Nomenclature
A. System: Terrestrial (Allard 1990)
B. Physiognomic Type: Terrestrial woodlands
Classification System
This community refers to "longleaf pine-turkey oak (Pinus palustris - Quercus laevis) sandhills" of Stout and Marion (1993), "sandhill pine forests" of Christensen (1988), and "high-pine" of Myers (1990). Additional synonyms for this community are: sandhill country, xerophytic deciduous forest, xerophytic coniferous forest, pine-turkey oak sandridge, fall-line sandhill, Florida sandhill association, clayridge forest, dwarf oak forest, evergreen shrub forest, turkey oak barrens, scrub oak barrens, and sandhill pine forest (reviewed in Stout and Marion 1993).
Several longleaf pine-turkey oak sandhill communities are described under a variety of names in state classification systems. In Louisiana, there are several types of upland longleaf pine forests and sandy woodlands (Smith 1988). In Georgia, this community is called clayridge forest and dwarf oak forest (Wharton 1978). Nelson's (1986) xeric sandhill scrub and pine-scrub oak sandhill communities in South Carolina are types of this community, as are sandhills in Alabama (Currie 1989), pine-scrub oak sandhills, xeric sandhill scrubs, and coastal fringe sandhills in North Carolina (Schafale and Weakley 1990), and sandhills and upland pine forests in Florida (FNAI and FDNR 1990). In Virginia, the longleaf pine-turkey oak sandhill community is a type of oligotrophic or submesotrophic woodland (Allard 1990). In Texas, this community is part of the bluejack oak (Quercus incana) - pine series (Allard 1990).
Range
A. Bailey's Ecoregion: Province 232-Outer Coastal Plain Mixed Forest Province.
B. Current Distribution: Eastern Virginia south to Martin County, FL, and west along the outer coastal plain to the Big Thicket region of Texas. Interior stands occupy the fall line* in Alabama, Georgia, North Carolina, and South Carolina (Stout and Marion 1993).
Environmental Factors
A. Topographic Position: This community occurs in areas with rolling topography (Stout and Marion 1993). It occupies ridge tops, sand rims of Carolina bays, and relict dune ridges of lower coastal terraces (Christensen 1988). It also occurs on ridges of the fall-line sandhills, on the Southern Lake Wales Ridge of south central Florida, and on river terraces with deep sandy soils in the Big Thicket region in southeast Texas (Stout and Marion 1993).
B. Hydrology: The community generally occurs on well-drained, dry to xeric soils (Myers 1990).
C. Fire Regime: The natural fire return interval is believed to be every 1 to 3 years (Stout and Marion 1993). Compared to subxeric sandhills, the most xeric habitats may burn less frequently due to having a slower build-up of fuel. Frequent, low-intensity surface fires maintain this community (Christensen 1988).
D. Soil Features: This community occurs on both sandhills and clayhills. Sandhill soils are acidic, overly drained, highly permeable, low in nutrients, and are classified as entisols. In contrast, clayhill soils are characterized by clayey subsoil overlain by sand or clayey sand, and are classified as ultisols. Clayhill soils are well-drained. The clayey subsoil holds water that is available to plants. Fertility of clayhill soils ranges from good to moderate (Myers 1990).
Physiognomy/Structure
Community structure is characterized by an open, sparse canopy of pine, an open understory dominated by scrubby oaks (which are often stunted and gnarled) and a herbaceous ground layer consisting of various grasses and forbs (Myers 1990). Physiognomy varies with moisture, fire regime, and geographic location (see Variation in Structure and Composition, p 128).
Commonly Associated Plant Communities
This community may grade into pine flatwoods, sand pine (Pinus clausa ) scrub, mesic hardwood forest, xeric hammock (Abrahamson and Hartnett 1990) or a mixed oak-pine community (Harcombe et al. 1993). The soil, topographic, and disturbance factors that explain differences between this mixed oak-pine community and the longleaf pine community are not yet clear (Harcombe et al. 1993). Small, often isolated, examples of communities that may occur as inclusions in longleaf pine sandhills are sandstone outcrops (Smith 1988), sandhill seeps, small depression pocosin and ponds, and vernal pools (Schafale and Weakley 1990).
Reduced fire frequency may lead to an increase in stature of understory woody vegetation and a decrease in ground vegetation, followed by succession to a xeric hardwood/mixed pine community (Stout and Marion 1993). As a result of fire suppression over 40 years, the community may be invaded by scrub, mesic species, and sand pine as in Florida (Stout and Marion 1993). Invasion by these species may alter the fire regime from one characterized by short-interval, cool ground fires to one characterized by long-interval crown killing fires, which would maintain the community as a sand pine scrub community (Christensen 1988). Long-term fire suppression may lead to the development of a xeric hardwood forest (Christensen 1988; Stout and Marion 1993).
