The ecoregion covers an area of , extending along the shore of the
Gulf of Mexico from southeastern
Louisiana (west of the
Mississippi Delta) through
Texas and into the Mexican state of
Tamaulipas as far as the
Laguna Madre. Specific areas include a number of
barrier islands, and the
resacas or natural
levees of the Laguna Madre. The coast is vulnerable to tropical storms that can seriously damage habitats. This ecosystem, in part, has
edaphic origins: the soils of this ecoregion feature poor internal drainage, often under
alfisols and
vertisol. In combination with frequent fires, tree seedlings have a harder time settling, allowing grasses and other herbaceous species to dominate. This process is understood in the context of "subtropical hyperseasonal grasslands", similar to the
Florida dry prairie. However, there are interspersed areas of higher
sand and
silt content that break up the otherwise heavy clay environment: these areas typically correspond to
floodplain/
riparian zones, and are more permissive of tree-growth, featuring
galleries or even closed-canopy
bottomland expanses. ==Climate==