Holocene Vegetation Dynamics of an Upper St. Lawrence River Wetland: Paleoecological Evidence for a Recent Increase in Cattail (Typha)

Cattails ( Typha latifolia L., Typha angustifolia L., and Typha x glauca Godr.) are the predominant emergent vegetation of upper St. Lawrence River coastal wetlands. We sought to describe Holocene vegetation in a St. Lawrence River wetland to assess patterns of succession and examine the timing and potential causes of a historic cattail invasion. Paleoecological analysis indicated presence of four distinct wetland vegetation stages, including a shallow water marsh (8240 YBP to 5160 YBP), a variable-depth aquatic plant community with adjacent alder (5160 YBP to 1610 YBP), a shallow sedge community (1610 YBP to 100 YBP), and a robust emergent marsh (100 YBP to present). The record of pollen tetrads demonstrated cattail presence throughout the history of the marsh, but a rapid increase in relative abundance of Typha cf. angustifolia/Sparganium monads indicated major expansion of robust emergent plants beginning near the peak of agricultural activity (ca. 1880 AD) and reaching modern levels around 1940 AD. Increase in the abundance of robust emergents in this wetland occurred decades before regulation of St. Lawrence River water levels and were contemporary with increased sedimentation and changes associated with the early agricultural period.