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Foliar Nutrient Concentrations Related to Soil Sources across a Range of Sites in the Northeastern United StatesForest, Range & Wildland Soils S oil base cations have declined in soils in the northeastern United States in the 20th century (Likens et al., 1998) due to forest harvesting (Federer et al., 1989;Johnson et al., 1991) and acidic deposition (Likens et al., 1996). Reductions in exchangeable soil Ca and Mg have been associated with declines of sugar maple (Bailey et al., 2004;Juice et al., 2006), an economically and ecologically important species. Sugar maple is thought to have high Ca requirements (Fujinuma et al., 2005;Page et al., 2008) while other species, such as beech, are less sensitive to soil base cation status (Duchesne et al., 2005;Park and Yanai, 2009). Acid deposition has also increased the concentration of dissolved inorganic Al in soil, which is toxic to plants (Foy et al., 1978;Delhaize and Ryan, 1995). Diff erences in the responses of tree species to regional variation in soil conditions may provide clues as to which species will be most sensitive to continued soil acidifi cation and base cation depletion.Sources of nutrients to forest soils include atmospheric deposition and mineral weathering (e.g., Graustein and Armstrong, 1983). Apatite, a ubiquitous but trace mineral in parent material, has been shown to be disproportionately important as a source of Ca and P in young soils, because of its high weathering rate