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The reactive form of Aluminum (Al) is mobilized from the mineral soil to the forest-floor soil due to acid deposition. This reactive Al reduces the availability of Calcium (Ca) present in the forest-floor soil to the plants. The Ca uptake by plants decrease as a consequence. The decrease of exchangeable Ca in the upper soil horizon is not accompanied by a change in exchangeable H or soil pH. Dissolution of mineral Al or decomplexation of organic Al are not responsible for the loss of Ca since these does not occur from acid deposition.

The depletion of root-available calcium in northern forests soils exposed to decades of increased acid deposition adversely affects forest health and productivity. Laboratory studies indicated the potential of wood-decay fungi to restore lost calcium to the rooting zone of trees. This study reports changes in concentrations of Ca, Mg, and K during decay of sapwood of spruce, maple, hemlock, and birch at two locations in northern New England, USA. Concentrations of exchangeable Ca, Mg, and Al in decayed wood residues after 10 and 12 years of ground contact were also compared. Significant loss of mass indicated by decreasing wood density occurred after two to eight years in conifers and after only two years in hardwoods. A significant gain in wood K was observed at two years, but the gain was not sustained. A significant gain in Ca concentration occurred by six years and that gain was sustained for 12 years. Concentrations of Mg varied. No significant difference in exchangeable Ca concentration was observed between decayed wood residue of spruce and maple and the forest floor. However, decayed wood residue had a much lower molar Al/Ca ratio, a conditional characteristic of sites with high root-available Ca. [ABSTRACT FROM AUTHOR]