West Gulf Coast Sandhill Oak and Pine Forest

This ecological system occurs west of the Mississippi River primarily outside the natural range of longleaf pine (Pinus palustris) and less commonly within this range. Like other sandhill systems of the Gulf and Atlantic coastal plains, this type is found on uplands underlain with deep, coarse sandy soils. These sites are typified by low fertility and moisture retention, which contribute to open tree canopies with usually less than 60% canopy closure. Sparse understory vegetation and abundant patches of bare soil are indicative of this system. Vegetation indicators are species tolerant of droughty sites, especially Quercus incana and Quercus arkansana, but also Quercus marilandica and Quercus stellata. Pinus echinata is usually present, and Pinus palustris is absent (or perhaps at low frequency within its range). This system supports a large concentration of vascular plant endemics, near endemics, and a number of plant species with high fidelity to sandhills in the region. Elsewhere in the Atlantic and Gulf coastal plains, including most of the adjacent outer West Gulf Coastal Plain ecoregion, these site conditions are closely associated with longleaf pine.

Examples of this system may occur as pine dominated woodlands, with Pinus palustris dominating some sites within its range, and Pinus echinata dominating areas where Pinus palustris is absent. Pinus taeda is naturally less common, but in the current landscape, it is common and sometimes dominant. Pines may co-dominate along with deciduous species, or the canopy may be dominated by oaks and other deciduous species including Quercus stellata, Quercus marilandica, Quercus incana, Quercus falcata, Quercus margarettae, and Carya texana (Elliott 2011). Other deciduous trees present may include Sassafras albidum, Liquidambar styraciflua, and Quercus nigra. The shrub stratum can be fairly well-developed, and includes shorter individuals of canopy species in addition to such species as Callicarpa americana, Ilex vomitoria, Vaccinium arboreum, Rhus aromatica, Asimina parviflora, Cornus florida, and Smilax bona-nox. The herbaceous layer may be quite well-developed or relatively patchy (with areas of bare sandy soil exposed). Commonly encountered species include Schizachyrium scoparium, Pteridium aquilinum, Aristida desmantha, Ambrosia psilostachya, Cnidoscolus texanus, Rudbeckia hirta, Dichanthelium dichotomum, Pityopsis graminifolia, Croton argyranthemus, Tragia urticifolia, Froelichia floridana, Matelea cynanchoides, Opuntia humifusa, Sporobolus junceus, Triplasis purpurea, Bulbostylis ciliatifolia, Chamaecrista fasciculata, Berlandiera pumila, Commelina erecta var. angustifolia, Stylisma pickeringii, Tetragonotheca ludoviciana, Tradescantia reverchonii, Rhynchosia spp., Tephrosia spp., Yucca louisianensis, as well as the fern ally Selaginella arenicola ssp. riddellii (Elliott 2011). All described community types in this system tend to support relatively open wooded canopies (<60% closure), and one type is described as essentially treeless. A degraded expression of this type has been described [see CEGL007507], but this is treated under the semi-natural ecological system. Other types are floristically differentiated, with special importance placed on the occurrence of Quercus arkansana.

This system type is found on droughty uplands underlain with deep, coarse sandy soils. It is generally associated with Eocene sand formations such as Carrizo, Sparta, and Queen City sands, including the Betis, Darco, Letney, Tehran, Tonkawa, and other Grossarenic or Psammentic soil series. It is also found on sands derived from the Pliocene Willis formation (Elliott 2011). These sites are typified by low fertility and moisture retention. In particular, these are found on deep sands on generally high, convex landforms, and often display a relatively open overstory canopy.

The primary natural processes controlling this system are droughty, deep sandy soils, and a natural fire regime. Fire is believed to have been a critical natural disturbance process which affected the vegetation structure and likely the species composition of communities in this system. There are several indirect pieces of evidence which suggest this: (1) Pinus echinata is intolerant of competition, and young stems are generally slower growing and slower to dominate sites than either Pinus taeda or many hardwood species (Lawson 1990); (2) Pinus echinata regeneration decreases dramatically with time since fire (Ferguson 1958); and (3) Pinus echinata has the ability to resprout. Watson (1986) postulates that most seedlings of Pinus echinata are killed during the periodic fires, and the mature trees are spared. This prevents the formation of thickets. This paper implies that low fuel levels accompany the sparse vegetation of these sandy areas, leading to a somewhat longer fire-return interval, which suits Pinus echinata. A variety of fire-return intervals have been estimated for Pinus echinata vegetation. Garren (1943) proposed an 8- to 10 -year return interval, Landers (1989) inferred a regime of 10 per century, and Martin and Smith (1993) estimated a 5- to 15 -year interval, however, none of these estimates were specific to Pinus echinata on sandhills. Many such sites in the region lack well -developed and continuous fine fuels necessary to ignite and spread fires, possibly due to site infertility and droughtiness (R. Evans pers. obs., L. Smith pers. comm.).

The primary threat to this system is conversion to pine plantations or other agriculture (e.g., watermelon farms), increase in canopy closure due to alterations of the natural fire regime, and conversion to developed land uses.

This system occurs west of the Mississippi River primarily outside the natural range of longleaf pine (Pinus palustris).