Covering approximately 82,000 mostly forested acres, the Cat Island-Tunica Hills complex includes Cat Island, a peninsular bottomland bordered on the north, west and south by an expansive bend in the Mississippi River, and a portion of the Tunica Hills, uplands adjacent to Cat Island on the east. The complex supports a small population of Louisiana black bear, a subspecies of the American black bear listed as threatened by the U.S. Fish and Wildlife Service.
Cat Island is the southernmost portion of the historic floodplain of the Mississippi that was not separated from the river by levees. Thus, the site retains much of its natural hydrology and floods during winter and spring most years to varying depths that may exceed 10 feet.
The "island," which has been designated a priority bird conservation area, shelters a suite of birds including Swainson's warbler, summer tanager and wood thrush that require large blocks of forest—at least 20,000 acres or more—to nest successfully. It is home to the national champion bald cypress tree and hundreds of other bald cypresses estimated at 500 to 1,000 years old.
The adjoining Tunica Hills were formed by the deposition of loess (wind-deposited soil). They are part of a band of such soils that extend more or less continuously as bluffs along the east bank of the Mississippi from southern Illinois to near Baton Rouge, Louisiana. Highly susceptible to erosion, the soils have been sculpted into a landscape of ridges with narrow tops, deep ravines and steep slopes. The ravines' cooler microclimate provides habitat for plant and animal species typical of more northern areas such as the Ozark and Appalachian mountains, which, in combination with occurring southern species, makes the Tunica Hills an ecoregion of significant biodiversity.
A significant portion of the forested land within the complex has been managed over the decades for timber production, and the composition and structure of these forests has been altered to some extent. In addition, some marginal agricultural lands within the site appear optimal for reforestation through incentive-based programs benefiting landowners.
Since 2000, The Nature Conservancy has purchased approximately 10,500 acres and partnered with the U.S. Fish and Wildlife Service to create Cat Island National Wildlife Refuge. Most of the Conservancy's land was transferred to the Service and incorporated into the refuge, and the Conservancy is continually working with willing landowners to acquire strategically important parcels to expand the refuge. The refuge acquisition boundary, approved by Congress, encompasses 36,500 acres.
In 1991, the Conservancy acquired the core area of what would become the Tunica Hills Wildlife Management Area, now totaling some 5,900 acres and managed by the Louisiana Department of Wildlife and Fisheries; the 110-acre Mary Ann Brown Preserve was also donated to the Conservancy that same year. Other publicly owned sites within the Tunica Hills are the Tunica Hills State Preservation Area (3,477 acres) and the Port Hudson State Commemorative Area (899 acres), both managed by the Louisiana Office of State Parks.