3.2.2. Bark
The highest Cu and Ni concentrations of all the sampled compartments were those of pine bark from the control plots (Figure 2). The t-test showed that the between- treatment difference was statistically significant for the Cu concentrations
(t = 4.039; p = 0.016). The mean Cu concentration of the birch bark was slightly higher on the mulch plots, but the difference was not statistically significant. The corresponding Ni concentrations were about the same for both treatments (Figure2).