People have called the Big Thicket an American ark and the biological crossroads of North America. The preserve was established to protect the remnant of its complex biological diversity. What is extraordinary is not the rarity or abundance of its life forms, but how many species coexist here. Once vast, this combination of pine and cypress forest, hardwood forest, meadow, and blackwater swamp is but a remnant. With such varied habitats, "Big Thicket" is a misnomer, but it seems appropriate. An exhausted settler wrote in 1835: "This day passed through the thickest woods I ever saw. It...surpasses any country for brush."

Major North American biological influences bump up against each other here: south eastern swamps, eastern forests, central plains, and southwest deserts. Bogs sit near arid sandhills. Eastern bluebirds nest near roadrunners. There are 85 tree species, more than 60 shrubs, and nearly 1,000 other flowering plants, including 26 ferns and allies, 20 orchids, and four of North America's five types of insect-eating plants. Nearly 186 kinds of birds live here or migrate through. Fifty reptile species include a small, rarely seen population of alligators. Amphibious frogs and toads abound.

Although Alabama-Coushatta Indians hunted the Big Thicket, they did not generally penetrate its deepest reaches, and the area was settled by whites relatively late. In the 1850s economic exploitation began with the cutting of pine and cypress. Sawmills followed, using railroads to move out large volumes of wood. Ancient forests were felled and replanted with non-native slash pine. Oil strikes around 1900 brought further forest encroachment. Nearby rice farmers flooded some forests; others were cleared for housing developments.

Designation of Big Thicket as a national preserve created a different management concept for the National Park Service. Preserve status prevents further timber harvesting but allows oil and gas exploration, hunting, and trapping to continue. In 2001 the American Bird Conservancy designated Big Thicket National Preserve a Globally Important Bird Area. The preserve is composed of 12 units comprising 105,684 acres, more or less. It was designated an International Biosphere Reserve by the United Nations in 1981. The protected area will provide a standard for measuring human impact on the environment.