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Harvard Forest Symposium Abstract 2005

• Title: Long-term history of vegetation and fire in the pine barrens region of Long Island, New York
• Primary Author: Wyatt Oswald (Emerson College)
• Additional Authors: David Foster (Harvard University); Glenn Motzkin (University of Massachusetts - Amherst )
• Abstract:

  Forest management and conservation strategies often benefit from a long-term perspective, but little paleoecological or historical information is available for the pine barrens of central Long Island. This region of Pinus rigida-Quercus plant communities is of great ecological and conservation interest at present, as these communities provide habitat for a range of rare and endangered plant and animal species. Our understanding of past vegetation patterns and disturbance regimes in this region is based on a few poorly-dated paleoecological records and historical accounts and maps made after European settlement. Detailed reconstructions of past vegetation and fire are long overdue, as the origin of the pine barrens of Long Island has been debated for over a century. Some researchers attribute the presence of these communities to natural factors, including frequent disturbances and xeric, unproductive soils, while others see them as an artifact of anthropogenic activities, including land clearance and burning. Clearly, an improved understanding of the history of Long Island pine barrens communities would greatly inform forest conservation and management efforts. In addition, a long-term perspective would help us to better predict the future of the remaining pine barrens, as paleoecological data illustrate how past environmental changes affected patterns of vegetation and fire. To reconstruct the history of vegetation and fire in Long Island’s pine barrens, we analyzed pollen and charcoal in a 10,000-year sediment record from Wildwood Lake. These analyses indicate that forest composition and fire activity changed in response to climatic variability at various times in the past. From ~10,000-8200 years before present (BP), abundant Pediastrum algal cell nets indicate low lake levels, and thus dry climate, while relatively high values of Pinus and Quercus pollen and charcoal indicate pine/oak-dominated forest with frequent fires. From ~8200-5400 years BP, reduced Pediastrum, Pinus, and charcoal abundance and higher Quercus pollen percentages indicate wetter climate, reduced fire activity, and greater abundance of oak species relative to pine. At ~5400 years BP, Tsuga pollen percentages decline, but low percentage values before that time suggest that hemlock was relatively rare or absent. However, even though a dramatic Tsuga pollen decline was not observed, a variety of other changes indicate ecological changes in response to a climatic shift from ~5400-3000 years BP. Increased Pediastrum suggests drier climate, and higher percentages of Pinus, Betula, Carya, Acer, Fagus, and Castanea indicate substantial changes in forest composition. Tsuga pollen percentages recover at ~3000 years BP, Pinus pollen percentages increase (P. rigida-type in particular), and a drop in Pediastrum abundance suggests that climate became cooler at that time. That forest type persisted until ~300 years BP, when European settlement, land clearance, and agriculture began in central Long Island. Those changes are represented in the pollen data by declining tree pollen values and higher abundance of agricultural weeds (Rumex, Ambrosia, and Poaceae). Higher charcoal abundance reflects an increase in fire activity during the settlement period. Overall, the record from Wildwood Lake suggests (1) that the vegetation of central Long Island changed in response to past climatic variability, and (2) that pine barrens plant communities have been present in this area for the past ~3000 years, and thus are not likely an artifact of past land-use activities.

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