## 3 Results
### The Variation of the Soil's Chemical Compositions in Forest Plantations from Waste Heaps

Table 6: Data used for statistical testing models for goodness of fit. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Tested Variable** & **Mean** & **Standard** & **Shapiro–Wilk (S-W) Test** & **Kolmogorov–Smirnov (K-S) Test** \\ \cline{3-6}  & **Deviation** & **S-W Test** & **\(p\)-Value** & **K-S Maximum Values** & **Critical Values** \\ \cline{3-6}  & & **Value** & **Value** & **(\(n\) = 7, alfa = 0.05)** \\ \hline Number of trees & 80.429 & 17.194 & 0.900015 & 0.3756 & 0.18999 & 0.483 \\ \hline Height of trees (m) & 5.057 & 0.976 & 0.7897 & 0.40721 & 0.19307 & 0.483 \\ \hline Diameter of trees (cm) & 4.579 & 0.635 & 0.843857 & 0.126031 & 0.19077 & 0.483 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Shapiro–Wilk and Kolmogorov–Smirnov tests for testing the normality of tree number distribution, their height, and diameters on plots. as the number of trees from the sample surface, the trees' average height, and diameter, the tree volume, the stand consistency (expressed as percentage soil coverage by the crown), the oleaster percentage--this being the main species used in afforestation--and the black locust percentage, cumulated with the percentages of other species. The average difference regarding Fe, Zn, and Cd concentration was calculated for plots where trees' biometric characteristics were measured (V8-V10), compared to analyses in that area before forest vegetation existed on the waste heaps (V1-V7 (Table 8)). The averages of the statistically significant differences in concentration of each analyzed element (Fe, Zn, and Cd) were correlated with the stand's characteristics from sampling points V8 to V14 (Table 9). By calculating the Pearson correlation coefficient between the different characteristics presented in Table 9 and the Fe, Zn, or Cd differences in concentration (2019 and 1988), we obtained both positive and negative correlation coefficients (Table 10). This fact shows the existence of a direct correlation as well as a reversed correlation. They are presented below for each stand characteristic, together with the obtained correlation coefficients. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Pearson Correlation Coefficients Value (\(r\)) for Different Stand Characteristics and Differences on Chemical Element Content**} \\ \hline \multirow{2}{*}{\begin{tabular}{c} **Chemical** \\ **Element** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Number** \\ **of Trees** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Average** \\ **Height of Trees** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Consistency** \\ **Diameter of** \\ **Trees** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Wood Mass** \\ **Volume** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Percentage** \\ **of Oleaster** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Deccentage** \\ **of Oleaster** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Deccentage** \\ **Other Species** \\ \end{tabular} } \\ \hline Fe & 0.5 * & \(-\)0.67 ** & \(-\)0.2 & 0.29 & 0.07 & \(-\)0.34 & 0.34 \\ \hline Zn & 0.56 * & \(-\)0.84 *** & \(-\)0.68 ** & 0.38 & \(-\)0.34 & \(-\)0.29 & 0.29 \\ \hline Cd & \(-\)0.20 & \(-\)0.72 ** & \(-\)0.19 & \(-\)0.31 & \(-\)0.48 * & \(-\)0.42 * & \(-\)0.42 * \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Pearson correlation coefficients value (\(r\)) between Fe, Zn, and Cd differences in concentration (2019 and 1988) and different stand characteristics (*—reasonable correlation, **—high correlation, ***—very high correlation).