Rewilding is the restoring of land to the habitats and ecosystems that existed before it was altered by human activity. It can include the removal of most disruptive human activities and artifacts, such as buildings, roads, dams and agriculture, the removal of alien species, and the reintroduction and protection of lost native species, including apex predators and keystone species. Successful rewilding projects are self-regulating and require little human intervention other than to control encroachment of alien species and prevent the reentry of disruptive human activities.