A number of species are included in the group marketed as Southern Pine lumber. The four major Southern Pine species and their growth ranges are as follows: (a) longleaf pine (Pinus palustris), eastern North Carolina southward into Florida and westward into eastern Texas; (b) shortleaf pine (P. echinata), southeastern New York and New Jersey southward to northern Florida and westward into eastern Texas and Oklahoma; (c) loblolly pine (P. taeda), Maryland southward through the Atlantic Coastal Plain and Piedmont Plateau into Florida and westward into eastern Texas; (d) slash pine (P. elliottii), Florida and southern South Carolina, Georgia, Alabama, Mississippi, and Louisiana east of he Mississippi River. Lumber from these four species is classified as Southern Pine by the grading standards of the industry. These standards also classify lumber produced from the longleaf and slash pine species as longleaf pine if the lumber conforms to the growth-ring and latewood requirements of such standards. Southern Pine lumber is produced principally in the Southern and South Atlantic States. Georgia, Alabama, North Carolina, Arkansas, and Louisiana lead in Southern Pine lumber production.  The wood of these southern pines is quite similar in appearance. Sapwood is yellowish white and heartwood, reddish brown. The sapwood is usually wide in second-growth stands. The heartwood begins to form when the tree is about 20 years old. In old, slow-growth trees, sapwood may be only 2 to 5 cm (1 to 2 in.) wide.  Longleaf and slash pine are classified as heavy, strong, stiff, hard, and moderately high in shock resistance. Shortleaf and loblolly pine are usually somewhat lighter in weight than is longleaf. All the southern pines have moderately high shrinkage but are dimensionally stable when properly dried.  To obtain heavy, strong wood of the southern pines for structural purposes, a density rule has been written that specifies a certain percentage of latewood and growth rates for structural timbers.  The denser and higher strength southern pines are extensively used in the form of stringers in construction of factories, warehouses, bridges, trestles, and docks, and also for roof trusses, beams, posts, joists, and piles. Lumber of lower density and strength is also used for building material, such as interior woodwork, sheathing, and subflooring, as well as boxes, pallets, and crates. Southern Pine is used also for tight and slack cooperage. When used for railroad crossties, piles, poles, mine timbers, and exterior decking, it is usually treated with preservatives. The manufacture of structural-grade plywood from Southern Pine is a major wood-using industry, as is the production of preservative-treated lumber.