Physiography—The Piedmont province, the eastern foothills of the Appalachian Mountains, extends from north of the Potomac River south to Alabama. Narrow in the north—about 50 miles wide in Maryland, the region broadens to 125 miles in North Carolina, and then narrows to the south. Elevations range from 300 to 1200 feet above sea level. The Piedmont, from the Italian for "foot-of-the-mountains," is often referred to as a plateau, probably because the namesake Italian formation at the foot of the Alps is relatively table-like.
The Piedmont, however, was once worn away almost to a plain by erosion. Then uplifted, the region was subsequently dissected to produce the undulating character of the present landscape. Old, metamorphosed rocks such as marble and quartzite cover much of the area, tending to form upland. Perhaps 20% of the region is underlain by granite, this rock's resistance to erosion also tending to result in uplands and some striking formations. Thus, the North American Piedmont consists of rolling hills and isolated features. Most notable of these is Stone Mountain in Georgia, a huge regolith rather void of tree vegetation. Softer rocks occur along the eastern margin of the Piedmont, for example, the so-called Carolina Slate Belt, extending from southern Virginia to Georgia, is characterized by valleys at lower than prevailing elevations. In the Piedmont are many other unmetamorphosed and noncrystalline rocks similar to those of the Appalachian highlands that serve as parent material for the soil.
Soils—Soils of the Piedmont are mainly red-yellow podzolics, either of sandy loam or clay loam texture. They are acidic and fairly high in nutrients where not eroded.9 Soil thickness, even if
erosion has been minimal, varies greatly. It is thin where derived from horizontal beds of schist and thick where these mineral layers have been displaced vertically.
Few regions in the United States, and perhaps the world, have experienced such severe soil losses from erosion as has the Piedmont. Widespread clearing and continuous cultivation of row crops on sloping surfaces have left the zone depleted of its once fertile topsoil. This is aggravated by the porous surface layers that rest over heavy subsoils. Frequent and intense rainfall and little snow for protection of the soil during winter storms further encourages erosion.
Because of erosion, one commonly sees exposed the reddish clayey subsoils that once underlay the rich loam surface horizons. This plastic material cannot absorb an inch of rainfall in 36 hours. The water runs off the surface, carrying the silt and clay sediments with it to the streams. Not only do these subsoils—now exposed at the surface—inadequately absorb water, they do not contain organic matter needed for improving the physical structure of the soil and, with it, tree vigor.
Every part of the Piedmont has lost 25% of its loamy surface horizon; much has lost three-fourths or more. The whole of the region, some have suggested, is now at least one foot lower in elevation than when the pioneers entered its mesic forests. As a result, much farm land has been abandoned and returned to forests.
Forests—Encroachment of undesirable hardwood trees is a major obstacle to forest management in this region. Frequent crops of wind-blown seed, exposed mineral soil for seedbeds, and full sunlight in openings combine to favor pine establishment on old fields. The shade-tolerant hardwoods become established in the understory within a few years.
Before the intrusion of European settlers into the southern Piedmont, a mixture of pines and hardwoods covered the land. Chestnut-oak-hickory or beech-birch-maple climax vegetation eventually replaced the pines that originated following fires or catastrophic storms. Pure pine stands occasionally were climax where soils are derived from sandstone or granite.
Sweetgum is an important invader in the Piedmont; providing high-quality veneer wood when growing on moist sites but a weed to be controlled on coarse, upland soils. Dogwood, once of significance for spindles in textile manufacturing, may take over large areas. This species is a soil-builder, its foliage laden with nutrients. Dogwood anthracnose disease threatens the range of this species.
About one-third of the Piedmont forest today is in loblolly pine and shortleaf pine types. This includes vast acreages of plantations. Oaks and hickories cover another one-third of the forested area; the oak-pine group about one-fifth; and the balance in oak-gum-cypress, Virginia pine, longleaf pine-slash pine, and elm-ash-cottonwood cover types.
Annual precipitation tallies 40 to 50 inches, about a third of which falls during the summer. Growing seasons vary from 180 to 210 days, depending principally upon latitude.
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