Historical accounts and descriptions of the Boston Harbor Islands were searched for references to the islands' vegetation. They indicate dramatic changes in vegetation structure and composition since 1600. Many of the islands were wooded prior to European settlement, although Native American use is evident before 1600. Forests were cleared for agriculture, building materials, and firewood. Through the centuries since European settlement, the islands have variously supported municipal and military facilities, some of which have since been abandoned. As use of the islands changed, the vegetation of the islands also changed; in some cases native trees and other species returned to abandoned areas, while in others new, exotic species became established or were planted. By the end of the 20^th century the vegetation had become a mixture of woodlands (roughly 25% of the islands as a whole), shrub thickets, open lands, and manicured landscapes, all of which include a large component of non-native species.