Oak-Hickory Forests: Extent and Description

Distribution

The upland oak-hickory forest type occupies nearly 114 million acres (46.1 million ha) of commercial forestland in the eastern United States-more than any other single forest type in the country, excluding types in Alaska (USDA Forest Service 1980). It is found along the prairie borders from Texas north to the Dakotas, eastward throughout the Central States and Appalachian region into southern New England, and from the northern hardwood transition zone southward into the Piedmont Plateau and Coastal Plain. The type is well developed in the Cumberland Plateau and portions of the Appalachian Mountains and most continuous in the Ozark and Ouachita Highlands (Fowells 1965).

Soil types

Within this vast area oak-hickory occurs on soils ranging from cool-moist Boralf and Orthod Spodosols to warm-dry Mollisols and Alfisols. These soils are derived from glacial material, residual sandstone, shales, and limestones and from gneisses, schists, and granites and range from clay to loamy. The type is found on all topographic positions from dry rocky ridges to deep coves to well-drained valley floors (Fowells 1965).

Climate

The climate over the range of the oak-hickory type is humid except in the southwestern fringe where it is moist subhumid to dry subhumid. Average annual precipitation is 22 inches (560 mm) in central Texas, from 30 inches (760 mm) to 40 inches (1015 mm) in the Central States, and about 80 inches (2030 mm) in the southern Appalachians. Generally, about one-half or more of the annual precipitation falls in the dormant season, and from 2 to 8 week periods with little or no rainfall are common late in the growing season, particularly in the western part of the range. Average annual snowfall is 100 inches (2540 mm) or more in the North, from 15 to 20 inches (380 to 510 mm) in the Central States, and a trace in the South. Mean annual temperature averages 40° F (4.4° C) in the North, 55° F (12.8° C) in the Central States, and 65° F (18.3° C) in the South. The frost-free period averages 100 days in the North, 180 days in the Central States, and 290 days in the South (Fowells 1965).

Major species

Within the broad oak-hickory type, the Society of American Foresters has defined nine forest cover types as oak types. Oaks and hickories are also listed as components of 31 other forest cover types (Eyre 1980). The great range of climate, soil, and topography results in widely different stand compositions. White oak (Quercus alba L.), northern red oak (Q. rubra L.), and black oak (Q. velutina Lam.) are found throughout the type. Other common oaks on drier sites are scarlet oak (Q. coccinea Muenchh.) and chestnut oak (Q. prinus L.) in the Appalachians and adjoining areas; northern pin oak (Q. ellipsoidalis E. J. Hill) and bur oak (Q. macrocarpa Michx.) in the northern and western parts of the range; and post oak (Q. stellata Wangenh.), blackjack oak (Q. marilandica Muenchh.), bluejack oak (Q. incana Bartr.), and southern red oak (Q. falcata Michx.) in the West and South. Pignut hickory (Carya glabra (Mill.) Sweet), mockernut hickory (C. tomentosa (Poir.) Nutt.), shagbark hickory (C. ovata (Mill.) K. Koch), and bitternut hickory (C. cordiformis (Wangenh.) K. Koch) are consistent but minor components of the type.

The mixture may also contain yellow-poplar (Liriodendron tulipifera L.), ashes (Fraxinus L. spp.), elms (Ulmus L. spp.), sugar maple (Acer saccharum L.), red maple (A. rubrum L.), blackgum (Nyssa sylvatica Marsh.), black locust (Robinia pseudoacacia L.), black cherry (Prunus serotina Ehrh.), black walnut (Juglans nigra L.), and many other hardwood species. On suitable sites, shortleaf pine (Pinus echinata Mill.), loblolly pine (P. taeda L.), pitch pine (P. rigida Mill.), Virginia pine (P. virginiana Mill.), eastern white pine (P. strobus L.), eastern hemlock (Tsuga canadensis (L.) Carr.), and eastern redcedar (Juniperus virginiana L.) may also be present. The oak-hickory type often grades into the oak-pine type in the Piedmont Plateau (Braun 1950).

Understory species

Many species of understory trees and shrubs occur in oak-hickory stands. Some of the most common ones are flowering dogwood (Cornus florida L.), gray dogwood (C. racemosa Lam.), sassafras (Sassafras albidum (Nutt.) Nees), sourwood (Oxydendrum arboreum (L.) DC.), eastern redbud (Cercis canadensis L.), downy serviceberry (Amelanchier arborea (Michx. f.) Fem.), blueberry (Vaccinium L. spp.), mountain laurel (Kalmia latifolia L.), witch-hazel (Hamamelis virginiana L.), beaked hazel (Corylus cornuta Marsh. var. cornuta), and bramble (Rubus L. spp.) (Braun 1950, Fowells 1965).