The mild climate, ample rain, and long growing season in Britain support a great variety of plants, which grow exceptionally well. Sometimes plant growth is compared to the lush areas of the well-watered and mild coasts of the states of Washington and Oregon. Most of Britain was once covered with thick, deciduous forests in which oak trees predominated. (Deciduous trees are those that lose their leaves every year.) The impact of centuries of dense human population has massively altered the flora of Britain, and only tiny remnants of these forests remain today. Although 9.9 percent of Britain is still forested, most of this area consists of commercially planted, fast-growing coniferous forests in Wales and northeastern Scotland. (Coniferous trees are evergreen trees that have cones.)
Before they were affected by centuries of clearing and human use, the great oak forests spread over the best soils in Britain. Forests were unable to establish themselves in the poorer soils of the mountains, wetlands, heath, and moorlands. The plants common to these wilder areas are heather, gorse, peat moss, rowan, and bilberry. These regions have been altered by heavy grazing of livestock and by controlled burning. Controlled burning creates environments suitable for game birds, which feed on the shoots of the new plants that spring up after the older plants are burned away. Some wetland areas have been subjected to massive draining efforts for hundreds of years and are now covered by towns and farmland. The marginal wetlands that remain continue to be threatened by reclamation for farms and homes, and some wetland plant species now grow only in conservation areas.