This article brings together the concepts of shrinking cities—the hundreds of cities worldwide experiencing long-term population loss—and ecology for the city. Ecology for the city is the application of a social–ecological understanding to shaping urban form and function along sustainable trajectories. Ecology for the shrinking city therefore acknowledges that urban transformations to sustainable trajectories may be quite different in shrinking cities as compared with growing cities. Shrinking cities are well poised for transformations, because shrinking is perceived as a crisis and can mobilize the social capacity to change. Ecology is particularly well suited to contribute solutions because of the extent of vacant land in shrinking cities that can be leveraged for ecosystem-services provisioning. A crucial role of an ecology for the shrinking city is identifying innovative pathways that create locally desired amenities that provide ecosystem services and contribute to urban sustainability at multiple scales.

Soils support terrestrial ecosystem function and therefore are critical urban infrastructure for generating ecosystem services. Urbanization processes modify ecosystem function by changing the layers of soils identified as soil horizons. Soil horizons are integrative proxies for suites of soil properties and as such can be used as an observable unit to track modifications within soil profiles. Here, in an analysis of 11 cities representing 10 of the 12 soil orders, we show that urban soils have ∼50% fewer soil horizons than preurban soils. Specifically, B horizons were much less common in urban soils and were replaced by a deepening of A horizons and a shallowing of C horizons. This shift is likely due to two processes: (i) local management, i.e., soil removal, mixing, and fill additions, and (ii) soil development timelines, i.e., urbanized soils are young and have had short time periods for soil horizon development since urbanization (decades to centuries) relative to soil formation before urbanization (centuries to millennia). Urban soils also deviated from the standard A-B-C horizon ordering at a much greater frequency than preurban soils. Overall, our finding of common shifts in urban soil profiles across soil orders and cities suggests that urban soils may function differently from their preurban antecedents. This work introduces a basis for improving our understanding of soil modifications by urbanization and its potential effects on ecosystem functioning and thereby has implications for ecosystem services derived from urban landscapes. Significance As societies move toward nature-based infrastructure to provide ecosystem services for sustainable urban environmental management, knowledge of urban soils remains a critical gap. An 11-city comparison of urban to reference preurban soil profiles revealed how urbanization modifies the presence and ordering of soil layers and its properties. Urban soils had fewer horizons than their preurban counterparts, with a predominant absence of intermediate B horizons. The loss of B horizons, which are not easily replaced, as they form over decades to millennia, can affect ecosystem functions, with potentially wide-ranging consequences for ecosystem services in cities.

Shrinking cities are widespread throughout the world despite the rapidly increasing global urban population. These cities are attempting to transition to sustainable trajectories to improve the health and well-being of urban residents, to build their capacity to adapt to changing conditions and to cope with major events. The dynamics of shrinking cities are different than the dynamics of growing cities, and therefore intentional research and planning around creating sustainable cities is needed for shrinking cities. We propose research that can be applied to shrinking cities by identifying parallel challenges in growing cities and translating urban research and planning that is specific to each city’s dynamics. In addition, we offer applications of panarchy concepts to this problem. The contributions to this Special Issue take on this forward-looking planning task through drawing lessons for urban sustainability from shrinking cities, or translating general lessons from urban research to the context of shrinking cities.