## 3 Results
### Average Daily Sap Leakage by Phase  
A considerable variation in the amount of birch sap leakage was observed in the individual harvesting stages. The smallest amount of sap was found in the initial stage, for which an average of 2.6 dm\({}^{3}\) was obtained from one tree in the mixed coniferous forest and broadleaved forest sites, and an average of 3.2 dm\({}^{3}\) was obtained in the mixed coniferous forest site (Table 4). A slightly higher sap yield was noted in the final phase, for which the average values ranged from 3.4 dm\({}^{3}\) in the broadleaved forest site to 5.8 dm\({}^{3}\) in the mixed coniferous forest site. On average, the largest amount of sap was obtained in the main phase, from 5.3 dm\({}^{3}\) in the broadleaved forest site to 8.0 dm\({}^{3}\) per day in trees representing the mixed coniferous forest site. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Phase** & \begin{tabular}{c} **Number** \\ **of Trees** \\ \end{tabular} & **Mean** & **Minimum** & **Maximum** & \
\begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} &
\begin{tabular}{c} **Coefficient** \\ **of Variation** \\ \end{tabular} \\ \hline \multicolumn{6}{c}{Site: mixed coniferous forest} \\ \hline Initial & 9 & 2.6 & 0.8 & 4.4 & 1.2 & 45.7 \\ Main & 9 & 8.0 & 4.2 & 14.9 & 4.2 & 53.3 \\ Final & 9 & 5.8 & 0.6 & 13.4 & 5.1 & 88.4 \\ \hline \multicolumn{6}{c}{Site: mixed broadleaved forest} \\ \hline Initial & 9 & 3.2 & 0.3 & 8.5 & 2.3 & 70.4 \\ Main & 9 & 6.3 & 1.3 & 14.8 & 3.8 & 60.6 \\ Final & 9 & 3.9 & 0.1 & 15.4 & 4.6 & 118.2 \\ \hline \multicolumn{6}{c}{Site: broadleaved forest} \\ \hline Initial & 9 & 2.6 & 0.4 & 5.7 & 1.9 & 73.7 \\ Main & 9 & 5.3 & 1.9 & 12.0 & 3.4 & 63.7 \\ Final & 9 & 3.4 & 0.4 & 9.3 & 3.0 & 88.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary statistics for daily sap leakage by phase (dm\({}^{3}\)/tree). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Tree** & \multicolumn{4}{c}{**Site**} \\ \cline{2-5}
**Parameter** & **Mixed Coniferous** & **Mixed Broadleaved** & **Broadleaved Forest** & **Total** \\  & **Forest** & **Forest** & **Broadleaved Forest** & **Total** \\ \hline Diameter at breast height & \(-0.32\) & 0.32 & \(-0.05\) & \(-0.05\) \\ Total height & 0.38 & 0.44 & \(-0.50\) & \(-0.13\) \\ Crown base & 0.49 & 0.44 & \(-0.21\) & \(0.05\) \\ Crown length & \(-0.12\) & 0.10 & \(-0.31\) & \(-0.21\) \\ Relative crown length & \(-0.32\) & \(-0.15\) & \(-0.17\) & \(-0.18\) \\ Slenderness & 0.55 & \(-0.17\) & \(-0.13\) & \(-0.01\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: [PERSON]’s rank correlation coefficient between biometric features of trees and birch sap yield. For individual trees, the extreme values of the average daily birch sap yield ranged from 0.1 dm\({}^{3}\) to 15.4 dm\({}^{3}\) (the final phase for tree THN1 in the mixed broadleaved forest site; Table 4). The trees showed large variations in the amount of birch sap harvested, even within the same site and phase. The smallest variation was observed in the initial phase, for which the coefficient of variation ranged from 45.7% in the mixed coniferous forest site to 73.7% in the broadleaved forest site. In the main phase, the values of this measure were the closest to each other in the individual habitats. They amounted to 53.3% in the mixed coniferous forest site, 60.6% in the mixed broadleaved forest site, and 63.7% in the broadleaved forest site. The most significant variation in the amount of sap harvested between trees in the site was observed in the final phase, for which the coefficient of variation in the mixed coniferous forest and broadleaved forest sites was around 88%, and the highest value was in the mixed broadleaved forest site (118.2%). Using a two-factor analysis of variance, we examined whether the forest site type or the sap collection phase affects the variation in the average amount of harvested sap. Statistically significant differences were found in the average amount of harvested sap depending on the collecting phase (F = 7.987, \(p\) < 0.0007).