Tree houses or tree forts, are platforms or buildings constructed around, next to or among the trunk or branches of one or more mature trees while above ground level. Tree houses can be used for recreation, work space, habitation, observation or as temporary retreats. In some parts of the tropics, houses are either fastened to trees or elevated on stilts to keep the living quarters above the ground to protect occupants and stored food from scavenging animals. The Korowai, a Papuan tribe in the southeast of Irian Jaya, live in tree houses, some nearly 40 metres high, as protection against a tribe of neighbouring head-hunters, the Citak. Along with subterranean and ground level houses, tree houses are an option for building eco-friendly houses in remote forest areas, because they do not require a clearing of a certain area of forest. The wildlife, climate and illumination on ground level in areas of dense close-canopy forest is not desirable to some people.