The Big Thicket[3] is the name given to a somewhat imprecise region of a heavily forested area of Southeast Texas in the United States. This area represents a portion of the mixed pine-hardwood forests or "Piney Woods" of the Southeast US.[4] The National Park Service established the Big Thicket National Preserve (BTNP) within the region in 1974 and it is recognized as a biosphere reserve by UNESCO. Although the diversity of animals in the area is high for a temperate zone with over 500 vertebrates, it is the complex mosaic of ecosystems and plant diversity that is particularly remarkable. Biologists have identified at least eight, and up to eleven, ecosystems in the Big Thicket area. More than 160 species of trees and shrubs, 800 herbs and vines, and 340 types of grasses are known to occur in the Big Thicket, and estimates as high as over 1000 flowering plant species and 200 trees and shrubs have been made, plus ferns, carnivorous plants, and more. The Big Thicket has historically been the most dense forest region in Texas.[5][6][7][8]
Native Americans are known to have lived and hunted in the area nomadically, but did not establish permanent settlements there before the Alabama–Coushatta settled in the northeast about 1780. Spanish explorers and missionaries generally avoided the area and routed their roads around it. Logging in the late 19th and 20th centuries dramatically reduced the forest concentration. Efforts to save the Big Thicket from the devastation of oil and lumber industries started as early as the 1920s with the founding of the East Texas Big Thicket Association by Richard Elmer Jackson.[6][9]
Conservatively the area occupies all of Hardin County, most of Polk, and Tyler Counties, and parts of Jasper, Liberty and San Jacinto Counties, including areas between the Neches River on the east, the Trinity River on the west, Pine Island Bayou on the south, to the higher elevations and older Eocene geological formations to the north. Broader interpretations have included the area between the Sabine River on the east and the San Jacinto River on the west including much of Montgomery, Newton, Trinity, and Walker Counties, as well.[6][10][11] Several attempts to define the boundaries of the Big Thicket have been made, including a biological survey in 1936 which included over 3,350,000 acres (13,600 km2) covering 14 counties.[12] A later botanical based study in 1972 included a region of over 2,000,000 acres (8,100 km2).[13] This same habitat extends into Louisiana and eastward.[14]
One's fondness for the area is hard to explain. It has no commanding peak or awesome gorge, no topographical feature of distinction. Its appeal is more subtle.
— Big Thicket Legacy, University of Texas Press, 1977
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Geology: The Big Thicket is notable for the unusually high diversity of plants concentrated in a relatively small area. A major factor enabling this diversity is an unusually high diversity of soils. The exposed surface soils are relatively recent, late Cenozoic Era, predominantly Miocene, Pliocene, Pleistocene, and Holocene Epoch formations. Other than some slight and uniform tilting, the strata are not greatly deformed. The strata were laid down in several cycles of glaciations and warmer interglacial interludes. Although glaciers never extended as far south as Texas, it was during these cold periods that enough water was frozen in polar regions to lower sea levels and the Big Thicket area was dry land well above sea level. Conversely, during the warmer interludes, enough ice melted to increase sea levels and submerge Southeast Texas in the sea. It was during those warmer periods of submersion that alluvial and delta deposits from the streams and rivers of the continent laid down the succession of strata, each new layer burying and compacting the previous. At some point there was an approximately 1% tilting of the layers. Some say it was caused by the rising of the Rocky Mountains,[15] while others say it was the weight of the successive deposits that eventually caused the Gulf of Mexico to subside.[11] The older Pliocene, Miocene, and Oligocene formations are exposed in the north (Polk, San Jacinto, and Tyler counties), while the more recent Quaternary Period formations are exposed in the south (Hardin and Liberty counties).[11][15][16]
Soils: The soils of the various formations at the surface have shifted and intermingled through erosion and other factors over time and can be locally quite complex. The Big Thicket contains a greater variety of soils than any area of comparable size in the United States. Sources vary, but from 50 to 100 soil types are said to occur in Hardin County alone.[6][11] The surface soils tend to be slightly to strongly acidic, and only occasionally neutral in much of the Big Thicket Basin. However, calcareous or alkaline soils do occur in the region, particularly along the Trinity River, in the Beaumont Formation to the south, the Fleming Formation to the north, and northern areas of the Willis Formation where the layer is thin and erosion and road cuts have exposed the Fleming Formation. Most plants are sensitive to soil pH levels (acidic, neutral, or alkaline) and many species will only grow in areas with a specific soil type.[6][11] Claude A. McLeod's study stated that the Big Thicket was "an edaphicmesophytic climax forest" – edaphic, meaning the soil is a greater influence on the plants than the climate, and mesophytic meaning a medium moisture level.[13]
