West Gulf Coast Seepage Swamp

This West Gulf Coastal Plain ecological system consists of forested wetlands (often densely wooded) in acidic, seepage influenced wetland habitats. These wetlands may occur in poorly developed upland drainages, toeslopes, and small headwaters stream bottoms. These environments are prone to long duration standing water, and tend to have highly acidic, nutrient-poor soils. The vegetation is characterized by an overstory of Magnolia virginiana, Nyssa sylvatica, Nyssa biflora, and Acer rubrum, although there is some variation according to latitude. Understory vegetation throughout the region consistently supports the vines Smilax laurifolia and Smilax walteri, and a dense abundance of ferns, such as Osmunda cinnamomea, Osmunda regalis var. spectabilis, and Woodwardia areolata. In most cases, these wetlands are embedded in uplands with deep sandy soils, recharge areas for this wetland system. When these communities are associated with streams, they tend to be low gradient, with narrow, often braided channels and diffuse drainage patterns. Due to excessive wetness, these habitats are normally protected from fire except those which occur during extreme droughty periods. The limited examples in Oklahoma are somewhat depauperate and lack some of the more southern and eastern taxa (e.g., Magnolia virginiana, Nyssa biflora).

Examples of this system are characterized by overstory species such as Magnolia virginiana, Nyssa biflora, and Acer rubrum. Other species in the overstory may include Fraxinus pennsylvanica, Quercus nigra, Liquidambar styraciflua, and Quercus laurifolia. A well-developed woody understory is often present and includes species such as Morella caroliniensis, Itea virginica, Persea palustris, Rhododendron prinophyllum, Rhododendron canescens, Ilex decidua, Vaccinium fuscatum, Ilex opaca, Toxicodendron vernix, Viburnum nudum, Morella cerifera, Alnus serrulata, Smilax laurifolia, and Vitis rotundifolia. There is some variation with latitude. Southerly examples generally consist of broad-leaved evergreen forests, while more northerly examples support more mixed evergreen-deciduous forests. In addition, evergreen species are especially pronounced in the shrub layer of southern examples. Southern expressions of the type are more likely to have Ilex coriacea and/or Cyrilla racemiflora. The herbaceous layer is often dominated by ferns such as Woodwardia areolata, Osmunda regalis, Osmunda cinnamomea, and Athyrium filix-femina. Carex spp., Rhynchospora spp., and Eleocharis spp. are also frequently encountered. Sphagnum occurs in patches throughout, and other bryophytes are common. The rare species Bartonia texana may be encountered in this system, along with other interesting forbs such as Burmannia biflora and Apteria aphylla (Elliott 2011).

This system occurs on saturated soils associated with springs and seepage flow in a variety of landscape positions. In the Outer Coastal Plain, these settings tend to be low landscape positions typically along low-gradient creeks, headwaters of drainages, or local depressions (Elliott 2011). The low-gradient creek channels tend to be highly meandering, often with multiple channels and extremely shallow banks. Nixon et al. (1983a) measured stream depths of 0.3-0.6 m and widths of less than 1 m in a study of this system. Inner Coastal Plain examples tend to be embedded within deep sandy slopes and uplands, and may also occur in association with flatwoods drainages (Martin et al. 1990, Martin and Smith 1991, Smith 1996a, Singhurst pers. comm. 2013). It may occur on a range of geological formations, including intermediate to high Pleistocene terraces, Eocene sands, the Catahoula Formation, and the Wilcox Formation. Soils are typically sandy to loamy soils, often with an impermeable subsurface layer that restricts water percolation. These sites are typically semipermanently saturated. These are typically soils of medium to strong acidity, with low available nutrients and significant organic accumulation (Elliott 2011). The deep, poorly drained, strongly acidic, loamy fine sand soils have high organic matter content (Brooks et al. 1993). Van Kley (1999a) indicates that these habitats, sometimes mapped as the Betis soil series and Guyton soil complex, are notably low in calcium and magnesium. Soils of other examples may be mapped as Lovelady (Arenic Glossudalf), Rentzel (Arenic Plinthaquic Paleudult), Corrigan (Typic Albaqualf), Melhomes (Humaqueptic Psammaquent), and Osier (Typic Psammaquent). This system is known from the Pleistocene Terraces and Tertiary uplands in Louisiana, Texas, Arkansas and to a limited extent in Oklahoma. Geologic formations where this system occurs include: Bentley (Intermediate Pleistocene Terraces), Willis (High Pleistocene Terraces), Fleming (Miocene), Catahoula (Oligocene), Cockfield (Eocene), Sparta (Eocene), Carrizo (Eocene), Wilcox (Eocene), Queen City (Eocene) and possibly the Vicksburg (Oligocene) and other formations.

This system is maintained by groundwater seepage. Soils have high available water capacity and surface runoff is very slow to ponded. This ecological system is embedded within fire-maintained systems. The role of fire in this system was probably minimal except during droughts or in narrow occurrences where fire may have maintained an example of this system dominated by Arundinaria gigantea.

Habitat loss, fragmentation, hydrological alterations (e.g., damming for small impoundments), and sedimentation are the primary threats facing this ecological system. Its current extent is estimated to be only 25 to 50% of its original extent in Louisiana. Remaining occurrences are often surrounded by degraded or converted habitats and are impacted by forestry and other land management practices (LDWF 2005). Hydrologic alterations that degrade and destroy this ecological system include, but are not limited to, channelization of rivers of streams, drainage ditches, development of infrastructure, and groundwater removal. Other threats include physical damage from nearby and on-site land management activities, eutrophication within urban and agricultural landscapes (from nutrient-laden stormwater runoff), invasive exotic plants such as Lonicera japonica, Ligustrum sinense, Microstegium vimineum, and feral hog (Sus scrofa) rooting. Intense wildfire can also be a threat. If changes in regional climate bring about a decrease in precipitation, this could lead to drying and loss of this system.

This system is restricted to eastern Texas, western Louisiana, southern Arkansas, and extreme southeastern Oklahoma.