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ABSTRACT
Urban habitats are characterized by high levels of disturbance, impervious paving, and heat retention. These factors, acting in concert, alter soil, water, and air conditions in ways that promote the growth of stress-tolerant, early-successional vegetation on abandoned or unmaintained land. In most urban areas, a cosmopolitan array of spontaneous plants provide important ecological services that, in light of projected climate change impacts, are likely to become more significant in the future. Learning how to manage spontaneous urban vegetation to increase its ecological and social values may be a more sustainable strategy than attempting to restore historical ecosystems that flourished before the city existed.
KEYWORDS
climate change, disturbance, globalization, preadaptation, ruderal vegetation, urbanization, wasteland
Urban ecology can be distinguished from its natural systems counterpart by the inseparable blend of human culture and natural history. Mastering the discipline requires dealing not only with issues related to the quality of air, water, and soil as modified by humans, but also with the complex economic, social, and cultural systems which dictate the flow of energy and raw materials throughout metropolitan areas (Alberti et al. 2003; Gilbert 1989; Grimm et al. 2000). In cities, human values-driven mainly by socio-economic considerations-typically trump biological factors such that people encourage the pres - ence of organisms that make the environment a more attractive, livable, or profitable place to be, and vilify as weeds and pests those that flourish in contradistinction to these goals.
From a strictly functional perspective, most vegetated urban land can be classified into one of three broad categories: remnant native landscapes, managed horticultural landscapes, and abandoned ruderal landscapes (Kowarik 2005; Kühn 2006; Whitney 1985; Zipperer et al. 1997). These landscape types can be distinguished from one another on the basis of 1) their past land-use history; 2) the types of vegetation they contain; 3) the characteristics of their soils; and 4) the levels of maintenance they require in order to preserve their integrity (Table 1). The least studied of these types, and the focus of this paper, is the abandoned ruderal landscape which consists of marginal or degraded urban land that receives little or no maintenance and is dominated by spontaneous vegetation-a cosmopolitan mix of species that grows and reproduces without human care or intent. Ruderal landscapes are...