Topography: The Big Thicket Basin has been described as shallow bowl or dish, tilted to one side, with the high rim on the interior north and low rim on the coastal south. Eastern and western rims consist of the low ridges that divide the Neches River and Sabine River drainages on the east and the Neches River and Trinity River drainages on the west. Elevations range from about 350 feet (110 m) in the north to 25–35 feet (7.6–10.7 m) in the south, dropping as low as 3 feet (1 m) at confluence of the Neches River and Pine Island Bayou. Northern regions are characterized by low gently rolling hills and well-formed drainage systems of streams and creeks in the landscape. The southern regions are comparatively flat, with poor drainage and support moderately extensive wetlands.[11][17]
Hydrology: Hardin, Tyler, western Jasper and southeast Polk counties are drained by the Neches River and its tributaries: Village Creek and its smaller tributaries (Beach, Theuvenins, Turkey, Hickory, Kimball, Big Sandy, and Cypress creeks) in the north; Pine Island Bayou and its smaller tributaries (Little Pine Island Bayou and Mayhaw Bayou) in the south. Eastern regions, including eastern Jasper and Newton counties, are drained by several relatively short creeks running into the Sabine River. Western regions including central Liberty, northeastern San Jacinto, northern Walker counties and southwest Polk County (via Kickapoo, Long King, and Menard creeks) are drained by the Trinity River. Areas farther west are drained by the San Jacinto River, with east and west forks. Additional wetlands are extensive, including innumerable nameless swamps, cypress sloughs, oxbow lakes, wetland savannas, and baygall bogs. Floodplains and bottomlands in the south, can retain surface water for days and weeks after rain. The Sabine and Neches rivers flow into Sabine Lake, a natural occurring brackish water estuary, just southeast of the Big Thicket. The other large lakes in the region were constructed in the decades following the Second World War, including B.A. Steinhagen Lake (1947–53) and Sam Rayburn Reservoir (1956–65) on the Neches River drainage, Lake Livingston (1966–69) on the Trinity River, Lake Houston (1953) and Lake Conroe (1970–73) on the San Jacinto River.[6][11]
Climate: The proximity to the Gulf of Mexico gives the region a climate of mild winters, hot summers, and high humidity most of the year. Average precipitation is 55 inches (140 cm) a year,[18] with northern areas receiving about 50 inches (130 cm), and southern areas receiving about 60 inches (150 cm). However, tropical storms and hurricanes can increase annual rainfall to over 100 inches (250 cm). Humidity stays well above 60% most of the time and exceeds 90% often. Winters are mild, with nighttime lows averaging 38–48 °F (3–9 °C) and daytime highs 55–65 °F (13–18 °C). Winter cold fronts can drop temperatures to freezing, but freezes rarely last for more than a few days, sometimes only hours, averaging about 20 mostly nonconsecutive days each year. Snow is rare, occurring only once every ten years or so. Summer temperatures are hot, with nighttime lows averaging 69–72 °F (21–22 °C) and daytime highs averaging 89–94 °F (32–34 °C). Temperatures exceed 90 °F (32 °C) about 110 days each year and days with temperatures above 95 °F (35 °C) and even above 100 °F (38 °C) are not uncommon. The high summer temperatures with high humidity levels can produce very high heat index numbers.[6][11][19]
Population: In 2010, the United States Census Bureau reported a population of 54,635 for Hardin County, with an average of 61.3 inhabitants per square mile (23.7/km2) in a county of 890.5 square miles (2,306 km2). The larger towns (and populations from 2010 census) in Hardin County are Kountze, the county seat (2,123), Lumberton (12,448), Silsbee (6,611), and Sour Lake (1,813). Smaller unincorporated communities in the Hardin County include Batson, Honey Island, Saratoga, Thicket, Village Mills, and Votaw.[20]
Tyler County had a total population of 21,766, with an average population of 23.5 inhabitants per square mile (9.1/km2) in 924.5 square miles (2,394 km2). The larger towns in Tyler County are Chester (312), Colmesneil (596), Warren (757), and Woodville, the county seat (2,586) with smaller unincorporated communities including Doucette, Fred, Rockland, and Spurger.
