Ecological dynamics
U.S. National Vegetation Classification (USNVC) associations that are consistent with reference conditions on this ecological site include CEGL004468 Gaylussacia frondosa - Clethra alnifolia - Arundinaria tecta / Aristida stricta - Pteridium aquilinum var. pseudocaudatum, and CEGL004467 Clethra alnifolia - Toxicodendron vernix / Aristida stricta - Osmunda cinnamomea - Sarracenia spp., with the latter representing the innermost zone and the former representing the slightly drier, outer zone (USNVC 2023).
Hillside seeps of the Sandhills region are small, localized seepage-fed slope wetlands. In the reference state, with frequent fire, herb and shrubs dominate, though widely spaced trees can also be present. These wetlands are usually heterogeneous in cover and often visibly zoned in response to gradients of soil wetness and fire penetration. While seeps with little recent fire may be covered with shrubs throughout, even frequently burned seeps often have a wetter inner zone dominated by woody plants.
Wetlands of this type are known colloquially as seepage bogs. However, the term "bog," as applied here, is a technical misnomer, since these environments are not true peatlands, but rather nutrient-poor mineral wetlands with only limited organic matter accumulation at the surface. Further, these wetlands are not solely fed by precipitation, as they receive shallow groundwater from upslope. This term however, is widely used in the southeastern United States as a label for open, acidic seepage wetlands. This term will be retained here (for simplicity) to maintain congruence with other literary sources.
Seepage bogs of the Sandhills are extremely dependent on fire to maintain their open structure and characteristic herb diversity. Without fire, shrubs quickly expand to cover the entire site, and herb cover can be reduced or eliminated. Though fire ordinarily spreads from the surrounding longleaf pine-dominated uplands, the interaction of fire between drier uplands and seepage-fed wetlands is complex.
Many seeps show evidence of variable fire penetration, with a tall, unburned shrub zone in the center, a zone of intermediate fire penetration away from this zone, and a more frequently burned outer zone along the margins. These communities likely exhibited significant temporal variation, with shrub cover expanding and contracting over time. While the outer zone will likely burn every time fire moves across the landscape, the wetter inner zones usually dampen the spread of fire toward the center. Even if ignited, the innermost zone does not usually carry fire efficiently except during dry spells. However, as the source of ground water is local, shallow, and has limited residence time, the hydroperiod can vary greatly from year to year, periodically allowing fire to infiltrate the seep's innermost zone, while also allowing upland species to establish along its margins.
This ecological site is one of the principle habitat for the pine barrens tree frog (Hyla andersonii), a protected species found in wetlands of the Sandhills region. These frogs generally prefer acidic wetlands and are often found in the shrubbery around seepages. This species requires small-diameter woody vegetation for calling posts, which are found readily on this ecological site. Other wildlife that utilize hillside seeps include the Swainson’s warbler (Limnothlypis swainsonii), the prairie warbler (Dendroica discolor), the American woodcock (Scolopax minor), and the great crested flycatcher (Myiarchus crinitus) (Means and Moler 1979; Barry 1980; Wharton et al. 1978; Nelson 1986; Schafale and Weakley 1990; Peet 2007; USFWS 2010, 2014; Schafale 2012a, 2012b; Edwards et al. 2013; SCDNR 2015).
