Interactions between European buckthorn (Rhamnus carhartica) and invasive earthworms in the forests of Chicago, Illinois, are an elegant example of the potential implications of adopting a perspective based on alternative stable states, strong feedbacks, and resilience theory in urban ecological restoration (Heneghan et al. 2002, 2004, 2006). Buckthorn is a major invasive plant pest in the Chicago area, forming dense thickets that exclude native plants. In ongoing work to study the buckthorn invasion and restore affected woodlands, researchers noticed a convergence of high invasive earthworm biomass in buckthorn patches (Heneghan et al. 2006). Experimental work has identified a link between the nitrogen (N)-rich buckthorn litter and earthworms that has led to a synergistic invasional “meltdown,” (Simberloff & Von Holle 1999), where each Cities are important sites for restoration and reclamation activities. However, the nature of the urban environment alters urban soils through direct and indirect effects, presenting unique challenges with respect to the potential for, and the practice of, ecological restoration. Aspects of the urban landscape and soil conditions thus limit how far restoration can progress along a trajectory away from a degraded state (Lindig-Cisneros & Zedler 2000).
Unique soil conditions and novel urban soil taxonomy fundamentally change the nature of urban ecosystems, requiring strong manipulations and interventions to ameliorate urban environmental effects during restoration in cities. Drastic changes and degradation of soils require drastic actions, such as creating new soils and putting soils in novel places. Urbanization changes the dynamics of restoration, as urban soils possess many traits that promote the continued invasion of sites by undesirable and invasive species. The urban environment creates a system that is dominated by strong interactions and potential alternative stable states, which adds even more complexity to the practice of restoration in cities. Finally, these urban environmental effects in combination with the legacy of past land use creates a situation where there is a lack of suitable reference conditions for urban soil restoration.