Today there is very little intact habitat in this ecoregion, with a reduction of bottomland hardwood forests by 70-95%, and only 0.02 percent of the original oak savannas remain. Although much of the area is forested, these forests tend to be highly fragmented and significantly altered by development, agriculture, and fire suppression. The forests are dominated primarily by oak and hickory species, but succession has filled the understory with maples and yellow poplar and blocking oak regeneration. In some areas, habitat is threatened by urbanization and invasive species such as non-native privet, honeysuckle, garlic mustard and kudzu. Significant natural areas in the ecoregion include: Wolf River (Tennessee), the Cedar glades and the western Highland Rim of Tennessee; Mammoth Cave National Park; the Land Between the Lakes National Recreation Area of Tennessee and Kentucky; Hoosier National Forest and Yellowwood State Forest in southern Indiana; the Edge of Appalachia Preserve in Ohio; the Cache River (Illinois) wetlands and the Shawnee Hills in southern Illinois; and the Ozarks in Missouri including Mark Twain National Forest. The best preserved of these are Mammoth Cave, Edge of Appalachia, and parts of the Missouri Ozarks and the Tennessee Cedar Glades.