Species Overview

Ten hard, or yellow, pines occur in the southern United States. The four species most important commercially are shortleaf, loblolly, longleaf, and slash pines. In this order, their ranges generally occur from north to south within the region. Other yellow pines of the South are Virginia, pitch, pond, sand, spruce, and table-mountain. (Eastern white pine, confined in the South mostly to the Appalachian Mountains, is a soft pine. For that and other botanical reasons it is not classified as a southern pine. It is listed with the lesser conifers in Chapter 3.)

Shortleaf pine, the most cold hardy of the four principal species, intermixes with loblolly pine throughout much of its range. As a rule, shortleaf pine predominates to the north of an imaginary line across the middle latitude of the Gulf Coastal Plain, while loblolly pine is the more abundant of the two species to the south. Throughout much of the Ouachita Mountains of Arkansas, shortleaf was the only pine until the introduction, beginning in the 1950s, of loblolly pine on industrial and government lands.

Loblolly pines, the tall trees first encountered by the early pioneers as they stepped ashore in the murky loblollies along the southern Atlantic Coast, are the most important timber-producing

Figure 2.1 Hardwood encroachment in pine stands. A mixture of perhaps 50 broadleaf species enters the stand in the absence of fire. Controlling weed trees in order to encourage growth of the more valuable pines is a continuing task for the forester. (USDA Forest Service photo).

trees of the southern forest. Often most vigorous at the edges of swamps, the species prefers wetter sites, attaining maximum growth on poorly drained clay and clay loam soils. The name derives from the early-English term for a mudhole and the color of the broth called loblolly served as rations for the sailors on the vessels that landed on Virginia's coast. However, loblolly pine also grows in pure stands on drier sites in a zone of Central Texas.

Longleaf pine, although given the Latin species name palustris—meaning in the ancient language "swamp"—is usually a dry-site tree.1 Typically found in dry sands of the lower Gulf Coastal

Figure 2.2 The result of natural and human influences on loblolly pine and shortleaf pine forests. Nature tends toward climax hardwood types. Pines are harvested in preference to hardwoods, and this hastens nature's swing toward broadleaf woodlands. (USDA Forest Service drawing by W. G. Wahlenberg)

Plain and the Fall Line sandhills of the Carolinas, the tree extends northward from the Gulf Coastal Plain as a finger into the shallow cherty soils in the mountains of northeastern Alabama.

Occasionally, longleaf and loblolly pines hybridize, giving rise to Sonderegger pine. This species cross appears like longleaf pine except for the lack of a grass-stage, called nanism, the classic dwarfing of the seedling stage.

Slash pine, often occurring in both natural and planted stands where virgin longleaf pines once covered the land, also hugs the lower Coastal Plain. Least cold hardy of the four primary southern

Figure 2.3 A 45-year-old stand of loblolly and shortleaf pines in the Atlantic Coastal Plain on Site Index 70 land. Note the encroaching broadleaf understory. Note, too, past ice-storm damage, evidenced by the crooks at about the same height in several stems, where tops had been broken or bent in a particular year sometime in the past. (authors' collection)

Figure 2.3 A 45-year-old stand of loblolly and shortleaf pines in the Atlantic Coastal Plain on Site Index 70 land. Note the encroaching broadleaf understory. Note, too, past ice-storm damage, evidenced by the crooks at about the same height in several stems, where tops had been broken or bent in a particular year sometime in the past. (authors' collection)

pines, trees are frequently broken by the heavy ice that accumulates on their branches when the species is planted north of its natural range. Until annosus root rot began to take its toll of planted trees in the 1950s, this was the most widely planted of the southern pines. Strobili phenology—the timing of pollen dissemination—usually precludes hybridization of slash pine with other pines.

Into the 1950s, slash pine, from Florida to eastern Louisiana, was cataloged as Pinus caribeae, along with similarly appearing trees of the Caribbean islands, the Bahamas, and Central America. Mainland North American trees were subsequently renamed P. elliottii to honor a botanist, leaving the original designation for the more southerly Central American (including Mexico) and island species.

