Physiography—Moving from east to west, upon leaving the Piedmont province one encounters the Blue Ridge and the Ridge and Valley provinces, and the Appalachian plateaus. The Blue Ridge Mountains, a belt 5 to 80 miles wide, extends from beyond the northern extremity of the southern Appalachians in Virginia southward to Georgia. This is the province through which passes the Appalachian Trail, the uninterrupted footpath from Maine's Mt. Katahdin to Springer Mountain in Georgia.12 This is also the region of the most rugged topography east of the Rocky Mountains, ordinarily rising 1000 to 4000 feet above the Piedmont and reaching an elevation of 6684 feet at Mt. Mitchell in North Carolina. The Blue Ridge is broadest and highest at its southern extremity. A twist in the general lay of the land orients the Great Smoky Mountains in the south in an east-west direction, in contrast to the general position of North American mountain ranges. (The Ozark and Ouachita mountains are other exceptions.)
North of the Roanoke River, the province appears as a single ridge, or a major one flanked by lesser ridges. Here the Blue Ridge got its name, for the haze on the mountains, caused by the terpenes exuded from the coniferous vegetation and accompanied by natural temperature inversions, gives the air a distinctly blue tint. Settlers named the Great Smoky Mountains for a similar reason.
Southward from the Roanoke River, closely spaced ridges form a rugged topography with a prominent escarpment that overlooks the Piedmont at elevations of 1500 to 2500 feet. Here the name Blue Ridge is applied locally only to the escarpment and to the ridges forming the divide between the Atlantic and Mississippi drainages. Other names, like Shenandoah and Catoctin, more specifically delineate sections of the Blue Ridge Mountains.
The Southern Appalachian chain of highlands contributes a great measure of character and culture to the southern forest. The physiography of the zone, geologically the oldest mountains of the continent, is largely responsible for the climate and soil that resulted in the complex and diverse vegetation covering the hills and valleys. The rugged terrain, discouraging to some elements of society, was the great enticement for others, especially the Scotch-Irish, who craved the isolation of the ridges and coves. Remote in communication, the lands provide a habitation for a people preferring isolation even to this day. Their forebears had come "unto a good land," not greatly
different in its physiography from that left behind on the British Isles. Here, in contrast to the long-ago cutover lands of Europe, were vast ranges of virgin, or near-virgin, forest.
From that good land the immigrants learned to utilize the varieties of wood, each for its highest use. For instance, a craftsman of the Civil War period, in making a "secretary" desk, used principally chestnut, with the desk's writing area inlaid with black cherry, the book shelves oak, and the back and hidden drawer parts basswood. The variety of woods and the soils enabled the handy settlers to be self-sufficient, so they required little contact with the world beyond the ridges.
Climate—Average precipitation for the Southern Appalachian provinces is between 40 and 60 inches, except at the highest elevations, where it exceeds 80 inches. High in the mountains, much precipitation falls as snow. The varied topography causes local precipitation patterns, rain shadows forming because of the proximity of the mountains and lesser hills. Annual precipitation within the zone may vary by more than 10 inches. Precipitation from a single storm over a two-hour period often differs by 3 inches when measured in gauges less than 100 feet apart.
For the whole of the Southern Appalachians, temperature effectiveness has been measured from less than 400 in the high-elevation reaches of the spruce and fir forests to 600 in the southerly and elevationally lower area. The spruce and fir sites occurring above 5500 feet in North Carolina and
Tennessee have growing season averages 10-15°F. cooler than at the base of the mountains. Precipitation is 50% greater in the spruce and fir habitat than at the foot of the hills. Such a cool, superhumid climate is approached at sea level in northern New England and adjacent Canadian provinces and in the coastal region of the Pacific Northwest. In the high-elevation forests of the South, vegetation similar to that of the Adirondack boreal woods of New York and the Maine coasts occurs. However, southern-grown spruce and fir trees grow faster and taller than those of the northern woods.13
Soils—The rocks and minerals of the Blue Ridge are primarily metamorphic, with gneiss, schist, quartzite, and slate particularly common. In the southern reaches, accumulations of sediments have formed siltstone, sandstone, and conglomerates. The soil derived from these rocks varies with the kinds of mineral formations and with the direction and degree of slope. Except on the steepest mountain sides, the acidic soils are shallow, sandy, and contain much organic matter. Nutrient levels vary greatly. The usually permeable subsoils are well-drained.
