The Effects of Leaching and Whole-Tree Harvesting on Cation Budgets of Several Forests

The effects of acid deposition, natural leaching, and harvesting on base cation export from forests in Maine, Tennessee, South Carolina, North Carolina, and Washington were compared. Based on previous literature, we hypothesized that base cation export via whole-tree harvesting (WTH) would be nearly independent of soil exchangeable base cation supplies; base cation export via leaching would be strongly dependent on the exchangeable cation supplies as well as the input, production, and mobility of anions. This hypothesis was supported by the data: mixed deciduous sites in Tennessee had among the highest base cation (principally Ca) exports via WTH (1.2 kmolc ha–1 yr–1), yet the lowest soil exchangeable supplies (35 kmolc ha–1), whereas the Washington sites had by far the highest base cation leaching (5–41 kmolc ha–1 yr–1, due to very high levels of naturally produced HCO–3) and soil exchangeable supplies, yet only relatively moderate base cation exports via WTH (0.4 kmolc ha–1 yr–1). Sulfate was either the dominant or a major anion in soil solutions from the eastern sites, suggesting that atmospheric deposition was a major factor in soil leaching from these sites (0.2–2.1 kmolc ha–1 yr–1), but total leaching rates from these sites were much lower than at the Washington sites. Indeed, some of the eastern sites showed a net annual accumulation of one or more base cations from atmospheric deposition. Some of the southeastern sites with Ultisols showed the expected net retention of SO2–4, but the sites in the Tennessee Valley near Oak Ridge showed surprisingly little ecosystem SO2–4 retention, perhaps due to lower soil SO2–4 adsorption in these soils than in other Ultisols