Biological Composition
A. Dominant Plant Species: Longleaf pine dominates the canopy except in southeast and south central Florida stands, which may consist of slash pine (Pinus elliottii) or a mixture of the two. In eastern Texas, longleaf pine, shortleaf pine (Pinus echinata), and loblolly pine (Pinus taeda) are codominants. Turkey oak dominatesthe understory in community occurrences east of the Mississippi River. Coastal fringe examples of this community have significant abundances of both sand live oak (Quercus geminata) and sand laurel oak (Q. hemisphaerica). Sandier inland sites will often include bluejack (Quercus incana) and sand post oak (Quercus margarettae) in addition to turkey oak. Post oak and blackjack oak are found on hills with more clay content. Persimmon is a very common understory species throughout the region east of the Mississippi River (Peet and Allard 1993). In the coastal plain west of the Mississippi, including the Big Thicket region of south eastern Texas, bluejack oak, sand post oak, and hickories (Carya spp.) replace turkey oak as understory dominants (Harcombe et al. 1993; Christensen 1988; Stout and Marion 1993). In Florida, wiregrass (Aristida stricta or A. beytrichiana) dominates the understory in community occurrences east of Escambia County. A transition in understory species dominance occurs in Escambia County with little bluestem and other bluestem grass dominating from there to east Texas (Myers 1990). On the western coastal plain, the drier longleaf pine woodlands have a sparse herbaceous layer, abundant lichens, and exposed sand. The important grasses include bluestems, dropseeds, and low panicums (Bridges and Orzell 1989).
B. Variation in Structure and Composition: Community composition and structure vary with fire frequency, soil, and geographic location. Christensen (1988) divided this community into three associations for the majority of the region east of the Mississippi River:
The association of pine-turkey oak sandridge forest occurs in the most xeric environments. Tree density is low (50/ha) and trees are stunted and gnarled. Turkey oak dominates the understory, and black gum (Nyssa sylvatica var. sylvatica) and persimmon (Diospyros virginiana) may occur as scattered individuals. The low shrubs, staggerbush (Lyonia mariana), and dwarf huckleberry form small clumps (2 percent cover). In addition, foliose lichens (Cladonia spp., Cladina spp.) and sand-binding lichen (Lecidea uliginosa) form a low mat. Broom moss (Dicramum spurium) dominates the ground under the oaks. Common and indicative herb species are sandwort (Arenaria caroliniana), tread softly (Cnidoscolus stimulosus), sand spikemoss (Selaginella arenicola), and wireplant (Stipulicida setacea; reviewed in Christensen 1988).
In the fall line sandhill association, ridgetops are dominated by turkey oak. Downslope, and with increasing clay content in the soil, blackjack oak, sandhill post oak, and bluejack oak share understory dominance. Other understory trees include blackgum, persimmon, and sweetgum (Liquidambar styraciflua). The ground cover is dominated by wiregrass, and also includes dwarf huckleberry and blueberry (Vaccinium spp.). In areas where vascular plant growth is sparse, mosses andlichens are abundant. Bracken fern (Pteridium aquilinum) becomes abundant in areas where the clay horizon is near the surface and moisture is abundant (reviewed in Christensen 1988).
In the Florida sandhill association, Monk (1968) recognized three phases: (1) driest sites were dominated by turkey oak, (2) finer textured, more fertile soils supported bluejack oak, and (3) calcareous soils were dominated by southern red oak. Longleaf pine may dominate the canopy or codominate with slash pine. The turkey oak phase is structurally similar to the pine-turkey oak sandridge association already described. The herb layer is dominated by wiregrass and slender dropseed (Sporobolus gracilis). Gopher apple (Chrysobalanus oblongifolius) is the dominant shrub, although it is also scarce. In the bluejack oak phase, live oak (Quercus virginiana) is a common canopy tree, and wiregrass forms a dense groundcover. The southern red oak phase grades into southern mixed hardwood forest (reviewed in Christensen 1988).
A second Florida sandhill association is the southern ridge sandhill community, which occurs in the southeast Lake Wales Ridge and is dominated by slash pine, or a mixture of slash and longleaf pines. Two understory phases are recognized: (1) turkey oak on well-drained sites and (2) scrub hickory (Carya floridana) at lower elevations on less well-drained sites (reviewed in Christensen 1988).
In the Big Thicket region of eastern Texas and in Louisiana, the canopy can be codominated by longleaf, shortleaf, and loblolly pines if fire is infrequent. The understory is codominated by bluejack and post oaks. Yaupon (Ilex vomitoria) and flowering dogwood also are common in the understory.
Exploitation of longleaf pine may have led to development of a community dominated by pines and oaks, rather than just pines. Historical accounts suggest that in precolonial times, ridges were dominated by longleaf pine, exhibited a relatively open understory, and experienced frequent fire. Pine extraction allowed turkey oak and persimmon to increase in dominance (reviewed in Stout and Marion 1993). Short-term fire suppression may lead to an increase in stature and abundance of understory trees and a decrease in abundance and richness of the ground cover (Stout and Marion 1993; see Successional Relationships, p 127).
* The fall line marks the separation between the Piedmont and Coastal Plain physiographic regions in the Southeastern United States.