Longleaf Pine24

Usually found on sandy lands and often accompanied by turkey oak and other scrub hardwoods, longleaf pines also seed-in on moist sites subjected to drought where the soil has been exposed. Fire exposes the mineral soil as flames consume pine straw lying on the forest floor. Pure stands give way to mixtures with loblolly, slash, and shortleaf pines in loamy flatwoods and along the streams of the lower Coastal Plain. Longleaf pines grow on clay as well as sandy lands, regardless of fertility. Along the Atlantic coast, the species' occurrence on sites where water occasionally perches over shallow surface soils atop impervious subsoils probably influenced the taxonomist Linnaeus in naming the species palustris, meaning swamp.

A fire-subclimax type, this species dominates the forest only if periodic fires occur. Prior to the Europeans' entry into these woods, dead snags were often struck by lightning, setting the grassy lands on fire. With fire exclusion in recent years, the acreage covered by this species has greatly diminished. New natural growth is likely to be slash pine along the eastern Gulf and Atlantic coasts and loblolly pine in the western sector of the Gulf coastal area.

Acreage decline also is attributed to the clear-felling of vast expanses without leaving a single seed-producing longleaf pine tree in the days of the cut-out-and-get-out lumbermen, to hogs' grazing on seedling roots rich in carbohydrate, and to a seedling blight. Other causes for the species' reduced range include cone- and seed-insect infestations, heavy (though winged) seeds that do not travel far with the wind, a ground cover of grass and forbs (called rough) through which the seeds do not penetrate to reach mineral soil for germination (unless fire passes through to reduce the amount of rough), and consumption of the seeds by rodents and birds. While more than 100,000 seeds per acre might fall within a stand adjacent to an opening, only 15,000 fall within 130 feet of a forest's edge, and few sail with the wind beyond that rim into a clearing. However, with especially abundant (although rare) seed crops, adequate numbers fall in clear-cut openings as far as 500 feet from walls of trees.

Longleaf pine seeds germinate shortly after seedfall in the autumn. This enables initial establishment of seedlings in the sandy, often droughty, soils. A long taproot then penetrates lower-level soil horizons, absorbing moisture and nutrients during the winter, spring, and early summer. Thus, the seedling is well established before late summer droughts occur. In contrast, all other southern pine seeds overwinter on the cold, moist ground, germinating in the spring. (Abnormally cold spells in late winter, however, can readily kill the freshly germinated longleaf pine seedlings by frost-heaving them from the ground.)

Competing vegetation underlying longleaf pine-turkey oak forests in Florida's sandhills includes explosively dispersing seed plants including bullnettle, rattlebox, and queen's delight. Ballistically, dispersed seeds are distributed from a "maternal patch" of about a meter in diameter. Harvester ants then carry the seeds as far as another 8 meters. Without the insect's aid, dispersal alone would not be adequate for moving the seeds beyond the maternal patch to establish a new colony to compete with the pines for soil moisture and nutrients.25

Figure 2.14 Note the flat top in this fine longleaf pine stem, evidenced by cessation of height growth and maturity for that particular site. Diameter growth continues. (USDA Forest Service photo by W. Matoon, 1930)

Nanism—Temporary nanism of longleaf pines keeps seedlings in the grass-stage. No other North American tree (except on occasion South Florida slash pine and pitch pine in the New Jersey barrens) demonstrates this dwarfing, a condition often solely and erroneously attributed to vegetative competition (including other longleaf pines) for moisture and nutrients. Nanism is at least partially an inherited seedling trait under rigid genetic control, although the length of time in the grass-stage—from 2 to more than 25 years—is strongly influenced by plant competition and the environment. The short shoot habit may be associated with the production of auxins—naturally occurring plant-growth hormones—in newly germinated seedling buds during early stages of development. The popular belief that seedlings, appearing like clumps of bunch grass, remain in the grass stage until taproots reach moisture seems unfounded. Taproots grow to depths of more than 6 inches in three months and twice that distance in the first 5 months after seed germination. Meanwhile, lateral roots develop, enabling absorption of moisture even from droughty surface soils.

