74 Years of Ca loss from Forest Soils of the Adirondack Mountains, NY

In 2005/6, we conducted a remeasurement investigation of organic and mineral horizon Ca at 54 sites in forests of the Adirondack Mountains, New York. This network of plots represents northern hardwood, pine-dominated, and high-elevation spruce–fir stands typical of this region. Soil Ca had been measured at these sites twice (1930–1932 and 1984) in the previous 74 yr. Consistent with the original methods, we used measurements of dilute HCl (0.2 mol L−1) extractable Ca to make comparisons among the 1930 to 1932, 1984, and 2005/6 samples. Between 1932 and 2005/6, median HCl-extractable Ca content decreased significantly (78%) in organic horizons and in the whole profile (organic + mineral horizons, 64%), although significant decreases in mineral soil Ca content were confined to the upper 20 cm. Moreover, significant decreases in organic horizon (−1.5% yr−1), mineral horizon (−1.0% yr−1), and whole profile (−1.5% yr−1) Ca content between 1984 and 2005/6 indicated that Ca depletion has been sustained in recent decades. When stratified by forest type, there were significant decreases in extractable Ca concentrations and content in organic horizons and in the whole profile for all forest types between 1932 and 2005/6, although decreases between 1984 and 2005/6 were not necessarily significant. Overall, the rate of median whole-profile Ca depletion (∼13.6 kg ha−1 yr−1) was similar during all sampling intervals, suggesting that the combined Ca inputs from atmospheric deposition and mineral weathering have not kept pace with leaching and sequestration in biomass during much of the 20th and early 21st centuries in these plots