Slash pine: characteristics, history, status, and trends

-Slash pine is the premier tree species on many sites throughout the South. Its ease of establishment and early growth, however, has extended its range to many sites where its performance has been less than ideal. For that reason, the acreage and volume of slash pine are declining. Nonetheless, it will continue to be the favored species on many sites where it is the most appropriate and productive species. This paper reviews slash pine's important silvical characteristics, its history of use and management, and the status and trends of this important resource. INTRODUCTION Typical slash pine (Pinus elliottii Engelm. var. elliotti,) is an excellent timber tree and one of the most important pine species in the Southern United States. Many prefer it for its fast growth and excellent utility for fiber, lumber, poles, and gum naval stores. The habitat and preferred sites within its natural range include poorly drained flatwoods and stream edges, as well as seasonally flooded areas such as bays and swamps. The ease and success of planting slash pine have significantly increased in its range. ~xt insive planting and natural regeneration of open agricultural and forest land brought a sharp rise in slash pine acreage between 1952 and 1970 (Sheffield and others 1983). Much of the planting was on sites that did not favor slash pine, and where performance was less than optimal. As a result, land managers have planted either loblolly (P taeda L.) or longleaf (P palustris Mill.) after harvesting the slash pine. However, slash pine is an excellent species and should be favored on appropriate sites. This paper reviews the important silvical characteristics of slash pine; provides a history of its development, use, and management; reviews its status in southern forest ecosystems; and explores trends in managed slash pine forests. SlLVlCAL CHARACTERISTICS Identifying Characteristics The typical slash pine tree has a long, clear bole and a relatively short crown, which results from self-pruning. South Florida slash pine (P. elliottiivar. densa) (Little and Dorman 1954) differs from the more northern variety in a number of ways, primarily because its seedlings go through a dwarf "grass stage" similar to longleaf pine. Its stem divides into large, spreading branches that form a flat-topped or rounded crown. Its uniqueness and limited range have encouraged neither research nor management of south Florida slash pine. The needles and cones of the typical slash pine represent its primary identifying characteristics. Needles are 7 to 10 inches long in fascicles of two and three on the same tree. They are dark, glossy green, and tufted at the ends of tapering branches. They extend back some distance along the branch and persist until the end of the second season. Cones are 4 to 6 inches long, ovoid conic, and sessile (fig. 1). They usually remain on the tree until the second summer. Cones are reddish brown, lustrous, and armed with a sharp spine. The seeds are about one-fourth inch long, dark brown-black mottled, with thin, translucent wings about 1 inch long. Figure l ( A ) mature, 2-year, closed cone (3 to 6 inches long); (B) mature cone open after shedding seed; (C) tips of cone scale showing variation in form of apophysis and stout prickle; (D) ventral side of cone scale with seed in place (left), and dorsal side (right); (E) and (F) seed and wing detached; (G) seed and wing intact (Mohr 1 896). 'James P. Barnett, Chief Silviculturist; and Raymond M. Sheffield, Resource Analyst, U.S. Department of Agriculture Forest Service, Southern Research Station, Pineville, LA 71 360 and Asheville, NC 28804, respectively. Bamett, James P; Sheffield, Raymond M. 2004. Slash pine: characteristics, history, status and trends. In: Dickens, E.D.; Bamett, J.P.; Hubbard, W.G.; Jokela, E.L., eds. Slash Pine: still growing and growing! Proceedings of the slash pine symposium. Gen. Tech. Report SRS-76. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southem Research Station: 1-6 Phenology Seeds mature in a 3-year period from when the strobili are initiated. The primordia of new strobili are detectable in late spring. These cone initials overwinter as buds the first year. When pollen is shed in late January or February of the second year, the male strobili are purple and 2 inches long. The female strobili appear on stalks in the upper crown and are about 1 inch long and red to purple at the time of pollination. Soon after pollination, the pollen tube stops growing and appears to remain in a quiescent state for the summer and winter. During the third growing season fertilization occurs-some 12 to 14 months after pollination. Cones enlarge and seeds mature during the third summer. Needles develop on new growth in spring and persist until the end of the second growing season. Distribution The natural range of slash pine is the most restricted of all major southern pines, extending from southern South Carolina to central Florida and westward to southeastern Louisiana (fig. 2). Although its natural range is relatively small, slash pine has been planted widely and its range extended into eastern Texas, southern North Carolina, and the sandhills between the Coastal Plain and the Piedmont through much of the Southeast (Fisher 1983). Slash pine has been introduced into many countries for timber production. Large-scale introductions have occurred in Brazil, Chile, Argentina, Venezuela, China, South Africa, New Zealand, and Australia. In most of these countries, it is an adequate seed producer, and natural or artificial regeneration continues. SOILS AND PHYSIOGRAPHY Soils within the range of slash pine are mostly Spodosols, Ultisols, and Entisols. It is generally believed that prior to extensive fire suppression and planting programs, slash pine was restricted to ponds, pond margins, and Coastal Plain flatwoods where ample moisture provided some degree of protection for young trees that are often killed by fire (Gruschow 1952). Topography varies little throughout the southeastern Coastal Plain, but small changes in elevation often coincide with abrupt changes in soil and site conditions. Although slash pine adapts to a wide variety of conditions, it grows best on deep, well-aerated soils that supply ample moisture during the growing season. Generally, growth and site index increase with depth to a restrictive layer or seasonally high water table, if these features occur within 20 to 30 inches of the soil surface. Where depth to a restrictive layer exceeds about 30 inches, site index declines with increasing depth to a reliable source of moisture, such as a stable water table or a soil horizon with large moistureholding storage capacity. Soil properties useful in estimating site index of slash pine include depth to gray mottles, depth to a spodic horizon, depth to the least-permeable layer or to a fine-textured horizon, thickness of the A1 horizon, and texture of the least-permeable or finest textured horizon (Lohrey and Kossuth 1990, Shoulders and Parham 1983). SILVICULTURAL CHARACTERISTICS Slash pine is a subclimax species that without human intervention and in the absence of fire or other catastrophic event will proceed to a mixed hardwood forest. Some authors consider it intermediate in tolerance to shade, others consider it intolerant. It will reproduce naturally in small openings and invade poorly stocked longleaf pine stands, although competition from overstory and understory vegetation reduces growth and causes much mortality. The two varieties of slash pine differ in their patterns of growth. Typical slash pine makes excellent early height growth, but south Florida slash pine has a grasslike, almost stemless stage that lasts from 2 to 6 years. Moreover, south Florida slash pine lacks the straight axis or stem characteristic of the typical variety and often develops forked boles with large branches and an open, spreading, irregularly shaped crown (Little and Dorman 1954). Figure 2-The current distribution of slash pine. Typical slash pine is slow to express dominance in dense, even-aged stands. As a result, height growth is slower in very dense stands than in moderately or lightly stocked stands. Young stands respond promptly to thinning or