Soil quality and urban sprawl: Insights from long-term patterns in the Rome metropolitan region

The dynamics related to land take depend on the interaction of two factors: soil quality and anthropogenic actions and strategies. Soil as “living system” plays an active role in the phases of interaction between the components of ecosystems. Meanwhile, the soil is exposed to intense and constant human-induced degradation processes. The aim of this paper is to quantify the impact of urban expansion on soil quality in a Mediterranean urban area (Rome, Italy). Over an examined area of 1500 km2, urban areas increased by 5.9% per year (from 8.2% in 1949 to 36.6% in 2018). At that time, urban areas consumed high-quality soils in greater proportion compared to low-quality soils while croplands and forests progressively covered low-quality and partially degraded soils. Moreover, dispersed peri-urban settlements have been built in Rome on high-quality soils rather than in dense urban settlements, suggesting that the recent low-density urban expansion mainly affects soil quality and land resources. Those data show that sprawl consumes high-quality land at higher rate than compact growth, thus influencing the environmental quality of neighboring land. This case study, as an assessment and monitoring of soil quality over multiple timescales, is the basis on which any planning project can be built. It develops, in a scenario where, although significant progress in the analyses and assessments of land take has been achieved, it still appears as “open challenge” and it is not easy to work on a more effective decrease in land take and a consequent conservation of ecosystem functions and services.