Nutrient ion exchange was examined between simulated acid rain solutions and northern red oak (Ouercus rubra L.) leaves of trees growing in fertile, limestone-derived soil and less fertile, sandstone/shale-derived soil. Leaves harvested from trees growing on the fertile site had greater concentrations of total N, P, K, Ca, and Mn but less total Mg than leaves of trees on the less fertile site. Cation losses from leaves of both sites were similar when exposed T3 to simulated rain solutions of pH 5.6, 4.3, and 3.0. Simulated rain solutions of pH 3.0 leached the greatest amount of total cations from leaves of both sites. Differences in acidity between leachates and starting rain solutions increased as the acidity of starting solutions contacting leaves of either site increased. Differences in leaf nutrient status between sites typically did not affect leachate acidity. Hydrogen ion exchange, believed to be the main mechanism of cation loss from leaves of both sites, accounted for 30 to 44% of all cations leached from leaves of both sites. Concentrations of inorganic ions were measured in bulk rainfall and bulk throughfall collected beneath northern red oak trees growing on the fertile and less fertile sites. Rainfall passing through crowns at both sites was enriched with S0₄²⁻, P0₄³⁻, Ca²⁺, Mg²⁺, K⁺, Mn²⁺, and Fe²⁺, but lost NH₄⁺ to the crowns. There was little difference in the inorganic chemistry of incident rainfall between sites. Large-particle dryfall ionic concentrations, rainfall volume, and leaf area were all larger at the fertile than at the less fertile site. Higher concentrations of Ca²⁺, Mg²⁺, NH₄⁺, Mn²⁺, and S0₄²⁻in throughfall at the fertile site compared to that of the less fertile site are likely due to the combination of these three factors. Historical northern red oak crown areas were estimated for the fertile and less fertile sites by a two step procedure using annual growth ring chronologies and published regression equations. These equations related total crown area to total crown dry weight. The usefulness of crown area estimates in throughfall studies was demonstrated by applying nutrient ion exchange data, collected beneath northern red oak crowns in 1984, to 1982 and 1930 crown area estimates. Smaller nutrient ion exchange estimates in 1930 were due to smaller crown area estimates. / Ph. D.