Why should nature exist in the city?
Because of their complexity, their heterogeneity and the constant disturbances that occur there, urban centres are not a favoured location for animal and plant species. The exceptional anthropogenic pressure (human impact on the environment) and the limitation of ecological continuities (functional connection between two ecosystems) constitute a major obstacle to the correct development of fauna and flora. Why preserve and develop the natural world within the city? What tools are available to support this development?
Urban biodiversity does not only play an aesthetic role within cities: it plays a determining role for the good environmental quality of cities and can even be considered a public health issue.
Indeed, plants contribute to good water management as green facades and roofs prevent streaming and store rainwater to then release it into the atmosphere through evapotranspiration. As a result, rainwater networks do not saturate. Similarly, non-waterproofed soils not only limit the drying out of phreatic tables but also, if presenting enough green surface, limit river flooding.
Thanks to shade and evapotranspiration that trees provide, cities’ temperatures remain cool. Shade prevents overheating of the surface and limits the urban heat island effect. Modelling carried out on July 8, 2010 at 4 p.m. in a north-south facing street in Nantes (France) established that the presence of two green facades allowed to lower perceived temperature from 0 to 3 ° C. One could even gain up to 10 degrees by planting 2 rows of evergreens. From an energy perspective, such green walls can reduce consumption by 5 to 70%! (1)
As previously mentioned, nature in the city plays a determining role when it comes to people’s health and well-being. It helps reduce stress and promotes physical activity. Numerous studies demonstrate that spending time in green spaces limits cardiovascular disease and respiratory problems while improving general health (2). Nature also influences air quality: it acts as a particle filter, especially during pollution peaks, by absorbing numerous pollutants such as NO2, SO2 and other small air particles.
At a smaller scale, urban trees help sequester CO2 and help limit greenhouse effect. Indeed, trees capture atmospheric carbon which is then stored within biomass and soils. Through photosynthesis, a large adult tree can store up to 360 kg of CO2 each year (3) in its branches and trunk, in the form of lignin and cellulose. This capacity nevertheless depends on its size and age. The Arbo Climat online tool, created by the ADEME, provides information about a planting scenario’s impact on carbon storage. (4)
In addition to being beneficial for health, nature in the city also plays a recreational role. Shared parks and gardens create opportunities for social interaction, particularly through educational and participatory events. These exchanges contribute to culture and education and participate to global efforts being made to protect nature. To quote Jacques-Yves Cousteau: « on protège ce qu'on aime, et on aime ce qu'on connaît » (in English: we protect what we love, and we love what we know").
Greener cities are extremely beneficial for its inhabitants, for the planet, but also for buildings’ value-creation. Humans have a natural tendency to seek connections with nature, a concept called Biophilia (5). The proximity of gardens and parks therefore offers added value to property assets. A study demonstrated that, in the city of Brest (France), the value of properties in direct proximity to green spaces was 17% higher than properties located just 100 meters away. It has been shown that when the density of green spaces increases by 10% in the city of Anger, properties’ value increase by 1.3% (6). It is important to mention that such figures can only vary from a city to another and depend on the size of the green space. It nevertheless demonstrates a genuine green trend within cities.
BiodiverCity® label: an important role to play
To benefit from all that natures has to offer, we must ensure that the best architectural solutions implement biodiversity within buildings, but also that we create varied and functional habitats. Green walls, nesting boxes or even green roofs should be studied based on an ecological diagnosis considering the project and its surrounding environment, thus improving the ecological continuity of the city.
The BiodiverCity® label is a guide to achieving these goals. It allows the successful integration of ecological features of a real estate project to be celebrated. The BiodiverCity® Label increases the importance of the “green spaces” technical package and the long-term management of these spaces. By the end of the certification process, it enables the performance of real estate operations to be displayed according to their level of consideration and value creation for biodiversity.
Supported by the International Biodiversity and Real Estate Council (CIBI), this label applies to new construction projects as well as major refurbishments operations. It focuses on all public and private buildings: offices, business parks and logistics parks, joint development zones, shopping centres, etc. It is therefore aimed at developers, architects, property owners, real estate managers and developers.
The certification process happens over 4 stages:
1. The project's commitment to the process, this phase must take place before filing the building permit;
2. The design phase, constitutes the major part of the work: the accredited BiodiverCity assessor works with the project owner to define the objectives and gather the evidence of conformity with the label;
3. The verification audit by an independent body, which verifies the report’s compliance;
4. When the report is compliant, the CIBI (brand owner) issues the certificate.
The benefits of the BiodiverCity® label include:
1. Promotion of the most ecological projects
2. Implementation of solutions for biodiversity allowing developers to create projects with higher added value
3. Stronger arguments in the eyes of elected officials
4. The guarantee of quality and reputation within a city.
The use of an ecologist accredited by the CIBI is imposed by the label. He/She will then play the role of specialist AMO, advisor and assessor. Following a biodiversity diagnosis, he/she will be proactive in improving the biodiversity aspect of the project. Longevity Partners, accredited BiodiverCity® assessor, will ensure the excellence of the ecological performance of buildings willing to integrate biodiversity at the heart of their projects.
(2) Mitchell R., Popham F., 2008. Effect of exposure to natural environment on health inequalities: an observational population study. The Lancet
(3) Jacquet, 2011. Performance énergétique d’une toiture végétale au centre-ville de Montréal. Centre d’écologie urbaine de Montréal.
(5) Edward O. Wilson, 1984. Biophilia, Cambridge, Harvard University Press.
(6) Choumert J., Travers M., 2010. La capitalisation immobilière des espaces verts dans la ville d'Angers, Revue économique 2010/5 (Vol. 61)