Effects of European settlement and land use on regional patterns of similarity among Chesapeake forests

The changing composition and pattern of forests surrounding the Chesapeake Bay are the result of the historical interaction of natural processes and human influences. European settlement in the 17th century and the subsequent incorporation of the Chesapeake into a world economy changed the landscape of the Chesapeake Bay region. In this paper I examine the effects of European land-use practices on the forests surrounding the Chesapeake, by analyzing the record of pollen deposited in estuarine sediments during the last 1300 years. I analyze the patterns of species change and changes in the similarity of the ecological communities at three sites: The Nanticoke River, Magothy River and Furnace Bay. The effects of European settlement were not uniform. In some cases European settlement accentuated differences among sites, while in other cases, settlement diminished these differences and led to a homogenization of the plant communities. The variations seen in the effect of European settlement on the pattern of inter-site similarity depended on the nature of the original plant communities, the specific cultivation practices at the site, and the scale at which the plant communities were examined. At the scale of the entire pollen assemblage, incorporating patterns of forest and non-forest patches, the communities all became more similar to each other. Land clearance for agriculture or charcoal production imposed a similar physical structure on the landscape, one of fragmented forest patches and clearings at all of the sites. This physical structure was manifested in increasing dominance by disturbance-adapted species such as Ambrosia and a decrease in arboreal species such as Quercus and Carya. At the scale of the arboreal pollen, reflecting changes in the remaining forests, areas under the same pattern of land-use showed increased similarity while areas under different land-use showed less. Settlers intensively cultivated tobacco in the Magothy and Nanticoke River sites. The patterns of land-use under this crop system led to an increase in Pinus in the forest patches. The Magothy River site, formerly with low Pinus dominance, became dominated by Pinus and more closely resembled the Nanticoke River site. In contrast, Pinus dominance decreased in Furnace Bay, a region dominated by charcoal production.