Soil and Tree Ring Chemistry Changes in an Oak Forest

Changes in soil chemistry due to historic large-scale disturbances, e.g. pollution inputs, storm damage, and logging, have previously been shown to cause similar changes in the nutrient concentrations found in tree rings. Repeated soil sampling in a reference watershed at the Coweeta Hydrologic Laboratory (Otto, NC) in 1970, 1990, and 2004 showed significant decreases in cation concentrations and soil pH. It was hypothesized that historic wood nutrient concentrations could be used as a surrogate to estimate earlier soil cation concentrations. We hoped to exploit a relationship between recent soil and wood chemistry measurements to predict older soil chemistry values based on dendrochemical analysis. Oak trees (Quercus alba and Q. prinus) located in the reference watershed adjacent to long-term soil sampling plots were cored and analyzed for cation concentrations in 5-year increments. No significant relationship was found between the soil and wood chemical compositions for any given time. This indicates either that cation availability in the soil has not yet become a limiting factor for tree growth at this site, or that trees can access a source of nutrient cations other than the soil exchangeable cation pool.