Southern Coastal Plain Cypress Dome

This system consists of small forested wetlands, typically dominated by Taxodium ascendens, often with a dome-shaped appearance in which trees in the center of the depression are taller than those around the exterior. Examples are known from the Southern Coastal Plain (Omernik Ecoregion 75 and adjacent 65) of Florida and Georgia, extending into Alabama, Mississippi and Louisiana. Examples occupy poorly drained depressions which are most often embedded in a matrix of pine flatwoods or mesic to dry pine woodlands. The oldest and largest individual trees typically occupy the center of these domed wetlands, with smaller and younger individuals around the margins. Pools of stagnant, highly acidic water may stand in the center of these depressions ranging from 30-120 cm (1-4 feet) in depth, but becoming increasingly shallow along the margins. These sites are underlain by an impervious clay pan which impedes drainage and perches precipitation. Depending on fire regime and hydroperiod, some examples may have thick (50-100 cm) organic layers. In addition to Taxodium ascendens, other woody species may include Cephalanthus occidentalis, Clethra alnifolia, Hypericum chapmanii, Hypericum myrtifolium, Ilex myrtifolia, Eubotrys racemosa, Liquidambar styraciflua, Lyonia lucida, Morella cerifera, Nyssa biflora, and Styrax americanus.

According to Drew et al. (1998), dominant plant taxa include Taxodium ascendens, Nyssa biflora, Cephalanthus occidentalis, Liquidambar styraciflua, Clethra alnifolia, Lyonia lucida, and Styrax americanus. A few less typical upland depression ponds in Florida dominated by Nyssa sylvatica are also accommodated in this system for now (A. Johnson pers. comm.). Other species found in this system can include Nyssa ursina, Hypericum chapmanii, Hypericum myrtifolium, Ilex myrtifolia, Eubotrys racemosa (= Leucothoe racemosa), Morella cerifera, Lobelia floridana, Polygala cymosa, Carex striata, and Carex turgescens.

This system occurs in areas of low relief, occupying poorly drained to permanently wet depressions in uplands such as pine flatwoods or mesic to dry pine woodlands. Pools of stagnant, highly acidic water may stand in the center of these depressions ranging from 30-120 cm (1-4 feet) in depth, but becoming increasingly shallow along the margins (Monk and Brown 1965). Some examples may have thick (50-100 cm) organic layers (Drew et al. 1998). Some of the depressions are fed by groundwater, while others are dependent on local precipitation.

Cypress domes get their common name from the dome-shaped appearance in which trees in the center are taller than those around the sides (Monk and Brown 1965). The water draws down more frequently along the shallow margins than in the deeper center. This allows for more frequent recruitment of Taxodium ascendens seedlings along the edges, which are also exposed to more frequent wildland fire than the center of the ponds which remain flooded for longer durations. These two factors are reflected in the presence of large trees in the center and smaller trees closer to the edges of the ponds (FNAI 2010a), and greater amounts of herbaceous graminoid plants along the margins of the depression. Where fires are more frequent, open herbaceous vegetation is favored. Without periodic fires Taxodium ascendens may become less dominant as hardwood or bay canopy species increase and peat accumulates. Taxodium ascendens has fairly thick, fire-resistant bark and is tolerant of light surface fires; however, the seedlings and small Taxodium ascendens trees are vulnerable to fire (FNAI 2010a). When the forest canopy is harvested, the disturbed vegetation can transition to an herbaceous graminoid-dominated wetland, such as represented by the ecological systems East Gulf Coastal Plain Depression Pond (CES203.558) or Southern Atlantic Coastal Plain Depression Pond (CES203.262). Transitions like this can also occur in response to the natural disturbance dynamics of Coastal Plain depressions, in which the influences of flooding, hurricanes and occasional wildland fire (or lack of fire) can lead to vegetation transition from wooded to herbaceous, or without canopy disturbance, succession from herbaceous to wooded or wetland forest vegetation.

Threats include lack of fire, alteration to the hydrology, and damage to the herbaceous ground cover from vehicles, feral hog (Sus scrofa) rooting, plowlines, and ditching. Lack of fire has been a widespread threat, and generally only sites which are within an area managed for conservation have prescribed fires frequently enough to conserve the biological diversity of this open wetland habitat, especially the rim or herbaceous ecotone transition to upland. The lack of fire can lead to shrub and hardwood tree encroachment, increased shading and evapotranspiration, accumulation of leaf litter, and a drying out of the depression wetland during drier times of year. Since many of the herbaceous plants which grow around the edge or rim of these wetlands have corms, or starchy root structures, feral hogs are a real threat. Feral hogs will turn up the soil and eat the below-ground plant parts and amphibians and invertebrates that live in the wet soil. In doing this they disturb the soil and degrade the habitat. The areas of disturbed soil where feral hogs have rooted (or vehicles have rutted the wet soil) can provide habitat for weedy or invasive exotic plants. Also these disturbed soil areas are favored by red imported fire ants (Solenopsis invicta), which threaten amphibians using the depressions. On lands managed as pine plantations, sometimes shallow parts of cypress domes are bedded and planted in Pinus elliottii var. elliottii or Pinus taeda.

Examples are known from the Southern Coastal Plain (Omernik Ecoregion 75 and adjacent 65) (EPA 2004) of Florida and Georgia, extending into Alabama, Mississippi and Louisiana.