Still later, dendrologists distinguished between the slash pines of northern and southern Florida. Those to the north in the peninsula and throughout the species' range to the west retained the species typical designation; those in the south of Florida became variety densa because of the harder wood. The needles are also longer. Another distinguishing characteristic for South Florida slash pine is the grass stage through which its seedlings often pass. Occasional harvests and conversion of forested tracts to agriculture have diminished the acreage covered by variety densa.

Virginia pine, pitch pine, pond pine, sand pine, spruce pine, and table-mountain pine, while not greatly significant commercially, are ecologically important species in the forests of the South. Peculiar characteristics, respectively, of the habitats of these hard southern yellow pines are dry sterile sites at sea level, moist ridge tops at 4000 feet elevation, organic swamps along the coast, inland plateaus with a distinctive fire history, and as an intermingler at the transition zone of more important timber types. When they occur in such odd locales, we call them "conifers of convenience."

Virginia pine, a scrubby tree, serves as a pioneer in ecological succession. Although not serotinous, it seeds-in abundantly from bumper seed crops following land disturbance or vegetation manipulation.2 The species also sprouts from epicormic buds at the root collar or just below ground level on a horizontal section of the root. Its prolific production of viable seeds and its sprouting habit encourage regeneration of this short-needled, short-boled, and small-coned tree on road cuts and burned-over, cutover, storm-damaged, and agriculturally abandoned lands in the southern Piedmont province and in the Appalachian Mountains.

Pitch pine, frequently found on the scalp locks of tree vegetation in the upper reaches of the Appalachian Mountains, is a serotinous species. It occurs on those ridges, as on other sites, because of past fires that heated the cones, thereby melting the resin that sealed the scales, of parent stems. Opened cones then release their winged seeds to flutter and fly to the ground.

Figure 2.4 Blue-stain infected wood. The fungus shows in all southern pine logs not immediately salvaged or milled (unless stored in a millpond or subjected to continuous hosing with water) following death or harvest. Beetle-infested trees are especially vulnerable to the lumber defect, one that, however, does not affect strength properties. (Texas Forest Service photo by R. Billings)

Figure 2.4 Blue-stain infected wood. The fungus shows in all southern pine logs not immediately salvaged or milled (unless stored in a millpond or subjected to continuous hosing with water) following death or harvest. Beetle-infested trees are especially vulnerable to the lumber defect, one that, however, does not affect strength properties. (Texas Forest Service photo by R. Billings)

Pond pine, for many years considered the same species as the mountainous pitch pine, is now classified separately. Its principal habitat is the other extreme in topography. Pond pines occur in pocosins and other swampy lands of the Carolina coasts. The species occasionally is found also in wet lands along the Gulf shore. Its serotinous nature enables its perpetuation on organic soils which, when dried to tinderlike conditions, are readily ignited. A fiery holocaust results. Shortly, after the fire has passed and the ground has cooled, the newly opened cones release seeds to restock the land with trees. Sprouts also arise from old stumps.

Sand pine is native to peninsular Florida and to a zone of the panhandle of that State and South Alabama. Only the strain that grows in the peninsula is serotinous. There, the reflected heat from the sun's rays on the white sandy soil is adequate for releasing seeds held in cones attached to logging slash that lies on the ground. The western race of sand pine is, for reasons unknown, not dependent upon heat for releasing its seed. As the seeds fall shortly after the cones mature and few seeds germinate in the unburned and therefore unprepared site, stands of trees in western Florida are less dense than those of the eastern race of the species.3

Spruce pine displays both bark and needles that resemble members of the Picea genus; yet it is a pine. The smooth gray bark and the foliage at first glance also sometimes appear like that of white pine. Locally it sometimes bears the name cedar pine. One finds spruce pine on damper soils surrounding dry islands of longleaf pine, particularly in southern Alabama, Mississippi, and Louisiana not far inland from coastal shores and just above the alluvium of river sides. A separate colony occurs in the Santee River zone of South Carolina's coast.

Table-mountain pine, found at high elevations in the Appalachian chain, is not a tree for the lumbermen. Little commercial use is made of the poorly formed, short, limby logs, although years ago it was reported to occur occasionally in pure stands suitable for timber production. The species' highest use is for watershed protection.

