Characterisation of the urban brown network - Tram’BioSol project

On a global scale, soils are one of the most important reservoirs of biodiversity, accounting for 25-30% of the Earth's total biodiversity. . Soil biodiversity in temperate zones, which represents only 0.25% of soil mass, is made up of millions of species and billions of individuals, with microorganisms representing the largest group (66%) in terms of diversity, abundance and biomass, while invertebrate species of the microfauna, mesofauna and macrofauna account for only 33%. .

Although considered to be the fragile skin of the earth, soils are being degraded by human activities, and the many functions associated with them are under threat. These threats to soil multifunctionality are varied in nature: erosion, compaction, contamination, loss of organic matter or salinization. They are all the more acute in urban environments, where the pressures exerted by human beings are considerable, even leading to the disappearance of soils and/or their sealing. In particular, due to the development of our urbanization and infrastructures, 25,000 ha of soil are artificialized in France every year to meet the needs of a population that is now 80% urban. . Artificialization consists in transforming natural, agricultural or forest land, through development operations, in order to use it for housing or transport purposes. Artificialization thus leads to the lasting alteration of all or part of the ecological functions of natural soils, with the level of functional degradation varying according to the nature of the anthropogenic modifications to which the soil has been subjected. Soils may be only slightly affected by human activity, with only superficial impacts, or they may be totally destroyed by excavation.

On a European scale, soil artificialization has been recognized as a major cause of soil biodiversity erosion*. . The latter is...