Canopy layer (where present): Pinus serotina, Liriodendron tulipifera, Acer rubrum, Persea palustris, Magnolia virginiana, Pinus palustris,
Shrub layer: Clethra alnifolia, Gaylussacia frondosa, Toxicodendron vernix, Arundinaria tecta, Kalmia latifolia, Leiophyllum buxifolium, Smilax laurifolia, Cyrilla racemiflora, Ilex glabra, Lyonia ligustrina, Lyonia mariana, Lyonia lucida, Vaccinium fuscatum, Kalmia carolina, Alnus serrulata, Viburnum nudum, Ilex opaca, Morella caroliniensis, Aronia arbutifolia, Kalmia cuneata, Amelanchier obovalis, Lindera subcoriacea, Rhododendron atlanticum, Fothergilla gardenii
Herb layer – forbs: Osmunda cinnamomea, Sarracenia spp. (rubra, purpurea var. venosa, flava), Xyris spp. (caroliniana, platylepis, scabrifolia, ambigua, chapmanii), Eupatorium spp. (pilosum, rotundifolium, leucolepis), Polygala lutea, Sphagnum spp., Lobelia nuttallii, Lobelia batsonii, Rhexia spp. (petiolata, lutea, alifanus, mariana), Utricularia spp., Woodwardia areolata, Pycnanthemum flexuosum, Woodwardia virginica, Bidens aristosa, Solidago salicina, Symphyotrichum dumosum, Osmunda spectabilis, Hexastylis sorriei, Calopogon tuberosus, Pogonia ophioglossoides, Cleistes divaricata, Cleistes bifaria, Spiranthes cernua, Lycopodium spp., Platanthera ciliaris, Anchistea virginica, Erigeron vernus, Desmodium tenuifolium, Pinguicula caerulea, Lilium catesbaei, Asclepias rubra, Burmannia biflora, Lysimachia asperulifolia, Platanthera clavellate, Lachnocaulon anceps, Marshallia graminifolia, Eryngium integrifolium, Gentiana autumnalis, Syngonanthus flavidulus, Pyxidanthera barbulata, Oxypolis ternata, Drosera spp. (capillaris, brevifolia, rotundifolia), Coreopsis linifolia, Doellingeria sericocarpoides, Chaptalia tomentosa, Ludwigia hirtella, Ludwigia virgata, Eriocaulon decangulare, Eriocaulon texense, Calopogon barbatus, Eriophorum virginicum, Triantha racemosa, Lilium pyrophilum
Herb layer – graminoids: Aristida stricta, Aristida beyrichiana, Ctenium aromaticum, Muhlenbergia expansa, Andropogon spp., Dichanthelium strigosum, Dichanthelium dichotomum var. ensifolium, Chasmanthium laxum, Glyceria obtusa, Scleria triglomerata, Scleria ciliata, Calamovilfa brevipilis, Fimbristylis spp., Juncus scirpoides, Carex collinsii, Carex styloflexa, Sporobolus pinetorum,
State 1
Reference State - Hillside Seepage Bog
Figure 8. A typical hillside seep under reference conditions.
Hillside seeps are dynamic systems, undergoing considerable change over time in response to natural disturbances. Shrubs expand and contract as cycles of drought give rise to differential penetration of fire, allowing shrub and herb cover to expand and contract over time.
Characteristics and indicators. Although rarely abundant, emergent trees may be present in small numbers. The most common species overall is pond pine (Pinus serotina). If present, trees are usually widely spaced or confined to the wetter, innermost zone.
Community 1.1
Hillside Shrub-Herb Bog
This community phase is dominated by a mixture of shrubs and herbaceous plant species. It typically develops in the interval between fires, or as a result of a slightly lower fire frequency than is required for long-term maintenance of community phase 1.2.
Resilience management. While this community phase briefly transitions to herb dominance with a single low-intensity fire event, long-term maintenance of shrub-herb codominance can be achieved with a fire return interval of approximately 2 to 4 years. This is the optimal condition for the pine barrens tree frog (USFWS 2010, 2014).
Dominant plant species
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coastal sweetpepperbush (Clethra alnifolia), shrub
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blue huckleberry (Gaylussacia frondosa), shrub
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poison sumac (Toxicodendron vernix), shrub
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switchcane (Arundinaria tecta), shrub
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mountain laurel (Kalmia latifolia), shrub
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sandmyrtle (Leiophyllum buxifolium), shrub
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swamp titi (Cyrilla racemiflora), shrub
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inkberry (Ilex glabra), shrub
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staggerbush (Lyonia), shrub
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black highbush blueberry (Vaccinium fuscatum), shrub
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threeawn (Aristida), grass
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toothache grass (Ctenium aromaticum), grass
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cutover muhly (Muhlenbergia expansa), grass
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bluestem (Andropogon), grass
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roughhair rosette grass (Dichanthelium strigosum), grass
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cypress panicgrass (Dichanthelium dichotomum var. ensifolium), grass
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slender woodoats (Chasmanthium laxum), grass
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Atlantic mannagrass (Glyceria obtusa), grass
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whip nutrush (Scleria triglomerata), grass
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fringed nutrush (Scleria ciliata), grass
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cinnamon fern (Osmunda cinnamomea), other herbaceous
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pitcherplant (Sarracenia), other herbaceous
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yelloweyed grass (Xyris), other herbaceous
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thoroughwort (Eupatorium), other herbaceous
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orange milkwort (Polygala lutea), other herbaceous
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Nuttall's lobelia (Lobelia nuttallii), other herbaceous
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meadowbeauty (Rhexia), other herbaceous
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netted chainfern (Woodwardia areolata), other herbaceous
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Appalachian mountainmint (Pycnanthemum flexuosum), other herbaceous
Community 1.2
Hillside Herb Bog
This community phase is dominated by herbaceous plant species. It can develop in the immediate aftermath of fire, serving as a transient plant community in the maintenance of community phase 1.1, or it can be maintained long term with increased fire frequency (1 to 2-year return interval).
