Late Quaternary Vegetation of Central Appalachia and the New Jersey Coastal Plain

Abstract

Pollen and plant macrofossil studies at 11 sites in New Jersey, southern and eastern Pennsylvania, West Virginia, and Virginia, USA reveal the character of the stable vegetation of the unglaciated eastern United States while the Wisconsin ice sheet was still at its outer limit. Grass—dominated tundra with dwarf shrubs was present 60 km south of the ice front at Longswamp, Pennsylvania. Sedge tundra covered the higher mountains of central Appalachia. In southern Pennsylvania, New Jersey (including the Pine Barrens), and northern Virginia, Picea (black or white spruce) was common, with Betula glandulosa (dwarf birch) and tall herbs, especially Sanguisorba canadensis (burnet). This is interpreted as forest tundra. In North and South Carolina and in northwest Georgia, forests of Picea and Pinus banksiana (jack pine) were present, with few deciduous trees. No site is yet known where broad—leaved trees formed the predominant vegetation cover anywhere on the Coastal Plain or in the Florida peninsula. With climatic warming, dwarf birch and spruce expanded into the tundra in unglaciated Pennsylvania. At Crider's Pond in southern Pennsylvania a Picea/Betula glandulosa assemblage with tall herbs was present from 15 000 to 13 000 yr BP. The associated aquatic flora was species poor. About 13 000 yr BP Abies balsamea (fir), Pinus banksiana, and Alnus cf. rugosa (speckled alder) invaded, together with diverse tree and shrub species, an assemblage like the southern boreal forest today. Betula populifolia (grey birch) occurs in this assemblage at Longswamp; there the aquatic flora is species rich. The increase in species diversity is evidence of marked climatic warming about 13 000 yr BP in southern and eastern Pennsylvania. Picea rubens (red spruce) arrived at Crider's Pond shortly before 11 500 yr BP, followed soon after by Pinus strobus (white pine). At Tannersville in glaciated eastern Pennsylvania an invasion series Picea—Abies—Pinus banksiana—Betula papyrifera (paper birch)—Larix laricina (tamarack)—Pinus strobus—Betula populifolia—Pinus rigida (pitch pine) can be demonstrated between 13 000 and 9000 yr BP. The stable flora of the periglacial region was different from the pioneer flora of the deglaciated area and from the vegetation of the modern tundra. As the ice withdrew, Tsuga (hemlock) and other tree species for which there is little or no fossil record at the height of the glaciation appeared in large populations in central Appalachia and the northern coastal plain, from which they invaded the deglaciated region at different rates. Castanea (chestnut), a slow migrant, took 5000 yr to reach southern New England from central Appalachia. Persistent tundra made the higher mountains of central Appalachia an important phytogeographical barrier to tree migration until about 12 500 yr BP. It explains differences in forest history west and east of the mountains. Tamarack seems to have migrated eastward from a glacial refuge south of the Great Lakes region. The distinctive modern vegetation of the Pine Barrens was assembled after about 10 000 yr BP. Climatically the periglacial region was cold, dry, and windy. The early Holocene from 10 000 to 6000 yr BP was warmer and drier than now, although not so dry as the Late Wisconsin. It can be identified as the Hypsithermal Interval. The subsequent expansion of Pinus may be attributed to a wetter climate, which caused increased bog and swamp formation and possibly also replacement of deciduous trees by pines as storm and fire frequency increased and soils were progressively leached of nutrients.