TEMPERATE DECIDUOUS FOREST BIOME

The temperate deciduous forest biome occupies most of the eastern part of the United States and a small strip of southern Ontario. Precipitation varies from 28 inches per year in the northwestern section of the biome to 60 inches per year in the southeastern part; in most areas the precipitation is distributed evenly throughout the year. Frost occurs throughout the biome, and summer and winter are distinct seasons.

The dominant plant species of the biome are broad-leaved deciduous trees. Because the biome covers such a large geographical area, large differences have led to the recognition of eight major forest regions within the biome, each dominated by a different species or association of species. These are: mixed mesophytic, Appalachian oak, hemlock-white pine-northern hardwoods, oak-hickory, maple-basswood, beech-maple, oak-pine, and southern pine.

The mixed mesophytic forest region is in the centrally located and topographically diverse Appalachian and Cumberland Plateaus. Geologically, it is the oldest region in the biome and is the most complex and highly developed biotically. Nearly all the dominant species in the entire biome are found here, and many reach their maximum development here. The mixed mesophytic region is thought to be the center of dispersal from which the other forest regions in the biome were formed. In all, there are about 30 tree species which assume dominance in the region; however, in most areas dominance is shared by two or three of these species, depending on differences in microclimate and other factors. Yellow buckeye (Aesculus octandra) and white basswood (Tilia heterophylla) are the most constant dominants and are considered the indicator species for the region. Other common dominants include yellow-poplar (Liriodendron tulipifera), American beech (Fagus grandifolia), cucumber magnolia (Magnolia acuminata), sugar maple (Acer saccharum), white oak (Quercus alba), and eastern hemlock (Tsuga canadensis).

The Appalachian oak forest region lies to the east, north, and southeast of the mixed mesophytic forest. Geologically, it is characterized by a system of parallel valleys and ridges. Northern red oak (Quercus rubra) and white oak are the two major species in the region.

White oak reaches its maximum development on deep, rich soils of coves and high bottomlands, but grows well on all but the driest and wettest sites in the region. The success of white oak is attributed to its ability to survive for long periods as an understory species, its quick and vigorous response to release from this suppression, and its great longevity (often reaching 400-600 years). The ecologically similar red oak occupies sites which are usually slightly drier or wetter than those dominated by white oak. Chestnut oak (Q. prinus) is a third important species of the region and forms an edaphic climax with post oak (Q. stellata) and blackjack oak (Q. marilandica) on rocky, dry ridges. The American chestnut (Castanea dentata) was another important dominant in the region until eliminated by a bark fungus in the early 1900's. Sugar maple is the climax species on very rich sites, while American beech dominates the cove forests too moist for white oak and tulip-poplar. Pitch pine (Pinus rigida) is a common successional species.

The hemlock-white pine-northern hardwood region is situated along the northern edge of the biome, bordering the northern coniferous forest. Eastern hemlock (Tsuga canadensis) is one of the most tolerant of all trees and survives under very low light conditions. Eastern white pine is varied in its occurrence with other species and in its ecological role in the region. In the Lake States it often forms extensive pure stands of on drier sites mixes with red pine and jack pine. On heavier soils characteristic of the East, it occurs mainly as scattered individuals amongst a predominantly hardwood forest. Sugar maple, American beech, white ash (Fraxinus americana) and yellow birch (Betula alleghaniensis) are the most common hardwoods in the region. Paper birch (B. papyrifera) is a common early successional species in the eastern part of the region, while aspen (Populus tremuloides and P. grandidentata) and jack pine assume this role in the Lake States (along with paper birch).

The oak-hickory forest region occupies drier areas to the west of the mixed mesophytic forest region. Drought-resistant oaks and hickories are the most common trees species. The principal oaks are white oak, northern red oak, and black oak (Q. velutina), while bur oak (Q.
macrocarpa), blackjack oak, shingle oak (Q. imbricaria) and overcup oak (Q. lyrata) are also common. The most important hickories are bitternut (Carya cordiformis) and shagbark (C. ovata), while shellbark (C. laciniosa), mockernut (C. tomentosa), and pignut (C. glabra) occur more frequently on the drier upland soils. The trees commonly found scattered throughout the stream and river valleys of the region (and indeed nearly all regions in the biome) are American elm (Ulmus americana), American sycamore (Platanus occidentalis), hackberry (Celtis spp.), silver maple (Acer saccharinum), river birch (Betula nigra), and eastern cottonwood (Populus deltoides). These riparian trees are generally fast-growing, shallow-rooted, relatively large, and able to withstand repeated floodings throughout the year. A savanna-like transition zone is formed along the western edge of the oak-hickory region where the temperate deciduous forest biome grades into the temperate grasslands biome. Here bur oak, the most drought resistant of all (eastern) oaks, occurs as scattered trees amongst the grassy plains.

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