Radial variations in wood mineral element concentrations: a comparison of beech and pedunculate oak from the Belgian Ardennes

Radial variations in wood mineral element concentrations (N, P, Ca, Mg, K, Mn, Al) were investigated in 5 oak trees (a ring-porous species with typica l heartwood) and 5 beech trees (a diffuse-porous to semi-ring porous wood s pecies lacking typical heartwood) growing on an ochreous brown earth in the Belgian Ardennes. Differences in concentration profiles were consistent wi th the difference in wood structure. Specifically, oak had markedly higher concentrations in sapwood, suggesting that nutrients are actively resorbed from senescing wood rings, resulting in very low elemental concentrations i n heartwood. Similarities between the two species, including outwardly decr easing cation concentrations and a recent increase in Al concentration, mig ht be ascribed to a common environmental influence, i.e. soil leaching by a cid rain. However, the decrease in Mn concentration in both species is not consistent with a scenario of decreasing soil pH. Alternative explanations are discussed.