Holocene Vegetational Changes in the Tombigbee River Valley, Eastern Mississippi

Abstract

Stratigraphic studies of pollen from an oxbow on a Holocene terrace and from an upland swale near the Tombigbee River in eastern Mississippi provide a record of Holocene vegetational changes. From -11,000 to 7300 years B.P. the forests were dominated by oaks and hickories. Mesic forest species were common, at least locally. This suggests the existence of a significant moisture gradient between central Miss.-Ala. and the vicinity of Goshen Springs (Delcourt, 1980) in southern Alabama. Mesic taxa declined markedly beginning at about 9000 years B.P. Between 7300 and 3500 years B.P., water levels in the oxbow dropped. Regional forests were dominated by oak and hickory, and mesic taxa became uncommon. Nyssa was extremely common between 2400 and 500 years B.P.; this probably included black gum in the uplands and both black gum and tupelo gum in wet lowland sites. A regional increase in pine is evident beginning at about 2400 years B.P. This pine expansion is eventually associated with decreases in oak; hickory and Nyssa. We suggest that aboriginal land use and an increased frequency of fires caused the latter forest changes. An increase in Ambrosia in the uppermost levels marks European settlement. At this time cypress, wetland herbs and shrubs, and Orontium colonized the oxbow, perhaps because of generally higher water levels due to decreased evapotranspiration caused by land clearance.