Much of our understanding of the role urban soils play in ecosystem functioning is limited to characterizing soils near the surface ( 15). ![]() As a result, one of the major needs to fulfill an increased demand for urban ecosystem services is greater knowledge of urban soils as a critical component of environmental sustainability ( 12) and an integral asset in ecological urban management schemes ( 3, 13, 14). Thus, ecosystem structure and function are viewed as more integral to understanding how to manage urbanization ( 9), as they form the basis for ecosystem services ( 10, 11). In the contemporary urban era, ecosystem services-the benefits to people provided by natural system functioning-are valued. Knowledge of urban soils was focused on geotechnical engineering concerns to support built infrastructure. Past eras used urban development as a means to overcome barriers and problems created by natural system functioning ( 7, 8). Because most soil knowledge was developed in agricultural and wildland contexts, understanding of urban soils is limited ( 6). One of the significant changes with urbanization is the modification of soils ( 3 – 5). ![]() Urban population growth has greatly increased the extent of urban land globally ( 2). Between 1950 and the present the world’s urban population has grown by ∼3 billion people, and an additional three billion are anticipated by 2050 ( 1). One of the most significant drivers of land use and land cover change is urbanization. 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. 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. Urban soils also deviated from the standard A-B-C horizon ordering at a much greater frequency than preurban soils. 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). 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. 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. 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. Urbanization processes modify ecosystem function by changing the layers of soils identified as soil horizons. Soils support terrestrial ecosystem function and therefore are critical urban infrastructure for generating ecosystem services.
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