Big Thicket National Preserve
Plant Associations:
Appreciating The Nuances of Big Thicket
Upland Forests
Pine Sandhill: This is the driest of forests in Southeast Texas occuring on deep sandy terrace deposits along creeks and rivers. The best example in Big Thicket is in the southeast area of the Turkey Creek Unit. The Nature Conservancy's Sandyland Sanctuary is the largest example. These areas can be recognized by their low, open woodlands (short forest) with relatively sparse herbaceous layer and much exposed sand. There is a scattered overstory of longleaf, loblolly and shortleaf pines; the understory is a layer of oaks. Compositionally, these areas are characterized by abundant bluejack and post oaks. Prickly pear and yucca are also present.
Pine Forest: These forests are found on reasonably well-drained uplands typical of the northern area of the Big Sandy Creek Unit. They are also found in less drained units of the south. The overstory is strongly dominated by longleaf pine. The understory varies due to historic human use and can be a dense oak growth or a sparse growth of shrubs like sumac, sassafras, and wax myrtle. Where woody plants do not dominate, the herb layer is very dense and consists of many forbs and grass species - especially bluestem. Bluejack oak is absent or rare.
Pine Savannah Wetland: Savannah's occur in areas of poor drainage. Structurally, savannah's contain widely scattered longleaf pine usually the only tree present, although stunted individuals of blackgum and sweetgum may occur. Midstory shrubs are sweetbay, wax myrtle, titi, and gallberry holly. The herbaceous layer is diverse with insectivorous plants and orchids usually common. Sedges are also common; standing water is typical. In contrast, the Pine Sandhill and Pine Forest types seldom experience standing water. The Hickory Creek Savannah Unit (Sundew Trail) is the best example.
Slope Forests
Upper Slope Pine Oak: These are the driest of the Slope Forests. They tend to occupy the upper portions of slopes. Structurally, they are the shortest of the Slope Forests and are taller and more closed canopy than Upland Pine Forests. The dominant overstory species are shortleaf pine and red, post, or blackjack oaks, as single specimens or in any combination. Loblolly pine is almost always present. Dominant shrubs are yaupon, flowing dogwood, and beautyberry. The herbaceous layer is restricted because of the well-developed canopy. White oak is absent as a large overstory tree. A good example is found at the start of the Kirby Nature Trail in the Turkey Creek Unit.
Mid-Slope Oak Pine: These are taller, are more closed canopy and have a greater proportion of hardwoods in the overstory than the Upper Slope. Overstory dominant species are red oak, white oak, and loblolly pine. Magnolia and shortleaf pine may be present. Dominate shrubs are flowering dogwood, American holly, and yaupon. The herbaceous layer is poorly developed. Beech is absent while white oak is co-dominant. A good example is found along the Kirby Nature Trail in the Turkey Creek Unit.
Lower Slope Hardwood Pine: Found on the gentle to steep slopes near creeks and creek branches. They have a dense closed canopy and are dominated by beech, magnolia, and loblolly pine. Sweetgum, blackgum and oaks are occasionally present in the overstory and are common in the understory. Dominate understory species are American holly, red maple, American hornbeam, horse sugar, and yaupon. Herbs are severely restricted. Again, visit the Turkey Creek Unit along the lower sections of the Kirby Nature Trail.
Floodplain Forests
Stream Floodplain: These occur along major creeks or streams on low, flat terrain that regularly floods. Beech and loblolly are dominate and water oak, basket oak, willow oak, and laurel oak are typical. Loblolly pine and magnolia are present. The understory is normally open with some small trees or ironwood and American holly. Herbs are sparse dominated by grasses and sedges including cane. There is an absence of leaf litter due to winter flooding.
River Floodplain: They occur on the broad flats of the Neches River floodplain and tributaries of Beech Creek and Pine Island Bayou. Tree growth is rapid and many trees reach great size - - accentuated by the open understory. Dominate overstory species are basket oak, cherrybark, overcup, willow, and laurel oaks, and shellbark hickory. The dense midstory trees are ironwood and American holly. Vines are important here, more so than in other types. A large number of herbs are found on sandbars and in light gaps. Ground surface is usually devoid of leaf litter. Beech and magnolia are not present.
Cypress-Tupelo Swamp: These occur in deeper backwaters, sloughs, oxbows, and depressions. Both species form large buttresses and may reach large proportions. Edge species may be buttonbush, Carolina ash, water elm, and water hickory. Visit the Pine Island Bayou Unit to see this association type.
Flatland Forests
Flatland Hardwood Pine: This type is restricted to the Beaumont surface (geological formation) and is equivalent to the Lower Slope Hardwood Forests found elsewhere. It is restricted to the Lance Rosier Unit. The key to recognition is the absence of beech. White oak and southern red oak are dominate as are the magnolia, water oak, and loblolly pine. Some blackgum, laurel oak, and swamp hickory are present. Understory is dense with yaupon, American holly, horse sugar, and red bay. The herb layer is sparse.
Flatland Hardwood: These are also found in Beaumont formation, including the Lance Rosier Unit. These areas are found on low ground along creek drainage. Laurel oak and blackgum are the principal species. Basket oak, sweetgum, water oak, cherrybark oak, or willow oak are common. Shrubs include palmetto and arrowwood. Pines and sweetgum occur on small mounds. Red oak, white oak, and magnolia are absent.
Baygalls
These may occur within most any of the major types listed here; where water accumulates and stands for most of the year baygalls may form. Principal species are titi, gallberry holly, sweetbay, red bay, and blackgum. Other species may be present depending on the surrounding forest type including wax myrtle, white bay, horse sugar, and azalea. Ferns are common and include these species - - Christmas, cinnamon, and royal. Sphagnum, other mosses, and liverworts are found here as well.