Ecological restoration is subject area within
landscape ecology concerned with restoring
ecosystems to a more natural state. Wetland restoration, restoration of industrial sites, and urban stream corridors are common types of ecological restoration sites.
There tends to be a lot of discussion within the area of what really qualifies as a restoration; the current accepted definition of a restoration is that it returns a site to a specific point in time; for example, as a place was before European contact. The same definition is used in historic preservation, a restoration returns a building or site to the way it was at a specific point in time or a specific period or time.
A related discussion within the field of ecological restoration questions whether or not it is possible to actually accomplish that goal. Being that the restoration is a created nature, which is undoubtedly affected by our beliefs and points of view at the time of it's creation, can it possibly ever become truly "nature" again?
See Ecological Restoration magazine, Volume 19, Number 1, Borges and the Restorationsist's Dilemma, for a very funny discussion of this paradox.