A 12 000‐Year Record of Forest History form Cahaba Pond, St. Clair County, Alabama

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Abstract
A 650—cm sediment sequence from Cahaba Pond, St. Clair County, Alabama spans the past 12 000 yr and has yielded a pollen and plant—macrofossil record indicating major changes in forest composition during the Holocene interglacial. Both pollen and plant macrofossils from sediments of this 0.2—ha pond primarily reflect changes in local and extralocal forests within the surrounding watershed. Four distinct pollen assemblage zones were recognized: a Fagus—Ostrya zone from 12 000 to 10 200 BP, a Pinus—Magnolia zone from 10 200 to 10 000 BP, a Quercus—Carya zone from 10 000 to 8400 BP, and a Nyssa—Pinus zone from 84 BP to the present. Forests of the early Holocene (12 000 to 10 000 BP) were mesic and predominantly composed of broadleaved deciduous trees, dominated by beech (Fagus grandifolia) and with substantial representation of hornbeam (Ostrya/Carpinus), oak (Quercus), hickory (Carya), elm (Ulmus), and ash (Fraxinus). Atlantic white cedar (Chamaecyparis thyoides), today a coastal species, extended inland to St. Clair County during the early Holocene. Eastern white pine (Pinus strobus), hemlock (Tsuga), striped maple (Acer pensylvanicum), and mountain maple (Acer spicatum), today rare or absent in Alabama, extended southward of their present ranges into central Alabama 10 000 yr ago. Outliers of mixed, mesic hardwood communities in the southern Ridge and Valley and Piedmont provinces may be relicts that date from the early Holocene, a time with high species richness and equable climate. After 10 000 BP, forests became more xeric, with oaks and hickories predominant. Cahaba Pond, formerly dominated by submersed aquatics such as Najas gracillima, became shallower, and floating—leaved and emergent aquatics became abundant. A decrease in effective precipitation is inferred for the time period between 10 0000 and 8400 BP. After 8400 BP, black gum (Nyssa sylvatica), southern pines (Diploxylon Pinus), red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), buttonbush (Cephalanthus occidentalis), and other elements of the modern flora became established locally. Water levels in the pond became higher, and sedimentation rate diminished, as observed in other pond sites in the region. An increase in effective precipitation in the late Holocene reflects the establishment of the modern atmospheric circulation patterns, including increased frequency of hurricanes developing in the Gulf of Mexico and the equatorial Atlantic Ocean.