Diversity and soil-tissue elemental relations of vascular plants of Callahan Mine, Brooksville, Maine, U.S.A.
Metal-contaminated soils provide numerous stressors to plant life, resulting in unique plant communities worldwide. The current study focuses on the vascular plants of Callahan Mine in Brooksville, ME, USA, a Superfund site contaminated with Cu, Zn, Pb, and other pollutants. One hundred and fifty-five taxa belonging to 50 families were identified, with the Asteraceae (21%), Poaceae (11%), and Rosaceae (9%) as the most species-rich families. Ninety-six species encountered at the Mine were native to North America (62%), including 11 taxa (7%) with rarity status in at least one New England state. Fifty-one species were non-native (33%), including nine taxa (6%) considered invasive in at least one New England state. We characterized how the plant community changed across different habitats at the Mine, from disturbed and exposed (waste rock piles, tailings pond) to inundated and relatively undisturbed (wetland, shore), and documented concurrent shifts in the ionic content of the soils across the habitats. We found substantial differences in both the plant community and soil chemical features among habitats. Habitats separated out along a single axis of an ordination of the plant community, with wetland and shore habitats at one extreme and tailings pond and waste rock-pile habitats at the other. The first principal component axis of the 21 soil variables was significantly predicted by the ordination of the plant community, indicating a gradient of increasing organic matter, Fe, Mg, Mn, total N, Na, and K roughly parallel to the gradient of increasing wetland vegetation. None of the plant species tested accumulated substantial concentrations of metals in their leaf tissue except Salix bebbiana and Populus balsamifera, which accumulated 1070 ppm and 969 ppm Zn in dry leaf tissue, respectively - approximately one-third of the concentration considered as hyperaccumulation for Zn.