A PRE-SETTLEMENT FLORA OF WHITE CLAY CREEK, PA

The pre-settlement floral composition of the northeastern United States has been studied through both pollen and seed assemblages. The geomorphology of this region was highly altered due to the construction of mill dams during European settlement. However, no studies have used leaf macrofossils to construct Holocene floral communities in this region and quantify the impact of European colonization on pre-settlement plant communities. Leaves were chosen because unlike seeds and nuts, they cannot be reworked therefore frequently represent a more local species assemblage. Additionally, they can often be identified to higher taxonomic resolution than pollen. This study aimed to identify leaf subfossils to better understand the impact of European settlement on floral communities in southeastern Pennsylvania. Approximately 300 to 500 Leaves and leaf fragments were collected from a stream cut of the eastern branch of White Clay Creek in Chester County, PA, cleaned using a series of acid and base washes and identified using leaf architecture characters. The hydric soil layer they were collected from was likely deposited between 3,000 and 500 years before present and three samples from varying depths within the hydric soil layer are being radiocarbon dated to accurately constrain the time of deposition. We found that the pre-settlement flora was primarily composed of wetland species including swamp maple (Acer rubrum), sycamore (Platanus occidentalis), multiple species of willow (Salix spp.) and species from the birch family (Betulaceae spp.). This community is in sharp contrast to the weedy and upland species that compose the modern site flora and indicates that through the alteration of sedimentation via mill dams, humans have greatly altered the wetland plant communities in this region.