Polk County had a total population of 45,413, with an average of 43 inhabitants per square mile (17/km2) in an area of 1,057.1 square miles (2,738 km2) in 2010 including Livingston (5,335), the county seat and the largest town in the county.[20]
Larger towns and cities in the greater region include Beaumont, Jefferson County, located at the southeast corner of the Big Thicket area with a population of 118,296 and Liberty, Liberty County (8,397), on the southern edge of the Big Thicket area. Houston, Harris County, with a population of 2,320,268 (greater metropolitan area over 7,000,000) is one of the largest metropolitan areas in the US with its central, downtown area located 75 miles (121 km) by air southwest of the town of Kountze, Hardin County.[20]
Economy: Timber, oil and gas, and agriculture continue to be significant to the economy of the area. Many people commute to work in oil refineries and related industries in the Beaumont area. Other sources list industries providing significant employment in Hardin County as: educational, health and social services, construction, recreation, accommodation and food services, finance, insurance, real estate, and rental and leasing.[20][21]
It is my observation that the Thicket communicates best with solitary wanderers, but it also speaks to companionable spirits. An important trick on the trail is to shift one's focus from the big scene to the minuscule. Take your time, folks. The Big Thicket is not a hurry-place.
— Maxine Johnston, Foreword in Nature Lover's Guide to the Big Thicket[5]
On a larger scale of ecoregions of the United States, the Big Thicket is part of the Piney Woods.[22] The Big Thicket is located in the southwest of the Piney Woods and transitions into the Western Gulf coastal grasslands[23] immediately to the south. To the west are the Texas Blackland Prairies and East Central Texas forests[24] (a.k.a. post-oak savanna). Within the Big Thicket, a major component in the high diversity of plants and animals is the variety of ecosystems present in a relatively small area. The National Park Service identifies eight plant communities in Big Thicket National Preserve.[25] Some biologist and plant ecologists identify as many as nine, ten, or eleven ecosystems in the Big Thicket.[5][6][11] In nature these ecosystems are not always found in pure, large tracts of land, and often occur in intertwined and checkerboard mixes and ecotones, transitioning into one another. Ecosystems do not have universal standardized names. Many ecologist, botanist, zoologist and others have studied and classified ecosystems in the Big Thicket region (and elsewhere), defining and naming these communities as relevant to their own disciplines and studies.[26][5] Although the exact names, definitions, and boundaries might vary (subdivided, compounded, or overlapping), below are summaries of ten major ecosystems recognized by most who have studied and written about the Big Thicket, starting with higher elevations in the north, and in a generalized way, moving to lower elevations in the south.
Uplands (aka: longleaf pine-bluestem uplands;[6] dry upland forests;[27][26] longleaf pine uplands[5][11]) In its natural state, this ecosystem is often described as having a park-like appearance, with widely spaced pine and oak trees, and grasses growing in the partially shaded open areas. Longleaf pine-bluestem grass uplands are most extensive in northern areas, on higher elevation plateaus between streams and dry upper slopes, where the soils of the Catahoula, Fleming, Willis, and Bentley formations often have several feet of moderately coarse sand over an iron oxide clay or plinthite hardpan stratum. The permeable sands and topography provide good drainage in the uplands which are relatively dry. Smaller fragments of this type are also found throughout the south where higher ridges, hills, and knolls occur. Longleaf pine (Pinus palustris) is a common species in this ecosystem and one of the dominant trees along with shortleaf pine (Pinus echinata) and a variety of oaks (Quercus). Understory shrubs include flowering dogwood (Cornus florida) and American holly (Ilex opaca). Plant ecologist Geraldine Watson stated the U.S. Forest Service grass herbarium in Louisiana has over 200 species of grasses from this range and various bluestem grasses (Andropogon) are the dominant ground cover.[11] Wildflowers like purple pleat-leaf (Alophia drummondii) and bird-foot violet (Viola pedata) grow in the lighter, semi-shaded areas, while Texas Dutchman's-pipe (Aristolochia reticulata) and false foxglove (Aureolaria grandiflora) grow in the deeper shade. Streams flowing through these areas can support large stands of southern bracken fern (Pteridium aquilinum). Longleaf pine, bluestem grass, and many other plants in these areas are pyrophytic (adapted and resistant to wildfire), and wildfires are a critical factor in maintaining this ecosystem. Historically, naturally occurring fires would periodically eliminate non-pyrophytic plant species encroaching on this plant community. However, decades of fire suppression has allowed a wide mixture of species to invade and in time has turned many of the upland localities into beech-magnolia-loblolly slope forest or oak-hickory forest. Additionally, many areas clearcut for lumber have been replanted with rows of the faster growing, non-native slash pine (Pinus elliottii) eliminating much of the longleaf pine-bluestem grass uplands from Texas.[6][11][26]
