Sand Pine

Sand pine is native to the deep, coarse-textured soils of relatively high, dry ridges in Florida and Alabama. It frequently occurs in dense, even-aged, pure stands of relatively minor importance and is associated with scrub oaks, scrub hickory, and dune holly. Past fires influence the prevalence of the species, which is rather tolerant to shade in youth, becoming less so with age. Stems express little dominance over their neighbors in the stand, whether of the same species or another.

Sand pine flowering extends from late December to late January. As for other southern pines, conelets grow little the first year, develop rapidly in the spring of the second year, and mature in late summer. The trees do not produce heavy seed crops every year. The size of the crop and the number of seeds in the cones are greater when precipitation during the period that flowers are formed than in contrast to drought years.

Cones, produced as early as age 5, may—because of the serotinous nature of the species—be held for many years before releasing their seeds. Seeds from recently matured cones are most viable between mid-September and mid-November, viability dropping rapidly over a 5-year period during which cones are retained. Following fire, most viable seeds will be released within a week. Germination occurs in winter, 2 to 3 months after seeds fall. After 3 months in the soil, many seeds are no longer viable.

Adequate moisture and warm temperature in winter result in germination in 2 weeks, making young seedlings susceptible to frost damage. Damping-off, root rot fungi, and nematodes also injure freshly germinated stock. Harvester ants consume seeds, even when no more than two nest hills occur per acre. White-footed deer mice, centipedes, mourning doves, and chewinks also eat great quantities.

Two races—Sand pine occurs as two races: Choctawhatchee and Ocala, named for distantly separated Florida national forests in which each race predominates. The former Choctawhatchee National Forest (now Eglin Air Force Base) lies in the West Florida Sandhills, while the Ocala National Forest is in the upper central zone of the peninsula.

Cones of the Choctawhatchee race release seeds every autumn, in contrast to the serotinous nature of the Ocala stock, which usually holds seeds until high temperatures are generated by fire or the sun's reflection on the light-colored sands in open stands. Seeds of the Ocala race in cones on trees along stand borders and roads often are released without subjection of the cones to heat other than that from the sun in the opening. The sporadic nature of Choctawhatchee seed release often results in sparse, uneven-aged stands. This encourages intrusion of scrub oaks.

Heat intolerance actually may be a cause of poor seedling survival. This was shown when roots were bathed with hot water at a temperature of 120°F for nematode control. The roots died. Yet, surface soil temperatures of 160°F frequently occur in sand pine sites. Soil temperatures of 116°F do not visibly injure trees.

Maximum photosynthesis takes place at about 78°F, becoming negligible at temperatures above 140°F. On the other hand, the relative efficiency of sand pine in carrying on photosynthesis at high

Figure 2.21 Longleaf pine seedlings, if not protected by hog-proof fencing, may be pulled from the ground by piney-woods rooters. A single tusked boar has been known to consume the roots of 80 trees in an hour. (USDA Forest Service photo by J. Cassady)

temperatures may account for successful plantation establishment on hot sands where other conifers fail. Temperatures are notably cooler just under bare sand within an unshaded litter layer or the upper 1/2 inch of a charred surface soil than on the surface of the ground.34

The Big Scrub—The Big Scrub of central peninsular Florida, in which sand pine is the dominant species, is apparently the result of the inability of coarse sands to store water for more than a few days. These unconsolidated sands were moved from the Appalachian Mountains and the Piedmont of the Carolinas and Georgia during the Pleistocene period, transported to the Florida peninsula by offshore currents, washed and sorted, and finally exposed upon the lowering of ocean waters in the Big Scrub.35

A relatively pure stand of sand pine of over 200,000 acres occurred before recent engineering developments in this gigantic, flattened pine-clad dune. Intermixed with sand pine to a slight degree and on adjacent hammocks or "islands" with better soils of greater moisture-holding capacity are longleaf, slash, loblolly, and pond pines. The presence of the associated species, especially longleaf pine, may relate to wildfire occurrence, burning in turn varying with the physiography of the site and with quantity and kind of fuel to feed the flames. While longleaf pine stands on the slightly elevated ridges have a ground cover of wiregrass and other flash fuels, the longleaf pine withstands fire much better than do forests of sand pine.

