Gulf Coast Interior Shortleaf Pine-Oak Forest

This forested ecological system of the East Gulf Coastal Plain occurs most extensively on generally rolling uplands north of the range of Pinus palustris. It was the historical matrix in large areas of the region in Alabama and Mississippi, particularly from about 32°30'N latitude (the approximate local northern limit of the historic range of Pinus palustris), north to about 35°N latitude (the approximate limit where relatively extensive examples of Pinus echinata are replaced by predominantly hardwood-dominated systems). It is also understood that isolated examples of this system may occur both north and south of these boundaries in limited areas, including in the "Florida Parishes" of Louisiana. Stands tend to occur on generally well-drained sandy or clayey soils with dry to dry-mesic moisture regimes. Pinus echinata is the dominant pine species of the generalized "dry and dry-mesic oak-pine" forest type in the Gulf Coastal Plain and is the most characteristic floristic component of this system. The actual amount of Pinus echinata present varies based on a number of factors, but intact examples of this system often include stands that are dominated by Pinus echinata grading into stands with a mixture of upland hardwoods. Locally, on mid to lower slopes, Pinus taeda may be a component, extending further upslope in the absence of fire. Fire is possibly the most important natural process affecting the floristic composition and vegetation structure of this system, although fire-return intervals are lower than those associated with East Gulf Coastal Plain Interior Upland Longleaf Pine Woodland (CES203.496). Pinus echinata may have difficulty replacing itself in the absence of fire, particularly on sites other than the driest ones. Local topographic conditions affecting natural fire compartment size generally lend themselves to this fire frequency, although some examples may have more frequent fires and some less than this generalized value. Where fire is most frequent the system may develop a relatively pure canopy of Pinus echinata typified by a very open woodland structure with scattered overstory trees and an herbaceous-dominated understory; such examples are rare on the modern landscape. More typical are areas in which Quercus spp., Carya spp., Liquidambar styraciflua, Liriodendron tulipifera, Acer spp., and Nyssa sylvatica have become prominent in the midstory and even overstory and in which herbaceous patches are rare. Although the general distributional boundaries described above indicate where this system formed an historical landscape matrix, smaller patches of the system may also be present in limited areas both north and south of these boundaries. Although some sources map the native range of shortleaf pine throughout a relatively large area of western Tennessee, the actual distribution of the species appears to be much more confined and almost absent from the Coastal Plain; when present, it occurs in only small stands on dry southwestern aspects.

This system is primarily composed of forest or woodland vegetation dominated by trees generally up to about 33 m (100 feet) in height. Individual patches or stands may be predominantly evergreen, predominantly deciduous, or mixed. The canopy will be primarily relatively closed (greater than 60%), but some areas may exhibit lower canopy closures, either as a result of repeated surface fires, timber removal, or other disturbances. This system includes the Shortleaf Pine-Oak Cover Type (Eyre 1980) as expressed in the Upper East Gulf Coastal Plain. In contrast to most of the Atlantic Coastal Plain, Pinus echinata is a much more ecologically and economically important species across much of the Gulf Coastal Plain, both presently and historically (Mohr 1901, Harper 1920, 1943). The actual vegetation composition depends greatly upon local site conditions, ongoing management, and disturbance history of an area. Locally, the species that comprise the system are strongly influenced by soil, slope, and aspect (Eyre 1980). Examples may be composed of various mixtures of pines and hardwoods. Although the actual amount of Pinus echinata present varies based on a number of factors, intact examples of this system often include stands that are dominated by Pinus echinata grading into stands with a mixture of upland hardwoods. Where fire is most frequent the system may develop a relatively pure canopy of shortleaf typified by a very open woodland structure with scattered overstory trees and an herbaceous-dominated understory; such examples are rare on the modern landscape. More typical are areas in which Pinus echinata trees occur in mixture with Quercus spp. and Carya spp. Many such areas also support Liquidambar styraciflua, Liriodendron tulipifera, Acer spp., and Nyssa sylvatica, and even Pinus taeda. When these species are prominent in the overstory and midstory it is generally though to be indicative of fire suppression. Quercus alba and Quercus stellata are common hardwood components, particularly in later-seral or higher-quality stands, typically combined with Carya tomentosa (= Carya alba), Carya pallida, Carya glabra, and other Carya spp. Higher-quality areas may exhibit somewhat open canopies. Other tree species indicative of recent disturbance and/or fire suppression are Quercus nigra, Quercus hemisphaerica, Quercus falcata, and Quercus velutina. Subcanopies will typically contain Cornus florida, Oxydendrum arboreum, Nyssa sylvatica, and Liquidambar styraciflua. The patchy shrub layer includes Vaccinium arboreum, Vaccinium elliottii, Asimina parviflora, Aesculus pavia, Hamamelis virginiana, Callicarpa americana, Hypericum hypericoides, Gelsemium sempervirens, Vitis rotundifolia, and Arundinaria gigantea. Herbs, which may be few and sparse, include Cnidoscolus urens var. stimulosus (= Cnidoscolus stimulosus), Indigofera caroliniana, Aristolochia serpentaria, Piptochaetium avenaceum, Chasmanthium sessiliflorum, Elephantopus tomentosus, Hexastylis arifolia, Iris verna, Rudbeckia fulgida, Solidago juncea, Euphorbia pubentissima, Mitchella repens, and Desmodium spp. (NatureServe Ecology unpubl. data 2003). Other associates may include Smilax spp., Symphyotrichum spp., Coreopsis spp., Lespedeza spp., Viola pedata, Mimosa microphylla, Antennaria spp., Clitoria mariana, Senna spp., Chasmanthium latifolium, Dichanthelium spp., Andropogon spp., Schizachyrium scoparium, and Carex spp. (Lawson 1990).

