The growth of cities and towns together with the associated increase in their ecological ‘footprint’ is one of the most serious ecological problems facing the world today. The increase in the number of people living in cities and towns, coupled with the magnitude and intensity of human activities, has resulted in what Likens (1991) refers to as human-accelerated environmental change. This includes changes in land use, toxification of the biosphere, invasion of exotic species and loss of biotic diversity. These changes are most evident in major cities, but significant changes are also occurring in peri-urban areas, in small towns and especially in coastal settlements. The rate of change associated with the expansion and creation of cities and towns is particularly high in developing countries (Lee, 2007). Human-accelerated environmental change is occurring at small and large spatial scales throughout the world, but the true magnitude of the impact of these changes is difficult to envisage because of uncertainties in the predicted effects of global climate change (IPCC, 2001).
We face many challenges and potential conflicts if we are to manage current day-to-day problems and attempt the bigger task of creating sustainable cities and towns in the future. Although cities and towns are dominated by human-built structures and activities (buildings, vehicles, impermeable surfaces, parks, etc.), they are functioning ecosystems that possess many of the same components (plants, animals, water, soil, etc.) and processes (i.e. nutrient and water cycling) as less human-dominated natural systems (McDonnell and Pickett, 1993b; Grimm et al., 2003).