Postglacial and Interglacial Vegetation History of Southern Georgia and Central Florida.

Abstract

From 8,500 to 5,000 radiocarbon years ago three sites in southeastern Georgia and peninsular Florida, Lake Louise, Scott Lake, and Mud Lake, had predominant sclerophyllous oak forest, scrub, or savanna, probably with patches of bluestem prairie. About 5,000 year ago pine forest came to predominate on upland sites, and there was a more diverse flora of broad-leaved trees than before. Bayhead and cypress swamp vegetation did not become significant until after 5,000 BP, when Fagus (beech) also became abundant for the first time. The sediments at both Lake Louise and Scott Lake present evidence for recent forest clearance and consequent modification of the lake ecosystem. No vegetation record is available for the earlier postglacial or the period of the main Wisconsin Glaciation. Probably most lake basins of the region were dry during this time because of depression of the regional water table in highly permeable Tertiary limestones, caused by eustatic depression of sea level during Wisconsin Glaciation. At Lake Louise, as at Mud Lake, organic deposits too old to be dated by the radiocarbon method underlie the postglacial sequence, separated from it by clastic sediments that represent a large sedimentational hiatus. The lower organic deposits have the characteristics of an interglacial cycle. They are referred to the Sangamon interglacial, thus modifying a previous opinion that the Mud Lake sediments were partly Illinoian and partly Sangamon in age. A basic interglacial cycle proceeding from dry oak forest and herbaceous communities with eutrophic lakes to pine forest with hammock, bayhead, and cypress swamp vegetation is reconstructed for the southeastern United States.