PRELIMINARY CHARACTERIZATION OF A PRE-COLONIAL RIPARIAN FOREST USING SUB-FOSSIL LEAVES FROM LITTLE CONESTOGA CREEK, SOUTHEASTERN PENNSYLVANIA

Reconstruction of a Piedmont wetland and adjacent hillslope plant community using sub-fossil leaves from Lancaster County, PA shows a significant shift in stream bank vegetation since colonial settlement. Leaf mat deposits occur within an organic-rich hydric soil immediately underlying remnant "legacy sediments" derived from colonial agricultural practices beginning in the 18th century. Between one and five meters of these silty sediments accumulated in slackwater ponds behind milldams, thus entombing the hydric soil, contributing to the loss of the natural floodplain, and causing subsequent vegetation shifts. Because leaves in fine-grained sediments are rarely deposited far from their source, the sub-fossil leaves presumably represent the woody plant taxa originally associated with these pre-colonial stream profiles, before the alteration of stream channel patterns from anabranching systems with adjacent hillslopes to the “riffle and pool” meanders observed today. Specimens were collected from Denlinger’s Mill on Little Conestoga Creek, part of the larger Susquehanna watershed. Blocks of hydric soil were removed, and leaf remains were separated from mud using alternating baths of HCl and KOH until most siliciclastic and organic matter was eliminated. Specimens were then mounted on glass slides and examined using fluorescence microscopy. Many specimens are identifiable to species based on leaf morphology, vein architecture, and cuticle features such as trichome types and stomatal configuration. Preliminary data indicate wetland and facultative non-wetland species presumed to be derived from the adjacent hillslope, including an abundance of Quercus spp. (oaks), Fagus grandifolia (American Beech), and various family Betulaceae (birches). This initial suggestion of a mesic mixed hardwood forest contrasts with the secondary forest observed adjacent to the creek today. Efforts will be continued to accurately constrain the original community and ecosystem type of this area, eventually leading to more effective stream restoration and conservation efforts in the future.