|
  |
    |
Like the ecoregions to the east, broadleaf deciduous trees dominate the Central U.S. Mixed Hardwood Forests. This region receives less precipitation than the more coastal areas, however, so drought-resistant oak-hickory forests predominate here. While other forests in the United States and Canada have both oak and hickory, this region was once the only one where both species occurred in abundance over a large area. Much of the natural habitat in this ecoregion has now been destroyed by development and agriculture. Most of the areas covered by the Central U.S. Mixed Hardwood Forests is rolling, but some parts are nearly flat and the Ozark highlands reach approximately 1,000 m. Parts of Kentucky and Tennessee are marked by dissected plateaus and basins.
The Central U.S. Mixed Hardwoods ecoregion is among the richest in North America for herbaceous plants and shrubs, with 2,527 species (Kartesz, personal communication). The tree flora is less diverse, dominated by only a few species. The oak-hickory forest becomes more savanna-like in its northern reaches. In southern Illinois and Indiana, the forest forms a mosaic with prairie. Widepsread dominants are white oak (Quercus alba), red oak (Q. rubra), black oak (Q. velutina), bitternut hickory (Carya cordiformis), and shagbark hickory (C. ovata). Flowering dogwood (Cornus florida) often occurs in the understory, along with sassafras (Sassafras spp.) and hop hornbeam (Carpinus spp.). The shrub layer is distinct, often with evergreens, and wildflowers are common. Intact wetter sites feature American elm (Ulmus americana), tuliptree (Liriodendron tulipifera), and sweetgum (Liquidambar styraciflua).
Habitat Loss Only about one percent of the Central U.S. Hardwoods remains as intact habitat. The majority of the ecoregion has been heavily altered by human activity, particularly conversion to agriculture, short rotation silviculture, and pasture in some areas (e.g., bluegrass). Remaining Blocks of Habitat All the remaining blocks of habitat in this ecoregion are smaller than 1000 km2. The most important are:
Degree of Fragmentation Most of this ecoregion has been highly fragmented, so large predators have disappeared. The remaining habitat blocks have some degree of connectivity, but few corridors exist between blocks. Degraded corridors within the blocks may be restorable, though the focus should be on improving the integrity of large blocks. Degree of Protection Mammoth Cave, Edge of Appalachia, and parts of the Missouri Ozarks and the Tennessee Cedar Glades are the only blocks of habitat in the ecoregion to enjoy substantial protection. These areas do not adequately protect the habitats of the central U.S. hardwoods. Types and Severity of Threats Urban sprawl and agricultural conversion are the greatest conversion threats to the region. Invasion of exotic grasses, cave vandalism and overuse for recreation, fire suppression in fire-maintained systems, and loss of large ungulates (bison) are degrading the remaining natural habitats. Deer poaching continues to be a problem in Kentucky and Tennessee, and collection of wild herbs is ongoing across the region.
 Relationship to other classification schemes This ecoregion corresponds roughly to the southern half of Bailey’s Eastern Broadlead Forest (Continental) Province. The northern portion of Bailey’s Province should be distinguished on the basis of climate, vegetation types, and ecosystem dyanmics. Omernik classifies the Ozark Highlands as a separate ecoregion, while we believe these rightly belong with the central U.S. hardwoods. Prepared by: A. Weakley, R. Noss, E. Dinerstein, S. Robinson, J. Adams 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.
|
More Photos