As a rule of thumb, seedlings remain in the grass stage until they reach 1 inch in diameter at the root collar, then, almost invariably, emerging from the grass. In the earliest grass stage, the terminal meristem, out of which the needle fascicles arise, forms a flat surface. Then, a slight convex curvature develops in this fascicle-bearing organ, and a semblance of a bud appears. The typical silvery white pointed bud eventually develops into a main axis from which lateral fascicles arise. Once the conical bud has appeared, elongation occurs rapidly and dominance is strongly expressed. Annual height growth for the tree may then exceed several feet for a few years. The saplings appear so similar to some grasses that oldtimers from the days of the Civilian Conservation Corps, decades after their planting experiences, realized that they had planted nursery-grown stock among naturally regenerated seedlings in 1938. The trees more recently appeared random, not in rows as planted stock would be. Alas, the nursery-supplied seedlings had died.

Figure 2.15 Three-year-old longleaf pine seedlings in the grass stage. The tree on the left had been released from the scrub oak competition; the one on the right had not.

Pocket gophers, soil burrowing vegetarian rodents appearing like stout mice but with strong claws for digging, play havoc with grass-stage seedling stands in sandy soils. Making extensive tunnels about four inches in diameter in their search for starch and the resinous flavor of pine roots, the mammals sever the roots below the ground. Gophers dig rapidly, their obvious entry mounds leading to tunnels. After a summer rain, they "throw out" perhaps two mounds a day. One family threw out over 300 mounds on l0 acres in a single year. Usually meadow dwellers, preferring bitter dandelion roots to those of pines, pocket gophers migrate out of young forests when tree crowns close. They not only cut roots in constructing tunnels, they also eat the roots. Perhaps apocryphal is the tale that one can witness seedlings disappearing as they are pulled by the rodents into their tunnels below the surface of the ground. Cottontail rabbits also destroy seedlings by nipping off terminal shoots for food and moisture.

Fire—Longleaf pine seedlings resist most fire injury after their first year and until height growth begins. In the grass stage, the single large bud on each seedling is shielded from the heat by a sheath of needles. Bud protection by the rosette of foliage is demonstrated by letting a fire sweep over a stand of seedlings in which buds have been wrapped with cigarette papers. Needles will burn to 1-inch stubs, with the papers left unscorched. Once the seedlings emerge from the grass to make initial height growth, trees may be injured by fire—heat from the burning rough rises to kill buds, because the thin bark on the young stems is an inadequate insulation against high temperature.

Fire has little, or no, measurable effect on the soil and the roots of trees in it. If roots are injured, new feeders develop in the top few inches of soil. Occasional fires, temporarily increasing

Figure 2.16 A longleaf pine forest floor. Burrows made in the surface soil were probably tunneled by pocket gophers, mammals of the genus Geomys. A note on the 1936 photo indicated the site had not been burned for at least 30 years, an unusual situation for sites supporting this species. (USDA Forest Service photo)

Figure 2.16 A longleaf pine forest floor. Burrows made in the surface soil were probably tunneled by pocket gophers, mammals of the genus Geomys. A note on the 1936 photo indicated the site had not been burned for at least 30 years, an unusual situation for sites supporting this species. (USDA Forest Service photo)

nitrogen and exchangeable cations, may be slightly beneficial in the typically acidic soils in which the species grows. Calcium, potassium, and other positively charged ions released in the ashes of the oxidized organic matter become available to the trees, and to other plants.

Where soil organic matter is not appreciably altered by fire, bacterial populations proliferate. These microbes, however, hasten decay of vegetative organic matter and, in the process, consume a significant amount of nitrogen. To the detriment of higher plants, some soil nitrogen may be liberated to the atmosphere by the heat of fire. Yet, at the same time, more nitrogen in the soil becomes available to plants.

Many more forms of microfauna are found in unburned ground cover of longleaf pine forests than in burned areas characterized by herbaceous cover and where fermentation and humus layers are absent. The surface 2 inches of unburned soils have many more mites, earthworms, ants, and crayfish than do burned sites. As for macrofauna, cotton rats move from burned to unburned fields while old-field mice and Florida deer mice remain to nest in areas scorched by fire.

In a longleaf pine site in which slash pines had been planted, prescribed burning at 3-year intervals, the earliest time at which fuel is sufficient, does not sustain greater yields of herbage for cattle. For herbage production, the use of fire may just as well begin when trees are 9 to 12 years old. Early burning does, however, maintain woody browse for wildlife.26

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