Flowers and Seeds

There is a chronological sequence for strobili (the "flowers" of conifers) production of the southern yellow pines. For the principal species, the phenological order of development coincides roughly with the natural ranges of the four principal species—from the warmer south to the cooler north within the region. In southern Mississippi, where slash, longleaf, loblolly, and shortleaf pines grow naturally in the same stand, pollen dissemination occurs, respectively, in early February, mid-February, late February to early March, and late March. Of course there is some overlap, causing natural hybridization as the sperm organs of one species fall on and fertilize receptive ovules of another. Pollen maturity may vary by as much as three weeks from one year to another and about three weeks between trees of the same species in the same stand. In Florida, for example, a spread of three weeks may occur for flowering of slash pines within a 15-mile radius and as much as two weeks for stands 3 miles apart.

Exceptionally cold weather during flowering causes female strobili to mature slowly, thus male organs may shed pollen before the females are receptive. Two crops of female conelets might develop as a result of unseasonably cold weather that kills the first strobili produced. The conelets likely will not mature if too few ovules within them are fertilized by the disseminated pollen. Sexual fertilization, the union of male and female gametes within the female cones, probably takes place when cones reach full size during the summer of the second year after flowering. Seed growth within the cone is then rapid.

Genetics probably controls the age of trees when flowers form. Trees of loblolly pine have produced seed-yielding cones at 4 years of age. That means flowering had occurred two years earlier. The yield of seed from a single cone is likely also an inherited characteristic, for yields (and seed weight) differ among the cones produced by individual parents of this species.

Hybridization—crossing between species—has created individuals of small size as well as those that exhibit the classical hybrid vigor. Hybrids may be adapted to a wider range of environ-

Figure 2.5 Conelets of a southern pine. Female strobili appear like these in mid-summer of the first year prior to pollination the following spring. Cones ripen in the fall, and seeds (except for longleaf pine) are released the following spring. (USDA Forest Service photo)

mental conditions than either parent. Crosses of loblolly and shortleaf pines resist fusiform rust to a greater degree than does loblolly pine alone, while longleaf pine crossed with slash pine makes height growth like that of the latter species, the seedling never passing through a grass stage. Nor does the loblolly pine and longleaf pine hybrid (P sondereggeri) exhibit nanism. Pitch pine crossed with loblolly pine outgrows, and has better form than, genetically pure pitch pine. This hybrid is more cold resistant than loblolly pine, surviving harsh climate and infertile soil better than does either parent. The cross also produces a more extensive root system and has better seedling survival than either parent. Crosses of loblolly and slash pines are thought to be more drought resistant than either parent.4

Flowering and, therefore, pollen production of the southern pines relate to accumulated temperature. Differences in heat requirements among the species probably account for purity of race, precluding overlapping pollination periods. Thus, temperature gradients in the days or weeks before flowering, when cool weather slows and warm weather hastens development and dispersal of yellowish-orange pollen from male strobili, at least partially controls hybridization.

Peak flowering of the southern pines may extend from three to six weeks, depending on the species. The production of Sonderegger pine can be attributed to the overlapping pollen shedding by the parent species in contrast to the lack of overlap for other species.5

Artificial hybridization of pitch pine and pond pine in seed orchards should not be considered extraordinary, even when the several-hundred-mile distance between the usual natural ranges for the species is considered. For a long time, as noted earlier, foresters cataloged both trees as Pinus rigida, the name derived from the stiffness of the foliage.

The ease with which loblolly pine and pond pine can be artificially hybridized, the greater cold-hardiness of pitch pine, and the better quality of loblolly pine have suggested the development of a three-way hybrid for planting in the northern reaches of the southern forest. (Hybridization with shortleaf pine also occurs.) Such an artificially developed hybrid could be as well received for lumber and plywood manufacture as loblolly pine.

Pine strobili and cones receive a lot of natural abuse. Thrips, an insect, injures flowers, causing them to shrivel and die. The insect also damages newly formed conelets. Cones are attacked by a small beetle (Ernobius sp) and several pitch moths (Dioryctria sp.). Upon attack, cone and seed development is arrested, cones become malformed and, in a crook in the cone, sticky frass collects.

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