Texas-Louisiana Coastal Prairie

This system encompasses non-saline tallgrass prairie vegetation that developed over Pleistocene terraces flanking the Gulf Coast of Louisiana and Texas. It is sometimes characterized by a ridge-and-swale or mound-and-intermound microtopography and encompasses both upland and wetland plant communities. Upland dominants typically include Schizachyrium scoparium, Paspalum plicatulum, and Sorghastrum nutans. Wetland dominants in undisturbed occurrences include Panicum virgatum and Tripsacum dactyloides. Fire is an important ecological process in this system.

Stands are dominated by graminoid species, such as Andropogon gerardii, Andropogon glomeratus, Bouteloua curtipendula, Cyperus entrerianus, Dichanthelium oligosanthes, Fimbristylis puberula, Muhlenbergia capillaris, Panicum virgatum, Paspalum floridanum, Paspalum plicatulum, Paspalum setaceum, Rhynchospora spp., Schizachyrium scoparium, Sorghastrum nutans, Sporobolus compositus, Tridens strictus, and Tripsacum dactyloides. Axonopus spp., Andropogon virginicus, Bothriochloa laguroides ssp. torreyana, Nassella leucotricha, and Sporobolus indicus may be particularly noticeable on overgrazed sites; disturbed occurrences may be dominated by Andropogon glomeratus. Non-native graminoids that may be conspicuous to dominant components include Cynodon dactylon, Bothriochloa ischaemum var. songarica, Dichanthium spp., Lolium perenne, Schedonorus arundinaceus (= Schedonorus phoenix), Paspalum notatum, and Paspalum dilatatum. Forbs that may often be encountered include Liatris spp., Sabatia campestris, Ambrosia psilostachya, Euphorbia bicolor, Solidago spp., Rudbeckia hirta, Ruellia humilis, Asclepias viridis, Chamaecrista fasciculata, Helianthus angustifolius, Euthamia spp., Ratibida columnifera, Symphyotrichum ericoides, Silphium laciniatum, Baptisia spp., Iva angustifolia, Eryngium yuccifolium, Boltonia diffusa, and Neptunia lutea. Woody species may invade this typically herbaceous vegetation, including Rosa bracteata, Vachellia farnesiana (= Acacia farnesiana), Triadica sebifera, Baccharis halimifolia, Celtis laevigata, and Prosopis glandulosa (Elliott 2011).

This mid- to tallgrass prairie occupies Pleistocene surfaces of the Texas and Louisiana coast, on non-saline soils. The occurrence of this system is generally coincident with the distribution of the Pleistocene Beaumont and Lissie formations in Texas (Prairie and Intermediate allogroups in Louisiana). It is usually found on level to gently rolling landscapes, with slopes generally less than 5%. Microtopography plays an important role in local variation in the system, with ridges, swales, mounds, depressions, mima (or pimple) mounds, and gilgai leading to a mosaic of drier and wetter plant communities. Typical soils are non-saline Vertisols, Alfisols, and (less extensively) Mollisols (Diamond and Smeins 1984, Smeins et al. 1992). Vertisols are often characterized by gilgai, resulting from shrink-swell attributes of the montmorillonitic clays of which they are composed. Historically, rivers and streams dissected this vegetation type, breaking it into large compartments with species composition shifting across the range. A moisture gradient occurs from northeast (average 120 cm/year) to southwest (average 100 cm/year) across the range of this system (Diamond and Smeins 1984).

The impacts and interaction of fire, drought, competition, and possibly grazing constitute the major natural dynamics influencing this system (Smeins et al. 1992, USGS 2013). Frequent fires every 2-5 years of both lightning and anthropogenic origins prevent woody species from establishing and favor grassland species adapted to fire for reproduction and vigor. Microtopographic and moisture variability interacted with fire to produce variable fire effects influencing the distribution of flora and fauna. Grazing by bison and other ungulates also played an important role in maintaining the vegetation composition and structure of this system. This system is important for a suite of wildlife, many of which are declining, that are dependent on native grasslands (TPWD 2012a).

This prairie system once covered as much as 9 million acres and less than 1% is thought to remain (Smeins et al. 1992, Bergan 1999, USFWS and USGS 1999, Grace et al. 2000, LDWF 2005, USGS 2013). This loss was caused by conversion to other land uses (primarily rice and sugarcane farming, pasture, and residential and commercial development) and environmental degradation due to the interruption of important ecological processes, such as fire, needed to maintain this system. In the absence of regular fire, this system will be invaded by woody shrubs and trees. Remaining occurrences continue to be threatened by conversion to other land uses (agriculture, pasture, and residential and commercial development), overgrazing, and loss of landscape level natural processes (Smeins et al. 1992, Bergan 1999, USFWS and USGS 1999, Grace et al. 2000, LDWF 2005, USGS 2013). Fire suppression and overgrazing have allowed native and non-native woody species to invade. If changes in regional climate bring about an increase in precipitation, this could lead to an increase in woody encroachment; a decrease in precipitation could lead to loss of the wet prairie components of this system. Due to its proximity to the coast and coastal marshes, sea-level rise could further impact this system by saltwater inundation and increased salinity.

This system occurs within 50 to 150 miles of the Gulf Coast from southwestern Louisiana to south-central Texas encompassing approximately 10 million acres.