Greening the City

Biodiversity, the city’s ally

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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.