Atlantic Coastal Plain Sandhill Seep

This sandhill seep system occurs in small patches on slopes in dissected terrain, where a clay lens or other impermeable layer forces groundwater to the surface as seepage. This type occurs largely in the Fall-line Sandhills region of the Carolinas and Georgia but also rarely in other parts of the Atlantic Coastal Plain. Soils are seasonally to permanently saturated by seepage and range from sandy or clayey to mucky. Vegetation is variable and complex in composition and structure, consisting of a mixture of plants of pine savannas and streamhead pocosins, but contrasting with both in structure and proportions. The tree canopy of Pinus serotina and Pinus palustris may be open or rarely absent, and patches of dense shrubs, grasses, ferns, and various herbaceous plants may be present. Where burned every one to three years, Arundinaria tecta may be patch-dominant. Fire is a crucial determinant of structure and composition; it tends to occur in a variable and patchy pattern that is driven by both the fire regime of the surrounding system and the wetness of the seep vegetation.

Vegetation is a potentially diverse mixture of plants of wet savannas and pocosins. Vegetation structure may vary widely, with dense shrubs, dense herbs, or mixtures of shrubs and herbs, and with an open tree canopy or absent tree canopy occurring in complexes or in different patches. Pinus palustris, Pinus serotina, or several hardwood species may dominate the canopy. Characteristic Streamhead Pocosin shrubs, such as Ilex glabra, Lyonia lucida, Clethra alnifolia, Toxicodendron vernix, Ilex coriacea, and Zenobia pulverulenta, may mix with flatwoods shrubs, such as Gaylussacia frondosa and Kalmia carolina. The herbs are primarily species shared with wet savannas, such as Aristida stricta, Calamovilfa brevipilis, Ctenium aromaticum, Andropogon glomeratus, and a variety of showy forbs and insectivorous plants, but often occur in very different proportions. Large wetland ferns, such as Osmunda cinnamomea, Osmunda regalis, and Pteridium aquilinum, also often dominate. Where burned every one to three years, Arundinaria tecta (= Arundinaria gigantea ssp. tecta) may be patch-dominant.

This system occurs on gentle to steep slopes of dissected areas in interbedded sand and clay, largely in the Fall-line Sandhills region but rarely in other parts of the Atlantic Coastal Plain. Sites are seasonally to permanently saturated with seeping groundwater, forced to the surface by an impermeable layer such as a clay bed. Soils may be sandy, clayey, or in the wettest sites, mucky. The hydrological connection to adjacent Atlantic Coastal Plain Fall-line Sandhills Longleaf Pine Woodland (CES203.254), whose well-drained sandy soils are the source of seepage water, is crucial. Fire is a crucial natural force, and is also dependent on the adjacent systems. At Fort Benning, Georgia, examples of this system occur in wet mineral soils in zones between drier, sandhills longleaf pine communities and saturated streamside forests dominated by Nyssa biflora. In the Sandhills region of North Carolina, they may occur in a similar position between sandy uplands and streamhead pocosins, or they may occur as isolated wetlands on slopes surrounded by dry longleaf pine communities.

The ecological dynamics of the Sandhill seep are influenced by the amount and duration of saturation and the frequency and intensity of wildland fire. Fires can burn completely through Sandhill seeps, keeping shrub cover low and promoting graminoids and herbs (Nordman 2012). Fire is a natural dynamic process in this ecological system and is critical in determining the vegetation structure. Fires spread into seeps from surrounding or upslope Pinus palustris-dominated woodlands, which naturally burned every few years. Due to the high moisture availability, the vegetation of the seep grows quickly. The graminoid plants and evergreen shrubs together burn easily, except for the bases of the plants which tend to remain wet from seepage water. Some fires do not penetrate parts of the seeps, creating variable age and vegetation structure. Areas that have not burned recently or seldom burn have dense and tall shrubs, while areas that burn frequently are dominated by herbs, usually with patches of Arundinaria tecta. With long absence of fire, many seeps become indistinguishable from Atlantic Coastal Plain Streamhead Seepage Swamp, Pocosin and Baygall (CES203.252). Canopy dynamics are driven by soil saturation and fire, with hot fires killing- trees and creating a fine mosaic or zoned complex of older trees, younger regeneration, and treeless areas. Shrubs and herbs readily sprout after fires, but relative proportions are controlled by the frequency of fire.

Threats include forestry site preparation, off-road vehicle use in the wet seep, lack of fire, feral hog (Sus scrofa) rooting (Engeman et al. 2007), and impoundment. Forestry site preparation can involve application of forestry herbicides, root rake, drum chop (single, double, light or deep), bedding, or push, pile and burn. Drier seeps that are not too steep may be subjected to these practices along with the surrounding lands, destroying the diverse herbaceous vegetation. Forestry activities in surrounding lands also alter or reduce the spread of future fires into seep ecological systems, reducing the frequency of fire in the seep. These seeps support various amphibians, which are sensitive to herbicides such as Atrazine (used in corn fields) and Glyphosate in formulations with the surfactant POEA (polyethoxylated tallow amine). Glyphosate is commonly used in forestry and management of invasive exotic plants. Choosing an appropriate herbicide, following forestry best management practices and label directions can reduce the threats from herbicides to non-target organisms.

Lack of fire is one of the most important threats. Without occasional or frequent fire, broadleaf shrubs and trees, such as Acer rubrum, Clethra alnifolia, Ilex coriacea, Ilex glabra, Liquidambar styraciflua, Liriodendron tulipifera, Lyonia lucida, Pinus taeda, Quercus nigra, and others proliferate and can reduce or eliminate the diverse herbaceous vegetation (Nordman 2012). When the Sandhill seep succeeds to a closed forest, then the herbaceous diversity at the site tends to decline dramatically, and without fire, the decline may continue. Off-road vehicle (ORV) use in wetland areas can cause significant disturbance and damage to sensitive habitats. Sandhill seeps which have been subjected to ORV use can become a ruderal herbaceous wetland habitat. Because many seeps occur on slopes, ORV use can also lead to soil erosion. Feral hogs root in the ground, disturbing the herbaceous vegetation and eating the roots of plants or amphibians and invertebrates which they find.

This system occurs from east-central North Carolina to central Georgia, primarily in the Fall-line Sandhills region but occasionally occurring in the Outer Coastal Plain. For example, this system occurs in limited parts of southeastern Georgia associated with the topography of old escarpments. It occurs primarily in the Atlantic drainage but is rarely represented in the Gulf drainage (such as at Fort Benning, Georgia).