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 spann ing 8.5 degrees longitude from southern Illinois to central West Virgi nia. 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 b oth among experimental forests and between control and thinned plots. Soil pH, Al, PO4 and inorganic N were correlated with longitude, where as differences in Ca, Mg and Ca:Al ratio among experimental forests we re more closely linked to differences in parent materials. Nine of the 12 soil properties measured differed between control and thinned plot s, and the variance explained by the proportion of basal area removed in the experimental thinnings was always greater than that explained b y 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 appare nt when the chemical properties of soil of the experimental forests we re analyzed individually. We suggest that thinning may have reduced up take, increased relative nutrient availability, changed leaf and litte r quality, and altered decomposition and mineralization rates in such a way as to produce persistent differences in soil properties. (C) 199 7 Elsevier Science B.V.