A Treebog is a form of compost toilet which has willows and other nutrient-hungry plants planted around it. The faeces is held in a chamber open to the air which allows it to decompose rapidly, feeding the trees around it. Unlike a conventional compost toilet, a Treebog is usually not emptied or dug out when it eventually fills up the willows are simply left to feed on the compost and the superstructure rebuilt or moved to the adjacent patch of ground and willow cuttings replanted. Effectively, it is a system for converting human faeces to willow trees and soil biomass.