Radial distribution patterns of Cd and Zn in stems of Scots pine (Pinus sylvestris L.) trees analyzed 12 years after a contamination event

Radial distribution patterns of Cd and Zn in stems of Scots pine trees (Pius sylvestris L.) were investigated 12 years after a soil pollution event. The trees were growing on experimental plots near Krakow, southern Poland, which had been contaminated with heavy-metal-containing dust in 1980/81. The element distributions were examined for visible signals of the pollution event. Distributions of Cd and Zn in trees on contaminated plots showed elevated concentrations but were not uniform in shape. Only 2 of the 12 examined trees on plots with elevated Cd levels had highest Cd concentrations in xylem rings produced at the time of the pollution event. None of the sampled trees from the Zn plots had highest Zn concentrations in xylem rings which corresponded to the time of the pollution event. In the majority of sampled trees, concentrations of Cd and Zn decreased markedly in rings produced after the application of Cd and Zn dusts. In trees on contaminated plots concentrations of Cd and Zn were generally higher in sapwood than in heartwood. A sharp decline of both elements across the sapwood-heartwood boundary was observed. The distribution patterns of Cd and Zn are discussed with respect to endogenous physiological processes in stem wood. The element patterns observed in the wood of individual trees did not correspond to the known timing of pollution inputs to respective forest stands.