Dynamism in the Barrier‐Beach Vegetation of Great South Beach, New York

Pollen data were used to reconstruct the past 340 yr of vegetational changes at Great South Beach, a system of barrier beaches east of Fire Island Inlet, Long Island, New York. The data came from cores taken along 16 transects, 6 of which are described in detail. Dates and stratigraphy from individual cores provided local environmental histories that were combined to reconstruct temporal and spatial patterns of vegetation on local and regional scales. Changes in inlet status and local disturbances accounted for much of the dynamism in vegetation. Salt marshes fringed back—barrier lagoons only when many inlets were open and saline conditions prevailed (1760 to 1835; 1931 to the present). Cyperaceae dominated marshes throughout the remainder of postsettlement time. Inlets affected vegetation by altering tidal range and salinity in back barrier lagoons and provided new substrates for marsh establishment when flood—tide deltas were abandoned by inlet channels. At least once every 100 yr along the six transects, sufficient sand was deposited to destroy all vegetation. The composition of invading assemblages on primary substrates was regulated mainly by physical factors. Annual herbs, shrubs, or high—marsh plants each were "pioneers" at different localities and times. Putative "pioneer" annuals were not limited to the early stages of succession. Fluctuating water tables played an important role in determining composition of freshwater wetlands. Biotically controlled trends in plant composition could not be positively identified. The reconstructions on Great South Beach indicate tight environmental control of plant distribution but emphasize that vegetation does not achieve an equilibrium with the physical environment. Present distributions are largely the product of historical events acting together with existing conditions.