Bison once roamed the United Kingdom freely, but like many native animals, agriculture and human development killed them all off. This month, for the first time in 6,000 years, three wild bison were released into a forest near Kent. The bison have been brought in as ecosystem engineers — they will thrash around the forest, eating bark and killing trees, eating and dispersing seeds, creating new habitats for other species and generally transforming a monoculture forest into a rewilded one, which should sequester more carbon from the atmosphere. As Richard Kemeny reports from Southeast England, environmentalists hope this will be the start of a new era of conservation in the UK.