OUR COMMON SOILS: West Lausanne Urbanization as Anthropedogenesis, A Section through the Spaces and Times of Urban Soils

Motivated by ever-increasing soil degradation and artificialization due to past and present urban growth dynamics, the current trend of spatial planning policies at the European and Swiss levels is promoting increased soil protection, by avoiding new developments on agricultural and natural land, and by reorienting development towards existing urban areas that must be densified and restructured. This objective, which is formulated as "inward urbanization", not only puts pressure on the soils situated within urban areas, which are cast as priority development targets, but also gives a strategic role to this significant component of anthropogenic ecosystems, the multifunctionality of which must be considered as a crucial driver facing cities forthcoming social-ecological transition. However, urban soils are insufficiently studied as a long-term record of environmental history and heavy anthropization. In this context, the originality of this research is to consider urbanization not only as consuming and degrading, but also as transforming and producing soils, and to provide a methodology for the study of anthropedogenesis as a coevolution process of urban forms and soil functionalities, in both retrospective (history) and prospective (project) perspectives. Thus spatial development and urbanization do not only appear as a threat to soil capital but also as a key lever on which it is possible to act in order to valorize this resource. Based on a case study in fast-growing West Lausanne mixed-use district (Switzerland), this PhD thesis investigates the extreme qualitative variability of urban soils by presenting a conceptual model, a set of cartographic layers and profile descriptions. These research operations highlight soil evolution processes as a value which co-variates with Swiss Plateau city-territory urbanization. The various layers and map series of an Atlas of Urban Soils underscore the applicability of different types of information for documenting the combined influence of native geomorphology, anthrosediments and land cover changes, through various spatial and quantitative analyses. Complemented by empirical Urban Soils Portraits, such a consolidated concept map defines a template on which to apply the state factor and process-response approaches. Instead of using a simple spatial transect or time gradient, contrasting urban soil development pathways and their resilience are explained, mapped and quantified in the form of a complex spatiotemporal anthroposequence, and as a coherent bundle of historical trajectories and systematic patterns. Such a narrative integrates various facets of land use, integrating one-off construction techniques and recurring maintenance practices, planning tools, and morphologies, into a specific 'project for the ground' which brought forth the mixed-use mesh of the Swiss Plateau city-territory. Ultimately, in light of the ongoing planning policies, the dynamic vision conveyed by these intertwined soil-urbanization coevolution trajectories outlines opportunities and strategies for the regeneration of the resource deposit made up of both West Lausanne urban fabric and its soils. Such opportunities and strategies, which aim at a sustainable implementation of the inward urbanization principle, rest on the understanding of both the city-territory and its urban soils as palimpsests forming a dynamic system.