White Pine (left) and Oak (right) pollen grains as seen through a microscope.
Data from a transect of four cores collected in the Makepeace Cedar Swamp, near Carver, Massachusetts, record past changes in deposition, vegetation, and water level. Time series of pollen data provide a 14,000 year record of regional and local vegetation development, a means for biostratigraphic correlation and dating, and information about changes in water level. Differences in records among cores in the basin show that water level decreased at least 1.5 meters (m) between ~10,800 and 9700 calendar years before present, (cal yr B.P.), after which sediment accumulation was slow and intermittent across the basin for about 1700 years. Between 8000 and 5600 cal yr B.P., water level rose ~2.0 m, after which possibly slow peat accumulation indicates a low stand about the time of the hemlock decline at 5300 + 200 cal yr B.P. Dry conditions may have continued after this, but by 3200 cal yr B.P., the onset of peat accumulation in shallow cores indicates that water level had risen to close to its highest postglacial level, where it is today. Peat has accumulated across the whole basin since 3200 cal yr B.P. Data from Makepeace and from the Pequot Cedar Swamp, near Ledyard, Connecticut, indicate an early Holocene dry interval in southern New England that began 11,500 years ago near the end of the Younger Dryas interval. The dry conditions prevailed between 10,800 and 8000 cal yr B.P. and coincide with the arrival and later rise to dominance of white pine trees both regionally and near the basins. Our results indicate a climatic cause for the Pine period on New England.
diagram for one of the cores taken at Makepeace Cedar Swamp, Massachusetts
This study documents nearly synchronous changes (+ 500 years) in the hydrologic balance of individual basins throughout southern New England and the regional vegetation composition (i.e. an increase in the abundance of white pine pollen within the mixed forest) that demonstrates a similar link between hydrologic change and changes in the structural and taxonomic composition in forested biomes of the Northeast. The closely associated changes in the moisture balance and the regional vegetation change provide a plausible explanation for the long recognized early Holocene maximum in abundance and spatial coverage of white pine throughout the area (Davis, 1969; Gaudreau and Webb, 1985; Jacobson et al., 1987). As conditions warmed and the regional hydrologic conditions became drier (as shown from the water level evidence within individual basins), the vegetation shifted from more boreal and less drought-tolerant spruce to more temperate and drought-tolerant white pine. Maps tracing this history for spruce, pine, oak, beech, birch, hemlock, and other taxa support the inference of dry conditions in New England , southern Quebec, and the Maritimes when white pine dominated throughout the region (Webb and Webb, 1988; Webb et al., 1993; Webb, 1992).
These changes are also potentially significant for deciphering the nature of the early Archaic archaeological record, 9500 to 8000 yr. B.P., in southern New England.This record is not well understood because few sites are known, and those that have remains are context-poor. However, the early Archaic period begins during the transition from spruce- to pine-dominated forests in southern New England, and archaeologists have invoked the dramatic environmental changes for this interval to explain the apparent scarcity of sites in southern New England. Prior to the early Archaic, the Younger Dryas oscillation coincides with the first appearance of humans (Paleo-Indians) in the northeast. The Paleo-Indian material assemblage is different than the later Archaic groups, highlighting adaptation to the changing vegetation and fauna of cold and then warm conditions. Our work shows that the change in vegetation from spruce- to pine-dominated forests was accompanied by a regional shift to drier conditions that may be this postulated 'dramatic environmental change'. Alternatively, our results substantiate the possibility that much of the early Holocene archaeological material in the Northeast lies submerged not only by higher sea level along the coast but also by higher water and peat levels in lake and mire basins further inland that persist today.
Coastal Studies Geoarchaeology Paleoclimates Vegetation Dynamics