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The Southeastern Mixed Forests skirt the Appalachian/Blue Ridge Mountains, occupying the piedmont zone between upland forests and the Atlantic Coastal and Gulf Coastal plains. This ecoregion is by far the largest within the Temperate Broadleaf and Mixed Forests MHT, crossing nine states and running northeast to southwest from Maryland to Louisiana. The Southeastern Mixed Forests are demarcated from the Southeastern Conifer Forests to the south by vegetation (Küchler 1985) and elevation (the fall line of the Atlantic piedmont). The latter ecoregion is more dominated by long-leaf pine (Pinus palustris) and occurs on the coastal plain rather than on the piedmont. It is similarly separated from the Appalachian/Blue Ridge Forests [NA0403] and Appalachian Mixed Mesophytic forests [NA0402] by elevation and vegetation. The Southeastern Mixed Forests, lying between all of these species-rich ecoregions, is enriched by the proximity to these other units. However, this ecoregion is perhaps the most heavily altered, having been heavily and repeatedly logged and now largely converted to agriculture.
The Southeastern Mixed Forests are famous as the center of gastropod diversity for North America and perhaps the world, but many of the endemic taxa are extinct. The freshwater ecosystems found within this ecoregion are among the richest in the temperate latitudes. The Southeastern Mixed Forests rank among the top ten ecoregions in richness of amphibians, reptiles, and birds and among the top ten ecoregions in number of endemic reptiles, amphibians, butterflies, and mammals. Kartesz lists 3,635 species of native herbaceous and shrub species, the highest in North America. The natural vegetation is dominated by oak-hickory-pine forests (Küchler 1964). At the time of European settlement this ecoregion was dominated by stands of pure pines and stands of pure hardwoods, with mixtures of each between these extemes. Hardwoods were much more prevalent in distribution than they are today (Skeen et al. 1993). The most dominant ecological force in shaping compostion and structure of the Southeastern Mixed Forests, prior to European settlement, was fire. Fire disturbance provided good seed beds for pines, and consequently maintained pine stands. Low-intensity frequent fires in hardwood stands favored oak regeneration over competing hardwoods. With European settlement of the ecoregion, the natural vegetation pattern was significantly altered, as forests were converted to shifting agriculture. After World War II, many of these farms were abandoned. Pines outcompeted hardwoods for sun and nutrients, and survived better in the extreme environmental conditions of the abandoned fields. Common pine species of this ecoregion include shortleaf pine (Pinus echinata), loblolly pine (Pinus taeda), and longleaf pine (Pinus palustris). Hardwood species grew in after the pines and established themselves prominently in the understory. Since the mid 1960's pine stands have been harvested, and hardwoods stands have taken their place, outcompeting juvenile pines for dominance in the overstory. In addition, the suppression of natural fire regimes has shifted vegetation to hardwood forests. This unnatural management practice has altered the plant communities across the ecoregion and threatens the long-term persistence of many fire-dependent species. The understory and herbaceous layers of the ecoregion follow similar successional gradients. On open fields with high light, grasses and forbs dominate. As pines and hardwood tree species overtop them and the canopy begins to close, more shrubs and small tress fill in. They include small tree species such as dogwood (Cornus spp.), red bud (Cercis canandensis), cedar (Juniperus spp.), and American holly (Ilex opaca). Common shrubs and herbaceous species include blackberry (Rubus spp.), sumac (Rhus spp.), honeysuckle (Lonicera spp.), and poison ivy (Toxicodendron radicans) (Skeen et al. 1993). Habitat Loss About 99 percent of this habitat has now been converted to agriculture or other uses, or is highly degraded. Habitat loss is relatively uniform across the ecoregion. This is the most heavily settled ecoregion along the east coast of the U.S., and much of the land has been used for growing tobacco and peanuts. The once dense forests harvested long ago have never been allowed to regrow to a mature age. There are large amounts of tertiary forests that offer little biodiversity value. A remnant tallgrass prairie, the so-called Black Belt, has been completely converted. A few habitats are in relatively good condition, particularly on granite outcrops. Remaining Blocks of Intact Habitat Nine blocks of habitat have been identified by this analysis, but most are in relatively poor condition, fragmented, and poorly protected. These include:
Degree of Fragmentation Fragmentation is very high and creation of new corridors is unlikely except in riparian areas. The species most susceptible to fragmentation, such as black bears (Ursus americanus), have been largely extirpated. Degree of Protection Poor, as stated above. Types and Severity of Threats Because of the heavy rate of conversion, there is little left to conserve. Logging remains a threat, as does continued exploitation of remaining forests, and conversion to pine plantations. The lack of fire management in remaining areas is viewed as a serious degradation threat.
 Relationship to other classification schemes The Southeastern Mixed Forests corresponds to the eastern piedmont and southwestern portions of Küchler’s (1975) unit 101 (oak-hickory pine forest) east of the Mississippi River. In addition, this ecoregion contains unit 80 (Blackbelt). This ecoregion is in large part a combination of Omernik’s (1995) unit 65 (Southeastern plains), portions of unit 74 (Mississippi Valley loess plains), and disjunct unit 68 (Southwestern Appalachians). Several portions of Bailey’s (1994) sections 231A (Southern Appalachian piedmont), 231B (Middle coastal plains), and the northern section of 232A (Middle Atlantic coastal plain) correspond to this ecoregion. Prepared by: A. Weakley, E. Dinerstein, R. Noss, K. Wolfe. This text was originally published in the book Terrestrial ecoregions of North America: a conservation assessment from Island Press. This assessment offers an in-depth analysis of the biodiversity and conservation status of North America's ecoregions. All text by World Wildlife Fund © 2001 For more general information on this ecoregion, go to the WildWorld version of this description.
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