The core distribution of this system lies between about 32°30'N latitude and about 35°N latitude; more localized occurrences may be found as small patches both north and south of these boundaries embedded in other systems. The belted character of this region, in the form of inner lowlands and cuestas and other low-ridge landforms (Bowman 1911, Fenneman 1938), the associated diversity of soil types, and differences in settlement history appear to account for the importance of shortleaf pine in the Gulf Coast region when compared to the Atlantic Coastal Plain (White and Lloyd 1998). Cuestas and other hills create strong environmental gradients which, coupled with soil characteristics, promote a variety of mixed pine and pine-hardwood vegetation in this region; local differences in topography, parent material, and exposure influence site characteristics, resulting in numerous different plant communities. This system primarily occupies the dry and dry-mesic portion of regional moisture gradients. Wide variation in vegetation composition across this gradient is also strongly related to fire frequency and intensity (White and Lloyd 1998). Generally to the south and southeast it grades into longleaf pine-dominated system(s), and to the north into hardwood-dominated ones.

The frequent presence of surface fire is important in order to support the reproduction of Pinus echinata, which is a critical species characteristic to the system. Pinus echinata is a shade-intolerant species and does not survive or grow well when fire-suppressed. Outbreaks of Dendroctonus frontalis (Southern Pine Beetle) also play an important role in shaping the dynamics of this system and the balance of pine versus hardwood dominance over time. Young shortleaf pines are generally slower growing and slower to dominate a site than Pinus taeda or many hardwood competitors, but they usually will endure competition longer than the common associate, Pinus taeda. Pinus echinata can maintain dominance on most sites after it overtops competing vegetation, but in general hardwoods cannot be eliminated from pine sites. On very good sites (i.e., with high site index), however, it may not outgrow competing species such as sweetgum and red maple (Lawson 1990).

This system is restricted to the East Gulf Coastal Plain; it was the historical matrix in large areas of the region in Alabama and Mississippi, particularly between about 32°30'N latitude and about 35°N latitude. In southwestern Mississippi, this system is apparently dominant on the landscape west of 91°W longitude to the limits of the alluvial plain and northwest of a line running approximately from the intersection of 31°N latitude and 91°W longitude, northeastward to the city of Jackson, Mississippi, extending at least to about 34°N latitude. This is consistent with the ranges of Oak-Pine vegetation (generally equivalent to this system) versus Longleaf-Loblolly-Slash Pines in Shantz and Zon (1924). There are also limited and sporadic occurrences in the "Florida Parishes" of Louisiana (LNHP 2009).