Species transition in the Big Scrub is so obvious that roads are laid out to conveniently separate the timber types. Deep, white, coarse sand may support sand pine on one side of a lane, while slightly more fertile yellowish, finer sand produces longleaf pine on the other.

Figure 2.22 Left unchecked by fire, scrub oak vegetation captures sand pine sites. Fire, prescribed or wild, enables control of the broadleaf weed trees and the release of seeds from the cones. Sites like this in the Big Scrub have also been burned in order to establish more valuable species, like slash and longleaf pines. (USDA Forest Service photo by E. Hebb, 1957)

Figure 2.22 Left unchecked by fire, scrub oak vegetation captures sand pine sites. Fire, prescribed or wild, enables control of the broadleaf weed trees and the release of seeds from the cones. Sites like this in the Big Scrub have also been burned in order to establish more valuable species, like slash and longleaf pines. (USDA Forest Service photo by E. Hebb, 1957)

Where sand pines intermix with longleaf pines, cones of the former appear to open more readily, leading to the observation that the serotinous characteristic may relate to soil fertility, trees on the less fertile typical sand pine sites exhibiting the seral nature.

Evergreen scrub oaks (myrtle, Chapman, and sand live) follow sand pines in ecological succession in some sites—like hammocks—from which fire has been excluded. Species other than sand pine make satisfactory growth where moisture is adequate in this bed of silica, to which the term "soil" is but remotely applicable. Physical and chemical properties of the soil, aside from those associated with texture, are not notably better than for the more favorable peninsular sites supporting more-demanding trees. As silt plus clay content (up to 8 percent) at pond borders increases, the amounts of potassium, calcium, magnesium, and phosphorus also increase.36

Soil water may not be chiefly responsible for the type occurrence; distinction in vegetation may be attributed to an as yet unknown nutritional deficiency in these severely leached soils. No grass grows here: Rosemary and poor joe are the principal shrub and forb. A mat of lichens covers the ground. Even animals, micro and macro, avoid the area, for the sands reflect the glare of the burning sun to take a toll of the unfit.

Probably no ecological successional invasion of vegetation in the Big Scrub occurs from the adjacent sandhills in which wiregrass and sawpalmetto accompany longleaf pine and turkey oak. The plants of both communities seem to have remained static for millennia, seldom mixing. Where species transition gradually occurs, it is because either (1) severely washed and sorted sands were air-lifted to intersperse with less-strongly washed and sorted deposits or (2) insufficient washing and sorting took place to limit an area to the only tree species capable of withstanding extremely xeric conditions.37 Contrarily, sand pine invades longleaf pine islands and ridges with which it borders. Sand pine even encroaches in slash pine and loblolly pine stands of the wet flatwoods.

Figure 2.23 A well protected sand pine tree of unusually good form. With heat to open its cones, the seeds from a single tree like this specimen could seed-in an acre. (USDA Forest Service photo by W.D. Brush, 1950)

Scrub plants in the sandhills may leach allelopaths. These organic chemicals could keep the soil bare of competing herbaceous plants and pines that provide fuel for surface fires that otherwise cause shrub mortality. This may account for the abrupt transition from sand pine scrub, with its dense understory of evergreen oaks and minimal ground cover, to sandhills of open woodland dominated by longleaf and slash pines and deciduous oaks. Under these latter trees, in contrast, grow mats of native grasses.38

Sand pine site indexes in the Big Scrub range from 50 to 70. However, as the species matures in 35 years, trees seldom reach the 50-year height by which site index is defined. Some consider the denser wood of the Choctawhatchee race ideally suited for biomass production in energy plantations.39

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