Impacts of soil de-sealing practices on urban land-uses, soil functions and ecosystem services in French cities

Soil sealing has been recognised as one of the main causes of urban soil degradation in Europe. To tackle this issue, de-sealing measures have recently been promoted in cities to increase the sustainability of soil ecosystem services. To our knowledge, very few evaluations of de-sealing projects have as yet been done to assess the current framework of these urban planning practices. Therefore, we conducted an online survey to collect and analyse soil de-sealing projects throughout mainland France. A 60-question survey was run over a 4-month-period, and data about 57 projects were collected. The answers covered a diversity of projects, structures and stakeholders and included data such as the location / objectives / costs and benefits of the projects implemented in cities of various sizes. A typology of urban land-uses before and after de-sealing was defined. Among the diverse objectives of de-sealing, rainwater management, reducing urban heat, and greening were most frequent. More than half of the respondents (64%) indicated that ecosystem services were used to drive their de-sealing project. The methods usually required excavation of the sealing cover and road layers being replaced by newly imported fertile materials. Recent de-sealing projects have reused derelict materials from the site (soil-material inventory) and/or local urban waste for soil construction, which can help minimise both the economic and environmental costs of urban greening projects. The results of this study provide quite an exhaustive view of current French de-sealing practices and could provide guidelines for improving soil functions by applying soil engineering processes to construct sustainable fertile soils for urban greening.