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An urban wilderness refers to the inclusion of biodiversity in urban neighborhoods as a part New Urbanism movement.
Key traits of urban wilderness that differentiate it from lawns and other ecologically questionable forms of plantings are:
- Biodiversity - a wide range of species, both of plants and animals
- Minimal maintenance required for viability - plants that can survive without frequent waterings, can withstand local pollution levels, and do not depend on infusions of fertilizers or other periodic soil amendments (see xeriscaping)
- Deep beds - deep soil allowing the creation of mature root growth, protection from drought and destructive temperature changes, and the development of a healthy colony of microorganisms, worms, and other beneficial small lifeforms
- Native species - considered use of local varieties rather than exotic species
- Unstructured aesthetic - plants allowed to grow as they wish, where they wish, with minimal space devoted to paved walkways, trimmed grass, or other artificial environments
- Tolerance of groundcover and thick undergrowth - healthy ecosystems depend on "messy" microenvironments like decaying logs, thick brush, and muddy ground.
Urban wilderness has been created by programs as varied as the New York City Parks Department's Green Streets program (which converts median strips and other microenvironments into planted areas) and small programs in such places as Davis, California and Portland, Oregon to reintroduce native species.
The nineteenth and twentieth centuries saw the urbanization of cities, with minimal space set aside for living things. Jacob Riis and other reformers fought for parks in urban areas, but the resulting parks, while a vast improvement, were formalized, rectilinear arrangements of artificially orderly lawns, bushes, and walkways.
While many societies had traditions of intense urban plantings, such as the rooftops of pre-conquistador Mexico City, such traditions did not reemerge on a larger scale in the industrialized world until the creation of naturalistic urban parks, such as the ones by Calvert Vaux and Frederick Law Olmsted. The rise of the City Beautiful Movement enhanced this trend as American, European, and other cities worked to bring natural settings back into urban areas.
Actions done by activists from groups such as squatters and Reclaim The Streets are engaged in guerrilla plantings, from work done in or on abandoned buildings to tearing holes in highway asphalt and then filling the holes with soil and flowers. These actions have been particularly effective in creating new planted zones in economically decimated areas like urban eastern Germany, where abandoned buildings are occasionally reverted to forest-like conditions. However, this trend can work so well that they become targets for gentrification, with thirty-foot (ten meter) trees grown over building foundations being torn down for yet more high density development.