Dominant plant species include a variety of grasses, sedges, and pitcher plants. Various orchids, lilies, and other showy species are frequently present, as well as numerous other carnivorous plants. The herb-dominated outer zones often give way to a shrub-dominated inner zone.
Resilience management. Herb dominance can be maintained long term with increased fire frequency. Woody vegetation is most effectively suppressed through warm-season burns (USFWS 2010, 2014).
Dominant plant species
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pond pine (Pinus serotina), tree
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switchcane (Arundinaria tecta), shrub
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threeawn (Aristida), grass
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toothache grass (Ctenium aromaticum), grass
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cutover muhly (Muhlenbergia expansa), grass
-
bluestem (Andropogon), grass
-
slender woodoats (Chasmanthium laxum), grass
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Atlantic mannagrass (Glyceria obtusa), grass
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whip nutrush (Scleria triglomerata), grass
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cypress panicgrass (Dichanthelium dichotomum var. ensifolium), grass
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roughhair rosette grass (Dichanthelium strigosum), grass
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fimbry (Fimbristylis), grass
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cinnamon fern (Osmunda cinnamomea), other herbaceous
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pitcherplant (Sarracenia), other herbaceous
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yelloweyed grass (Xyris), other herbaceous
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thoroughwort (Eupatorium), other herbaceous
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orange milkwort (Polygala lutea), other herbaceous
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sphagnum (Sphagnum), other herbaceous
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Nuttall's lobelia (Lobelia nuttallii), other herbaceous
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meadowbeauty (Rhexia), other herbaceous
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bladderwort (Utricularia), other herbaceous
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netted chainfern (Woodwardia areolata), other herbaceous
Community 1.3
Hillside Shrub Bog
This community phase is dominated by shrubs and vines. It typically develops in the interval between fires, as a result of a long inter-fire period (~4 to 10 years), or as a result of other fire-related variables such as fire intensity and timing. Because of the vicissitudes of unpredictable drought, the intensity of fires and the extent to which they burn into the seep can vary significantly. In the past, shrub cover would have presumably expanded naturally during periods of higher overall precipitation. With a prescribed burn of appropriate intensity and timing, it readily transitions to community phase 1.1 with fire (Means and Moler 1979; USFWS 2010, 2014).
Dominant plant species
-
coastal sweetpepperbush (Clethra alnifolia), shrub
-
blue huckleberry (Gaylussacia frondosa), shrub
-
poison sumac (Toxicodendron vernix), shrub
-
laurel greenbrier (Smilax laurifolia), shrub
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mountain laurel (Kalmia latifolia), shrub
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sandmyrtle (Leiophyllum buxifolium), shrub
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swamp titi (Cyrilla racemiflora), shrub
-
inkberry (Ilex glabra), shrub
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staggerbush (Lyonia), shrub
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black highbush blueberry (Vaccinium fuscatum), shrub
Pathway 1.1A
Community 1.1 to 1.2
The hillside shrub-herb bog readily transitions to the hillside herb bog through fire. In the past, under the natural fire regime, this community pathway presumably happened regularly with low-intensity fires that spread from the surrounding landscape. Herb dominance can be maintained long term through an increase in fire frequency (1 to 2-year return interval).
Pathway 1.1B
Community 1.1 to 1.3
In the absence of disturbance, the hillside shrub-herb bog naturally moves toward the hillside shrub bog through natural succession.
Pathway 1.2A
Community 1.2 to 1.1
In the absence of disturbance, the hillside herb bog naturally moves toward the hillside shrub-herb bog through natural succession.
