New England–Acadian forests

Alpine communities are essentially regions of Arctic tundra, or treeless tundra-like communities. These are restricted to the tops of mountains that reach above the tree line, about 1300 metres (4,265 feet).

Mountaintops of Nova Scotia's Cape Breton Island (highest point 1,755 feet) may have minor alpine biota, krumholtz and other aspects, as do many other smaller isolated peaks throughout the region. Full-blown alpine communities are found on Washington and the other White Mountains of New Hampshire and on Mount Katahdin in Maine. Quebec's Gaspé Peninsula, vegetatively similar to Maine and New Brunswick, also has extensive treeless uplands—which are rare in the region.

These tall mountains serve as refugia for arctic plants left over from the retreat of the Laurentide glacier at the end of the last ice age (the Wisconsin glaciation). The truest alpine tundra communities are located on the harsh western and northwestern slopes of tall mountains. The western slopes are typically heath dominated communities composed of plant of the family Ericaceae, changing to grasses and sedges toward the harsher northwestern faces. Common dominant components of the heaths are alpine bilberry (Vaccinium uliginosum) and mountain cranberry (Vaccinium vitis-idaea).

Coniferous forests are found in the White Mountain regions and the northern parts of New England Uplands, primarily the middle interior of Maine and northwards and especially in areas between 1300 metres (4,265 feet) and 900 metres (2,953) feet ) elevation. It is also found on parts of the Fundy coast in Maine and the Maritimes, the northern parts of this ecoregion where the summers are cool. The coniferous forest goes by many names, including: Boreal forest, fir-spruce forest, the North Woods, and the taiga. It is noted in New England for its "harsh" conditions such as cold, subarctic temperatures, a short growing period, sandy-gravely acidic soil, and a high rate of leeching of nutrients out of the soil. It is also noted for a high rate of precipitation, year round, as rain and snow, which contributes to much of the leeching.

The dominant canopy species of this area include red pine (Pinus resinosa), balsam fir (Abies balsamea), paper birch (Betula papyrifera), red spruce (Picea rubens), which northwards, is replaced by white spruce (Picea glauca). Also present are jack pine (Pinus banksiana), and white pine (Pinus strobus) which is found in areas of richer soil in the lower elevations of this forest. The presence of paper birch (Betula papyrifera), a successional species, is often an indication of past disturbances such as fire or logging in the forest.

Typical woody understory and shrub layer species include moosewood (Acer pensylvanicum), low-bush blueberry (Vaccinium angustifolium) and other heath species, especially the genera Gaylussacia and Vaccinium.

Woody plants of the ground cover layer include American wintergreen (Gaultheria procumbens) and partridge berry (Mitchella repens). Common wildflowers include star flower (Trientalis borealis), bluebead Lilly (Clintonia borealis), foam flower (Tiarella cordifolia), bunchberry (Cornus canadensis), twinflower (Linnaea borealis), dewdrops (Dalibarda repens), wild sarsaparilla (Aralia nudicaulis), and Canada mayflower (Maianthemum canadense). Trilliums, and yellow lady slippers (genus Cypripedium) are also common showy wildflowers. The herbaceous layer also includes many mosses, lichens, and ferns. Bracken fern (Pteridium aquilinum) is often particularly abundant in these communities.

These forests also go by the names: hemlock-northern hardwoods, and mixed forests. The northern hardwoods are located in the seaboard lowlands and south of the coniferous forests, but there is considerable blending of the two communities. These forests are typical of elevations below 700 m. Elements of these communities mix extensively with coniferous forest elements between 700 m and 900 m, and also from mid-latitude Vermont and New Hampshire north to central Maine where coniferous forest elements begin to dominate. Typically the richer the soils, and the more temperate the climate, the more dominant hardwoods will be. This forest type is considered the northern extension of the mixed mesophytic deciduous forest. The four dominant canopy species of the hemlock-northern hardwood forests are sugar maple (Acer saccharum), beech (Fagus grandifolia), yellow birch (Betula alleghaniensis) and hemlock (Tsuga canadensis). Other common canopy 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 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 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 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 the range consists of a number of Viburnum species, among others.

The bottomlands and margin areas in the northern hardwood communities are primarily dominated by: red maple (Acer rubrum), balsam poplar (Populus balsamifera), black ash (Fraxinus nigra), eastern cottonwood (Populus deltoides), and the silver maple (Acer saccharinum). The bottomlands and margin areas of the coniferous forests consist of: red maple, silver maple, white cedar, and balsam poplar. In wet areas throughout the region many sub-canopy species of willow (Salix spp.) occur, as does speckled alder (Alnus rugosa), which is very common.