Climatic Regions of the United States, Humid Subtropical
This climate region, characterized by long, hot, sultry summers, is found in the southeastern United States. North Carolina, South Carolina, Georgia, Alabama, Mississippi, Louisiana, Florida, and portions of surrounding states are included. In some areas, the growing season lasts for eight months or more.
Temperatures average 26° C (80° F) in the summer and range from 4° C to 10° C (40° F to 50° F) in the winter. The Humid Subtropical climate receives ample precipitation, averaging about 760 mm (30 in) annually in the western part of the region to more than 1,500 mm (60 in) per year in the southern part. Most precipitation occurs in the summer months as rainfall. A polar air mass can push southward and bring an infrequent snowstorm, but snow seldom stays on the ground for more than a few days.
Ultisols are the dominant soil type of this climatic region. This red soil is less fertile because abundant summer rainfall leaches mineral nutrients from the topsoil. Without fertilizers, these soils can support crops for only two or three years before nutrients are exhausted. The use of fertilizer extends land use in this climatic region.
The natural vegetation in the Humid Subtropical climate zone is the subtropical evergreen forest. This forest occurs in two forms: broadleaf and needle-leaf. The subtropical broadleaf evergreen forest often has a well-developed lower layer of vegetation, including ferns, small palms, shrubs, and herbaceous plants. The subtropical needle-leaf evergreen forest of the southeastern United States is known as the southern pine forest. Loblolly and slash pines dominate the uplands. Bald cypress grows in the swamps of this area. Timber companies have created many plantations in the area yielding valuable lumber and pulp.
The long growing season, ample precipitation, and the substantial use of fertilizers and other additives necessary for high, sustained crop yields makes this region an important agricultural area. Rapid tree growth supports the pulp, plywood, and lumbering industries. Specialty crops such as tobacco, cotton, sugarcane, citrus fruits, and rice are also grown.