Seasonal variations in concentrations and radial distribution patterns of Cd, Pb and Zn in stem wood of beech trees (Fagus sylvatica L.)

Radial distribution patterns of Cd, Pb and Zn in stem wood of beech trees (Fagus sylvatica L.) in Germany were determined before, during and after the growing season. Element concentrations differed significantly between the sampling dates. Concentrations of Cd and Pb were higher in December and April than during the growing season in June and September. Highest levels of Zn were found in April and lowest in September or December. Shifts in mineral composition of stem wood are discussed in relation to physiological processes during the annual cycle of growth. Radial distributions of Cd showed increasing concentrations from the cambium towards the pith. Pb levels had a peak near the sapwood-heartwood boundary. Highest Zn levels were found near the cambium and the pith. The shapes and levels of these patterns were not stable during the annual growth cycle, i.e. they are not reliable sources of information about former pollution levels.