associates include white ash (Fraxinus americana), red maple (Acer rubrum), and northern red oak (Quercus rubra), which becomes less and less common northwards, dropping out almost entirely by mid-Vermont, New Hampshire, and inland Maine. White oak (Quercus alba) is also an important canopy species in southern New England's seaboard lowlands. White pine (Pinus strobus) and red pine (Pinus resinosa), are also an important part of this mixed forest. The pioneer trees of this forest are quaking aspen (Populus tremuloides) and paper birch (Betula papyrifera). Wetlands Wetlands are defined anywhere by an abundance of water, hydric soils, and a unique flora. The wetland of the New England area exhibit considerable diversity across the range and elevations within the three category: bogs, swamps, and bottomlands. Swamps and bogs are specific habitats whereas bottomlands are any moist area including riparian zones, lake and pond banks, and the moist area surrounding bogs, marshes and swamps. Bogs Bogs are wetland areas, characterized by acid hydric soils composed of peat. Bogs can occur at any elevation in this ecoregion. They are often sphagnum heath areas dominated by shrubs in the family Ericaceae including: leather leaf (Chamaedaphne calyculata), bog rosemary (Andromeda polifolia), Labrador tea (Ledum groenlandicum), bog laurel (Kalmia polifolia), and American cranberry bushes (Vaccinium macrocarpon). Throughout New England these areas are often artificially made for cranberry monocultures by commercial farms. Common components of the herb layer in bogs includes the carnivorous plants: round-leaved sundew (Drosera rotundifolia), and pitcher plant (Sarracenia purpurea). Other common herbs of the poor soils of bogs include false mayflower (Maianthemum trifolium), and some orchids, particularly, bog candles (Platanthera dilatata). The most common trees that invade bogs as they fill in are black spruce (Picea mariana), northern white cedar (Thuja occidentalis), larch (Larix laricina) and black ash (Fraxinus nigra). Swamps Swamps are typically characterized by hydric soils and have more of a canopy than bogs. The most characteristic trees of southern and low altitude New England swamps are hemlock (Tsuga canadensis), northern white cedar (Thuja occidentalis), tamarack (Larix laricina), balsam poplar (Populus balsamifera), red maple (Acer rubrum), atlantic white cedar (Chamaecyparis thyoides), tupelo (Nyssa sylvatica) and black ash (Fraxinus nigra). Often cool, moist shaded ravines are dominated by pure stands of hemlocks in this range. In northern and high altitude swamps of New England the dominant canopy species change to tamarack, black spruce (Picea mariana) and balsam fir (Abies balsamea). The understory across