There Goes the Neighborhood
Mckinney, Michael L., Forum for Applied Research and Public Policy
Urban sprawl must be added to the long list of human impacts that threaten a massive modern extinction.
Population growth, wasteful patterns of consumption, and diminishing natural resources are rapidly pushing many species to the brink of extinction. Even biologists have difficulty assessing the complexity and speed of human impacts on the biological world.
In the United States, many native species were initially threatened mainly by overhunting: the killing of large game species beyond their capacity to reproduce. The buffalo disappeared from the eastern United States in the early 1 800s, and elk, panthers, wolves, and a few other large species disappeared by the middle part of that century.  Though some species, such as wolves, are recovering, others, like the passenger pigeon, are gone forever.
The second stage of human impact in the United States, as in most nations, was the rapid transformation of the natural landscape by human settlements, especially the clearing of land for timber and agriculture. This led to extinction from habitat loss. Especially hard hit were species adapted to ancient, old-growth forests, prairies, river valleys, and other areas favored by farmers for growing foods.
The United States is now entering a third, and potentially much more devastating, stage of impact on native species. This is the transformation of the landscape by the geographic expansion of suburban areas into surrounding ecosystems, which is occurring at an alarming pace.  This urban expansion has many names, including urban sprawl, development, suburbanization, and counter-urbanization. Whatever the name, it is driven by the migration of people from very dense concentrations in cities to outlying areas where people are much more widely dispersed across the landscape. Urban sprawl therefore greatly magnifies human impacts per person on the environment because the dispersed inhabitants require a vast infrastructure of roads, parking lots, housing subdivisions, and many other physical transformations. It is not widely appreciated how much more harmful to natural ecosystems these urban transformations are than traditional farming and other rural land uses that allowed many native species to persist and ev en flourish.
Urban sprawl produces the local equivalent of a mass extinction. It eradicates over 90 percent of native species in the area, replacing them with a few non-native species that often become abundant pests because they lack natural enemies. Even worse, the impacts of urban expansion are so dramatic and persistent that it will take many decades and probably centuries for natural systems to recover, assuming they ever get the chance. In brief, the current model for the expansion of cities is the terminal--in both senses of the word--stage of human impact on natural ecosystems.
Ironically, urban sprawl is driven in large part by the desire of urban inhabitants to experience more natural surroundings. Indeed, there is a strong positive statistical correlation between household income and the number of native species still surviving in a housing development.  People clearly prefer natural surroundings when they can afford them. Implicit in this irony, however, is an important source of optimism: if suburbanites can become more educated, they are likely to take steps to reduce the harm done to native ecosystems. In fact, many of these steps are painless, even money-saving activities, such as resisting the urge to destroy small wetlands--which reduce storm flooding--and planting native species, which saves considerable lawn maintenance.
There is a growing realization that federal laws such as the Endangered Species Act, intended to protect species, have failed to fulfill their promise. Therefore, promoting biodiversity at local levels may be the strongest weapon against extinctions, since the policy decisions causing most extinctions in the United States are made at the local level by developers, individual landowners, conservation alliances, and local and state governments. …