A 200-year paleoecological record of Pinus virginiana, trace metals, sedimentation and mining disturbance in a Maryland serpentine barren

The objective of this study was to provide stratigraphic data that could augment historic and recent ecological information concerning the cause of the 20th century vegetation shift from grassland to pine forest in a central Maryland serpentine barren, and potentially elucidate the role of fire, chromium mining, grazing, and other disturbances on serpentine vegetation. A 46-cm core was extracted from a shallow pond draining the watershed of Chimney Branch, underlain by serpentinite. Core chronostratigraphy was established by identifying two sharp spikes in Cr concentrations correlated with historic Cr mining activity peaks and an abrupt increase in pine needle abundance, when pine populations expanded around the coring site. Pine needle analysis reveals that Pinus virginiana (Virginia pine) has been present within a few meters of the coring site since ca. 1810, 120 years earlier than previously documented. A dearth of charcoal over the 200-yr period indicates there were no major fires at the coring site after 1820, although small ground fires within a few 10s of meters cannot be precluded. Mean sedimentation rates between dated horizons reveal that sediment efflux was highest during the early to mid-19th century (0.51–0.35 cm yr−1), synchronous with active Cr mining activity, and lowest in the past 50 years (0.19 cm yr−1) when the area fell under state management and pine forest expanded. Metal concentrations were highest for Cr and Ni, followed in decreasing order by V, Zn, Cu, and Pb. Results from this study suggest that 1) while Pinus virginiana was present in the early 1800s in sheltered lowland sites chromite-mining and its erosive effects on soil development may have been a factor in suppressing pine expansion in the Chimney Branch watershed between 1820 and 1920. Hence, pine expansion may be a natural stage in the succession of serpentine vegetation related directly to increasing soil depth, with the pace of expansion influenced by fire or mining disturbance; and 2) variation in Cr concentrations combined with mining history and macrofossils, in conjunction with aerial photos and recent studies, can provide useful stratigraphic dates to establish ecosystem development within the past 200 years in a serpentine environment.