The chemical characteristics of soil in control and experimentally thinned plots in mesic oak forests along a historical deposition gradient

This study examined the variations in the chemical parameters of soils of seven forests located along a historical deposition gradient spanning 8.5 degrees longitude from southern Illinois to central West Virginia. Four to six mature control plots were sampled on two of the sites, and two experimentally thinned and two control plots were sampled on the remaining five sites. Most soil properties varied significantly both among experimental forests and between control and thinned plots. Soil pH, Al, PO4 and inorganic N were correlated with longitude, whereas differences in Ca, Mg and Ca:Al ratio among experimental forests were more closely linked to differences in parent materials. Nine of the 12 soil properties measured differed between control and thinned plots, and the variance explained by the proportion of basal area removed in the experimental thinnings was always greater than that explained by longitude or current basal area. Overall, thinned plots had greater soil pH, inorganic N, Ca, Mg, K and Ca:Al ratio, whereas control plots had greater Al and PO4. These patterns of difference were also apparent when the chemical properties of soil of the experimental forests were analyzed individually. We suggest that thinning may have reduced uptake, increased relative nutrient availability, changed leaf and litter quality, and altered decomposition and mineralization rates in such a way as to produce persistent differences in soil properties. (C) 1997 Elsevier Science B.V.