West Gulf Coast Wet Longleaf Pine Savanna

This system was the historical matrix vegetation of the outer (seaward) portions of the West Gulf Coastal Plain between the coastal prairies and the inner coastal plain in Louisiana and eastern Texas within the range of longleaf pine. These areas are characterized by poorly drained upland soils with high and highly fluctuating water tables. In natural condition, monospecific stands of Pinus palustris and species-rich herbaceous layers characterize this system. Other species in the canopy include Quercus stellata, Quercus marilandica, Nyssa sylvatica, Quercus laurifolia, Quercus falcata, and Liquidambar styraciflua. Shrubs are typically limited in distribution within the system to local topographic highs and include species such as Morella cerifera, Ilex vomitoria, Symplocos tinctoria, Cyrilla racemiflora, and others. Widespread alterations following European settlement, including changes to natural fire regimes, have produced drastic changes to this system, and few large examples are extant. Examples appear to be somewhat more common in western Louisiana than in eastern Texas.

This system may be characterized as having a sparse canopy (under natural fire cycles) dominated by Pinus palustris. Other species in the canopy include Quercus stellata, Quercus marilandica, Nyssa sylvatica, Quercus laurifolia, Quercus falcata, and Liquidambar styraciflua. Shrubs are typically limited in distribution within the system to local topographic highs and include species such as Morella cerifera, Ilex vomitoria, Symplocos tinctoria, Cyrilla racemiflora, and others. The herbaceous layer may be highly diverse. Drier sites may be dominated by Schizachyrium scoparium, Schizachyrium tenerum, Eupatorium rotundifolium, and others. Wetter sites may not have species showing a clear dominance. Species such as Liatris spp., Xyris spp., Rhexia spp., Rhynchospora spp., Fuirena spp., Marshallia graminifolia, Aletris aurea, and many other species may share dominance in this system. Suppression of fire has lead to increased woody dominance. Pinus taeda, Pinus elliottii, Liquidambar styraciflua, Nyssa sylvatica, and Acer rubrum may now dominate the canopy of these sites, with a thick understory dominated by Ilex vomitoria and Morella cerifera (Elliott 2011).

This system represents the presumed matrix vegetation on relatively recent (Pleistocene) geologic formations within the range of longleaf pine in the outer (seaward) portions of the West Gulf Coastal Plain between the coastal prairies and the inner coastal plain in Louisiana and eastern Texas. In Louisiana, these are mapped as the Intermediate Terrace and the upper Prairie Terrace (Snead and McCulloh 1984), and in Texas as the Lissie Formation and the upper Beaumont Formation (Sellards et al. 1932). The Intermediate Terrace of Snead and McCulloh (1984) includes terraces formerly designated as the Montgomery, Irene, and most of the Bentley. These areas are characterized by poorly drained upland soils with high water tables (Bridges and Orzell 1989a). Landforms include mesic to seasonally saturated low areas and flats, on level to gently rolling uplands. Microtopographic variation is provided by the presence of swales and pimple mounds. Soils are sandy to silty loams that are strongly acidic, nutrient poor, and low in organic constituents. Typically these soils are hydric, with seasonal fluctuations between saturation and droughtiness (Elliott 2011). Within the range of longleaf pine, this system is bounded on the landward side by West Gulf Coastal Plain Upland Longleaf Pine Forest and Woodland (CES203.293).

Frequent fires (every 1-4 years), seasonal wetness and low nutrient availability of this ecological system inhibit the establishment of woody understory species and maintain a sparse canopy of longleaf pine (Stambaugh et al. 2011a and others). This frequent fire regime is necessary to maintain the open savanna condition and provides bare ground for Pinus palustris regeneration. Current examples must be managed with prescribed fire. Fires are usually low in intensity overall, consuming only shrubs and herbs, but will occasionally kill patches of young pine regeneration and rarely kill individual older trees. Historically, individual fires covered extensive areas. This high fire frequency is dependent on the presence of fine fuels in the form of grasses and other graminoids. Prescribed fire has been used as an attempt to reverse the effects of decades of fire suppression. However, the results of these attempts have been mixed. Uncertainty remains over the frequency of burning necessary to restore fire-dependent ecosystems; however, a return frequency of every 2-5 years appears best. Application of burns is often too infrequent, allowing woody understory species to crowd out longleaf or, in hardwood forests, oaks, beeches and other dominant trees. Similarly, burns are ineffective if applied at the wrong life stage of plants or at the wrong point in the growing season. An example: late-spring to early-summer burns favor longleaf and associated herbaceous plants, whereas late-season or winter burns favor woody shrubs. However, prescribed burns, properly applied, are a crucial restoration and management tool in the pyrogenic longleaf pine ecosystems. Canopy gaps are created by fire mortality, lightning, and windthrow from hurricanes and tornados.

This ecological system is much reduced form its original extent. Today, only 1 to 5% of this system remains in Louisiana (Smith 1993). Current examples of this ecological system are primarily threatened by drainage, other forms of physical damage form logging, and conversion to residential and commercial development and pine plantations (LDWF 2005). Longleaf pine forests were among the most valuable economic resources in the region at the turn of the twentieth century (Bray 1906). Overall losses of longleaf pine in Texas have exceeded those of all other southern states (Outcalt 1997); less than 16,200 hectares of mostly second-growth stands remain (McWilliams and Lord 1988). Land use practices continue to degrade remaining examples of longleaf pine communities (Bridges and Orzell 1989a).

Another primary threat is alteration of the natural fire regime. Longer fire-return intervals (10 years) will lead to significant woody encroachment of shrubs and fire-sensitive trees. This condition can also lead to increased fuel loading that will put the larger, more established trees at risk due to hotter, less frequent fires. An increase in cover of off-site woody species can suppress the regeneration and growth of species typical of this system in its natural state. Threats also include the limiting of prescribed burning due to urban interface, safety and smoke management concerns.

The proliferation of both invasive native and exotic vegetation is a negative impact on this ecosystem. Some native plants can be problematic in the absence of natural processes like fire. For example, Ilex vomitoria can crowd out other natives and become a dominant understory plant in some fire-suppressed areas. Most invasives are extremely difficult and costly to control once established. Other invasives already well-established include Triadica sebifera, Sus scrofa and non-native fire ants Solenopsis invicta.

If changes in regional climate bring about a decrease in precipitation, this could lead to drying and loss of this system.

This system is endemic to western Louisiana and eastern Texas, and examples appear to be somewhat more common in western Louisiana.