Upland Plant Communities
Upland communities include longleaf pine uplands, arid sandylands, and wetland pine savannahs. Well-drained uplands and ridges are home to longleaf pine upland forests mixed with shortleaf pine, loblolly pine, blackjack oak, bluejack oak, and post oak. Grasses and forbs (including Texas trailing phlox) form an herbaceous understory in this fire-dependent community when fires occur at frequent intervals. Arid sandylands are rare, occurring where ancient seas, rivers, and flood events deposited enough sand to form dunes and sandhills. They are characterized by scattered shrub patches and an overstory of longleaf pine; sand, bluejack, and post oaks; and scattered shortleaf, and loblolly pines. Because of low soil moisture, this community also supports a number of species adapted to dry conditions, including prickly pear cactus and yucca. Wetland pine savannahs contain the richest botanical diversity in the preserve with up to 100 species of forbs and grasses per acre. These communities occur on poorly drained soils where water ponds seasonally, which inhibits tree growth. Scattered longleaf pines form the overstory, while shrubs include sweetbay magnolia, gallberry holly, wax myrtle, and titi (pronounced ‘tie-tie’). Orchids and insectivorous plants can be found in the herbaceous layer along with sedges when soil moisture and light conditions are just right.
Slope Plant Communities
Increased soil moisture on slopes gives rise to distinct vegetation communities that gradate down the slope. The upper slope plant community of longleaf pine and southern red oak gives way to loblolly and shortleaf pines and white oak at mid-slope. This in turn changes to a beech-magnolia-loblolly forest along the lower slope where wetter soil conditions prevail. Dominant shrubs also change with their location on the slopes going from yaupon, flowering dogwood, and beautyberry to midslope and lower slope shrubs of American holly, American hornbeam, and horse sugar. Sweetgum and blackgum trees may also be present in the wetter, lower slopes. Because of the rarity of these forest types, the Texas Natural Heritage Program considers them imperiled. There is also new evidence that beech-magnolia-loblolly forests are declining, perhaps because of increasing summer temperatures that could be related to global climate change.
Floodplain Plant Communities
Big Thicket’s has several floodplain vegetation community types including bottomland floodplains, baygalls, palmetto hardwood flats forests, and cypress sloughs. Bottomland floodplains feature trees such as loblolly pine, American beech, American hornbean, sweetgum and water oak. They occur in the areas flooded each year by the rivers and larger streams of the Big Thicket. Baygalls are shrub thickets found along the broad floodplain of the Neches River. Baygalls can also be found in wetland pine savannas and areas containing springs, seeps, and ponds. The term “baygall” is derived from the occurrence of sweetbay magnolia and gallberry holly, two dominant plants in these communities. Palmetto hardwood flats occur in flat, poorly drained areas where water forms ponds for significant periods of time. Dominant tree species include overcup oak, willow oak, and laurel oak. Abundant sandy mounds also characterize this plant community type and represent small, drier “islands” that often support loblolly pine. Dense thickets of jungle-like dwarf palmetto frequently dominate the understory. Bald cypress and water tupelo are the dominant tree species of the cypress sloughs found in secondary river and creek channels and along the edges of oxbow lakes and sloughs throughout the preserve. These primordial forested swamps were once found throughout the Big Thicket region, but now are extremely rare because of extensive cypress logging and river channelization during the last century.