Pathway 1.3A
Community 1.3 to 1.1
The hillside shrub bog readily transitions to the hillside shrub-herb bog through fire. In the past, under the natural fire regime, this community pathway presumably happened regularly with low-intensity fires that spread from the surrounding landscape.
Pathway 1.3B
Community 1.3 to 1.2
The hillside shrub bog can transition to the hillside herb bog through high-intensity fire. In the past, this may have occurred in response to months or consecutive years of dry soil conditions, allowing fire to penetrate more effectively and burn at higher intensity.
Context dependence. This community pathway is most likely during periods of severe drought, following several years without fire. Under periods of normal precipitation, fires that spread from the surrounding landscape are usually of lower intensity, as represented by community pathway 1.3A
State 2
Pond Pine Seepage Woodland
This state begins to develop with reduced fire frequency (~10 to 20 years). In response, cover from trees begins to increase, with pond pine (Pinus serotina) typically being the most common species. Other important species that begin to establish include sweetbay (Magnolia virginiana), swamp bay (Persea palustris), red maple (Acer rubrum), and tuliptree (Liriodendron tulipifera), among others. Scattered longleaf pines may also be present. Shrub cover is dense in the understory and herb cover is sparse (Sutter and Kral 1994; USFWS 2010, 2014).
Dominant plant species
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pond pine (Pinus serotina), tree
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sweetbay (Magnolia virginiana), tree
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swamp bay (Persea palustris), tree
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red maple (Acer rubrum), tree
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American holly (Ilex opaca), tree
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sweetgum (Liquidambar styraciflua), tree
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longleaf pine (Pinus palustris), tree
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swamp titi (Cyrilla racemiflora), shrub
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sandmyrtle (Leiophyllum buxifolium), shrub
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inkberry (Ilex glabra), shrub
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mountain laurel (Kalmia latifolia), shrub
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laurel greenbrier (Smilax laurifolia), shrub
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coastal sweetpepperbush (Clethra alnifolia), shrub
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staggerbush (Lyonia), shrub
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Carolina laurel (Kalmia carolina), shrub
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blue huckleberry (Gaylussacia frondosa), shrub
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black highbush blueberry (Vaccinium fuscatum), shrub
State 3
Hillside Seepage Forest
In this closed canopy state, the canopy is dominated by hardwoods that have come in after prolonged periods without fire (≥ 20 years of fire exclusion). In the absence of fire, ecological dynamics are driven largely by canopy gaps caused by windthrow.
Transition T1A
State 1 to 2
The reference state can transition to the pond pine seepage woodland with ongoing exclusion of fire or reduced fire frequency (~10 to 20-year return interval). Under these conditions, cover from tree species begins to increase.
Transition T2A
State 2 to 1
Pond pine seepage woodlands can transition back to the reference state through a combination of prescribed burns and selective removals. For long-term maintenance of the reference state, increased fire frequency (< 10-year return interval) will be needed thereafter. Warm season burns are most effective as a restoration tool.
Though increased fire frequency is a critical part of restoration, fire alone is not usually sufficient to overcome the threshold needed to reestablish the unique ecological dynamics that characterize the reference state, wherein vegetation structure moves fluidly between shrub and herb dominance with fire.
Transition T2B
State 2 to 3
In the absence of fire, or with reduced fire frequency (≥ 20-year return interval), pond pine seepage woodlands can succeed to forest.
Transition T3A
State 3 to 1
Over time, the hillside seepage forest state can transition back to the reference state through a stand replacing disturbance (clear-cutting, catastrophic fire, etc.) followed by an increase in the frequency of fire (< 10-year return interval). This is a gradual process, as it can take a number of years to ameliorate the effects of long-term fire suppression, and many more to approximate the composition and diversity of species observed under reference conditions.
Constraints to recovery. Because forest patches associated with this ecological site are typically small and insular, seed sources for characteristic seep species tend to be scarce in the surrounding landscape. Recovery can be hastened to some extent by planting keystone species.
Transition T3B
State 3 to 2
The hillside seepage forest state can transition to the pond pine seepage woodland through prescribed burns, and if necessary, selective removals. Conditions needed to carry fire may take a number of years to restore. Increased fire frequency (< 20-year return interval) will be needed for long-term maintenance thereafter. Warm season burns are most effective as a restoration tool.
