This contribution evaluates dynamic changes in the content of selected chemical elements (Ca, Mg, K, Na, Fe, Zn, Cu, Pb and Mn) in the aboveground biomass components of 39-year-old red oak (Quercus rubra L.) and black walnut (Juglans nigra L.) stand types from a series of PRAs at Ivanka near Nitra tended by mild crown thinnings. The results revealed that under the effect of thinnings the Ca, K, Na and Zn contents decreased and on the other hand the Pb contents increased.