Vegetation change during the past 25 000 years in and near the present Mixed Mesophytic Forest Region is inferred from pollen and plant macrofossil analyses of sediment cores from two sites on the eastern Highland Rim of Middle Tennessee, USA. Anderson Pond, in White County, dates from 25 000 radiocarbon years BP to present. During the Farmdalian Interstadial, 25 000 yr BP, northern Diploxylon pines, spruce, and deciduous trees were present at Anderson Pond, indicating a cool, moist climate. From 19 000 to 16 300 yr BP, during the Late Wisconsin glacial maximum, boreal taxa of jack pine, spruce, and fir were dominant. Late—glacial climatic amelioration began in Middle Tennessee at about 16 300 yr BP, with replacement of jack pine—spruce—fir forest by deciduous forest. Ash, ironwood, hickory, birch, butternut, willow, and elm increased in importance first, followed by beech and sugar maple. Mixed mesophytic forest taxa were most abundant during the early Holocene, between 12 500 and 8000 yr BP. A warming and drying trend between 8000 and 5000 yr BP is reflected by high influx values for pollen of oak, ash, hickory, swamp alder, and buttonbush, and by diminishing importance of mixed mesophytic forest taxa. Mingo Pond, Franklin County, Tennessee, contains a pollen record estimated to extend back to 14 000 yr BP. Mixed mesophytic forest taxa were abundantly represented at Mingo Pond during the late glacial and early Holocene, along with pollen representing prairie vegetation. Oak and sweetgum dominated the mid— and late Holocene record from Mingo Pond. Stratigraphic sites from the Missouri Ozarks to the Atlantic Coastal Plain date the full glacial in the southeastern United States between 23 000 and 16 500 yr BP. During the glacial maximum, boreal—like coniferous forests of spruce, jack pine, and fir extended southward to 34°N latitude. Mesic deciduous forest persisted through the full glacial at 35°N at Nonconnah Creek near Memphis. Full—glacial refuges for deciduous forest species may have also existed in south—facing gorges of the Cumberland Plateau and southern Appalachian Mountains in addition to bluffs along major streams in the southeastern United States. During the late glacial, beginning about 16 500 yr BP, boreal—like coniferous forest was replaced in midlatitudes (34° to 37°N) by cool—temperate coniferous—deciduous forest. In the early Holocene, between 12 500 and 8000 yr BP, cool—temperate mixed mesophytic forest prevailed between 34° and 37°N. The Mixed Mesophytic Forest Region assumed its present distribution in the mid—Holocene.