In the southern sector of the Blue Ridge province, a transition from gray-brown podzolic to red-yellow podzolic soils takes place. The fine-textured soils, whether derived from sandstone or from shale parent materials, produce crusts on the surface following rains and drying winds. This impervious layer prevents seedling emergence and reduces the infiltration of precipitation.
The lay of the land affects site quality and the occurrence of certain vegetation because of the angle at which the soil surface intercepts the sun's rays. South-facing slopes steeper than 10° intercept appreciable solar radiation during part of the day; in the summer they get the sun's rays at nearly right angles, thus receiving appreciable heat. Rainwater evaporates more rapidly, fires are more frequent, tree growth is retarded, and the more-xeric species prevail on these drier sites. As high soil temperature accelerates decomposition of organic matter, the lesser amount of decayed vegetable matter in the soil encourages erosion. This, in turn, results in shallower and less-fertile soils for tree growth. Western-facing slopes exposed to direct sunlight in the afternoon, when the air is warmer, are similarly affected. They are drier than those facing east. Better sites generally occur in these mountains, as a generality, on slopes that face north and northeast.
Forests—Perhaps the richest variety of tree species in the world's temperate zones occurs in the Blue Ridge province. Prior to the introduction of the fungus disease Endothiaparasitica, American chestnut occurred here in pure stands on a variety of sites. Though most types at lower elevations are variations of the broad oak-hickory association, American basswood, white ash, and black cherry are also important deciduous trees.
While red spruce may occur with hardwoods at elevations as low as 3500 feet, this conifer transitions to pure stands or mixes with Fraser fir at higher elevations. The latter species is believed to be a relict population of a once-continuous fir type that included balsam fir, a tree now restricted to the northern region of North America.14
Oak and hickory forests cover about 70% of the Southern Appalachian provinces. Oak and pine mixtures and various conifers each cover another 10%. The pines include loblolly and shortleaf on a variety of sites, Virginia pine on cutover and burned sites, table-mountain pine at the highest elevations, and pitch pine on scalp locks, the summits of the hills.
Scalp locks describe the ridges where separate fires in the past have met as flames simultaneously raced up two or more sides of a mountain. Where such fires meet, explosions erupt from the heat of combustion, and whole trees are tossed like matchsticks into the air. Even though pitch pines die in the holocaust, the serotinous nature of the species enables its perpetuation—the tightly sealed cones open, heat having dissolved the resinous glue that seals shut their scales. After the fire has passed and the ground cools, the seeds from within the cones hanging in the tops of the now-dead trees flutter to the ground, soon to germinate in the seedbed of bare mineral soil.
Lesser species include eastern white pine and eastern hemlock, the latter invading stands of the former in ecological succession. White pine, a pioneer tree on cutover, burned-over, or cultivated lands and storm-damaged stands, seldom regenerates under its own canopy. Like all light-demanding species, white pine grows in even-aged stands.
Hemlock, however, a shade-tolerant conifer, germinates and endures well under the crowns of the pines as well as under its own canopy. In time, hemlock trees (or other shade-tolerant species) of all ages capture white pine sites. As the pines die out, the forest becomes essentially pure hemlock until fire, storm, or harvest begins anew the ecological cycle. Carolina hemlock, limited to mountain ranges, displays silvical characteristics similar to those of eastern hemlock.
In the Great Smoky Mountains, 15 important vegetation types are recognized, their occurrence depending principally on elevation and moisture availability. Deciduous forests predominate below
4500 feet, while spruce, fir, and treeless balds covered with heather are the main vegetative types above that elevation. Virginia pine is the principal conifer at elevations below 2200 feet, pitch pine from there to 3200 feet, and table-mountain pine above that zone until the spruce-fir type of the ridge is reached. While soils and aspect play a role, along with climate, in delegating certain species to certain sites, the physiographic and edaphic roles are perhaps greater in the fertile coves of alluvium where American beech, yellow-poplar, Ohio buckeye, American basswood, and several birches make up much of the deciduous stand. There, eastern hemlock also encroaches to eventually claim its climax position.
Much of the existing forests of the mountainous South are at the higher elevations where stony soils formed from less-fertile sandstone and shale are of little value for farming. Here, various combinations of pines, oaks, hickories, yellow-poplar, and hemlock prevail. The absence of acid-loving mountain laurel, rhododendron, and wild azalea indicate ridges capped by dolomite, a form of limestone coated with magnesium.
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