This ecoregion ranges from southern Illionois, through much of Mississippi, east to Georgia, and west to Louisiana. This is the smallest ecoregion in Louisiana, and is restricted to the hills north of Baton Rouge, locally called the Tunica Hills. Although the Tunica Hills Ecoregion only covers about 120 square miles in Louisiana, it is one of the most diverse regions in our state. A unique set of geological and physical forces have shaped this region into a topographically complex landscape capable of supporting a myriad of species. Wind-deposited silt, called loess, was deposited on uplands along the east bank of the Mississippi River between periods of glaciation in the late Pleistocene and early Holocene epochs (10,000 to 80,000 years ago). A more-or-less continuous band of silty soils extends from southern Illinois to a point near present day Baton Rouge. This band of loess varies from 10 to 20 miles in width and reaches a depth of up to 200 feet. These silty deposits, as well as the underlying soils, are highly erodible, and the action of centuries of rainfall runoff has sculpted this region into a series of deep ravines, steep slopes, and narrow ridgetops.
Early land survey records indicate that the dominant trees in this region were American beech, southern magnolia, and American Holly, although many additional species of hardwood trees were also present. This habitat type is referred to as Southern Mesophytic Forest by plant ecologists. In Louisiana, this region is bounded by the Mississippi River on the west, the Louisiana/Mississippi border on the north, and Thompson Creek on the east and south. The plant community extends north to Vicksburg, Mississippi, the generally recognized northern limit of southern magnolia.
The relatively cool ravines in the Tunica Hills have produced a micro-climate that supports plant and animal species typical of more northerly regions like the Ozarks and Appalachians. The Tunica Hills provided a refuge for those species during glacial periods, and many have managed to persist to this day. The combination of southern flora and fauna, with the remnants of species typical of cool, temperate habitats, has created an extremely diverse assemblage of species.
Early land survey records in this region also indicated extensive clearing of the ridgetops and the presence of more gradual slopes between the early 1820's and the early 1850's. Eventually few forested ridges remained, and many native plants and animals disappeared from all but the steep slopes and deep ravines. The Tunica Hills became an important agricultural center, and many of the popular trading routes used to haul agricultural products to the steamboat docks along the Mississippi River are visible today. After the Civil War, many plantations in the region were abandoned, and natural succession resulted in the forests we see today. The Tunica Hills is a perfect example of nature's ability to recover from extensive disturbance.
The words of Dr. William Platt, Professor of Plant Biology at Louisiana State University, aptly describe the current condition of this biologically unique area. "While there are a few other areas in the southeast where some northern species co-occur with southern hardwood forest species (e.g., the Apalachicola River Bluffs in Florida), the loess bluffs of the Tunica Hills is the largest area where northern and southern species are intermixed. The size of the area is important; as the size of area of any given habitat increases, the number of and the sizes of the populations of species present increase. In all the south, only the Tunica Hills contains a large enough area of sufficiently complex topography to provide the variety of microhabitats necessary to maintain populations of a large number of both northern and southern forest species. In this respect, the loess bluff forests of the Tunica Hills region stand out as the most species-rich of all southern forests.
The forest we see in the Tunicas are dominated by many of the same species recorded by the early land surveyors, with a few notable exceptions. American holly, once a conspicuous component of the predisturbance forests, is now usually only observed as a shrub with specimens over 30 feet tall being uncommon. Loblolly pine, which was never noted during the surveys and is thought to have occurred no further west than the area around Thompson Creek, is now very common in these hills. Loblolly pine seeds are readily dispersed by the wind and animals, and the species rapidly colonizes abandoned fields. Finally, exotic species, most notably Japanese privet, which likely escaped from ornamental plantings around the original plantations, have invaded even the most remote portions of the Tunica Hills.
Although the current forest composition varies somewhat from pre-disturbance times, we believe that most, if not all, of the species of plants and animals native to the Tunica Hills region still exist, and proactive conservation efforts will ensure that they persist for generations to come.
The Conservancy strives to protect the most endangered plant and animal species as well as remaining high-quality examples of natural habitats that may support countless species of both common and rare plants and animals. The Tunica Hills support the threatened Louisiana black bear, the only Louisiana location for Webster's salamander and eastern chipmunk, and several excellent examples of beech-magnolia-holly forest.
Although the Tunicas only support a few species considered at risk from a global perspective, at least 25 state-rare plant species occur in the Tunica Hills of Louisiana and Mississippi. At least 10 species of plants are known in Louisiana only from the Tunica Hills, including the only known Louisiana locations of wild ginseng and Canada wild ginger. Thirteen state-rare animals are known to occur in the area, including Louisiana black bear, Webster's salamander, long-tailed weasel, Coopers Hawk, and Louisiana Waterthrush. This region also supports significant populations of uncommon animals like timber rattlesnakes, and many species of migratory birds, including the Yellow-billed Cuckoo, Wood Thrush and Great-crested Flycatcher, which are apparently declining throughout their range.
The Nature Conservancy, the Louisiana Natural Heritage Program, and the Louisiana Office of State Parks long ago recognized the importance of the Tunica Hills region. The largest protected sites in the Louisiana portion of the Tunica Hills are the Tunica Hills State Preservation Area (3,477 acres) and Port Hudson State Commemorative Area (899 acres), both managed by the Office of State Parks, and the Tunica Hills Wildlife Management Area (3,365 acres), managed by Wildlife and Fisheries. The core of Tunica Hills Wildlife Management area was initially acquired by TNC in 1991 and the Conservancy recently acquired a 425-acre addition that will be transferred to LDWF in spring 2001. In addition, the Nature Conservancy's 109-acre Mary Ann Brown Preserve has been developed into a popular hiking destination and serves as an important environmental education platform for countless school and scout groups each year.
Although the facilities vary from first class to primitive, there are numerous areas open to the public that afford visitors an opportunity to experience this unique region. The Tunica Hills Wildlife Management Area is only minimally developed and the spectacular scenery is worth some previsit planning (a Wild Louisiana Stamp or a hunting or fishing license is required). Port Hudson State Commemorative Area includes a series of well-maintained hiking trails, a large picnic area and an historical museum. The Mary Ann Brown Preserve includes a self-guided interpretive trail, two additional hiking trails and a pavilion and camping area for school and scout groups.