passers-by, are not split up into individual plots, and are frequented by people of all ages and ethnic groups who undertake environmentally-friendly gardening. Flowers, fruit and vegetables are grown, although not as a serious source of food due to the small surface area of such gardens.  Created, developed, looked after and run by groups of local people who belong to neighborhood associations, community gardens are also a setting for recreational, festive, educational, cultural and artistic events. They are flourishing in all of France's major cities, including Paris, Lyon, Lille, Nantes, Marseille, Bordeaux and Brest.

Social integration gardens, which require more land, are often located in outlying districts. Their purpose is to use gardening as a means of rehabilitating people who are in social or professional difficulty,  such as the unemployed, people living on benefits, the disabled, the lonely, young people with learning difficulties, and former prisoners.  They all work under the guidance of voluntary or paid helpers.   These gardens were invented at the end of the 1980s as a response to rising unemployment and poverty. Fruit and vegetables are mainly grown for food, either for the grower's own use, or to be sold or given away. In France there are estimated to be several thousand users grouped together in associations.

The hidden face of biodiversity

Biodiversity has many benefits for city-dwellers. Nonetheless, a number of species present in the urban environment can be harmful to human health, as we’ve been reminded recently by two examples that received huge media coverage: the avian flu virus, transmitted by birds, and the chikungunya virus, carried by mosquitoes of the genus Aedes.
But apart from these well-publicized cases, many other animals in cities are disease carriers. Pigeons, for instance, can transmit certain microbes to humans, which can cause diseases such as salmonellosis, chlamydiosis, toxoplasmosis, ornithosis, or even acute fungus diseases such as cryptococcosis. This problem is being investigated by several scientists involved in the research program ‘Urban pigeons: reconciliation ecology’, in which the Ecologie, systématique et évolution Laboratory1 is taking part. In addition, their nesting sites can swarm with parasites such as ticks, mites, bugs and fleas, causing allergic reactions. According to the World Health Organization, direct infection of people through contact with urban birds or their habitats has been recorded for seven different diseases.
Still, birds aren’t the only ones to blame. For instance, several studies have shown a clear relationship between growing domestic exposure to allergens carried by cockroaches, mice and mites, and an increased risk of severe asthma. Of even greater concern is the fact that the fleas of some rodents can transmit murine typhus. Because they can be infected by a wide range of parasites and pathogens, rats (Rattus norvegicus, Rattus rattus) and mice (Mus musculus) are also a threat to people in poor health.
As for novel household pets, which are becoming increasingly fashionable, they can carry viral, bacterial or parasitic zoonoses. For example, plague can be transmitted by certain wild rodents, salmonellosis by reptiles, tuberculosis by some birds, herpesvirosis B by Asian macaques, rabies by other primates, etc.
Turning to plants, the pollen of ragweed, various grasses, cypress, birch, etc can cause allergic reactions such as rhinitis, conjunctivitis and asthma. This is a health problem that mainly affects the more sensitive city-dwellers rather than country people, whose immune system is boosted by direct contact with the rural environment. On top of this, pollution makes people more sensitive to allergies and also stresses plants, which pollinate even more as a result.
Over the next few decades, it is unfortunately probable that climate change will lead to the emergence of new infectious and parasitic diseases, due to the introduction of disease-carrying tropical species into France.

How to fight stress naturally

Does the presence of nature in the urban environment have an effect on the health of the public? This is a question that scientists have been investigating for several years.
One of the pioneering studies in this field was published in 1984 in the highly prestigious journal Science. The US researcher Roger Ulrich showed that patients who had undergone gallbladder surgery recovered more quickly when they were in a hospital ward with a view of a natural landscape than if they could only see a brick wall. The former needed fewer painkillers than the latter, and on average were able to leave hospital a day earlier.
Since then, there has been a buildup of scientific evidence about the positive relationship between well-being, health and green spaces. In his book ‘Une écologie du bonheur’ (‘The Ecology of Happiness’), Eric Lambin, a professor of human-environment interactions at Louvain Catholic University (Belgium) and Stanford University (United States), shows that, according to some studies, being close to or even just being able to see nature increases well-being in the workplace. For instance, people with a sedentary job who have a window with a view of a car park, a street or buildings suffer more frequently from headaches than those whose window gives onto trees, shrubs and flowers. Other work shows that the residents of dilapidated neighborhoods that are without natural vegetation appear more often to show symptoms of chronic stress and suffer from health problems.
In contrast, two epidemiological studies carried out in the Netherlands show that the residents of neighborhoods with abundant green spaces state that they have fewer health problems. In Japan, two other studies also show that people who make use of urban green spaces live longer. And finally, many studies show that contact with nature is an effective way of recovering from the mental fatigue caused by the ever-faster pace of modern life.

CNRS    sagascience