## 4 Discussion  
### NPP Biometric Estimates  
Forests absorb carbon dioxide in the process of photosynthesis. Part of it is fixed in plant biomass (carbon sequestration), while some returns back to the atmosphere through ecosystem respiration. In this study, biometric measurements and derived site-specific allometric equations (M1/M2 method) showed that, on average, 2.0/2.1 t C ha\({}^{-1}\) was sequestered in wood tissues of a 25-year-old Scot's pine stand (annual NPP totals) in dry 2019. In the following year, characterized by moderate water availability, these values \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multicolumn{2}{c}{**2019**} & \multicolumn{2}{c}{**2020**} \\  & **M1** & **M2** & **M1** & **M2** \\ \hline Total stem increment of an average tree & 0.142 \(\pm\) 0.01 & - & 0.164 \(\pm\) 0.01 & - \\ (cm)—denrometers & & & & \\ \hline Total increase in dry biomass of an average tree (kg) & 0.942 \(\pm\) 0.070 & 0.978 \(\pm\) 0.072 & 1.206 \(\pm\) 0.070 & 1.255 \(\pm\) 0.073 \\ \hline Total biomass of the stand at the end of growing & & & & \\ seasons (t ha\({}^{-1}\)) & 203.387 \(\pm\) 0.295 & 204.017 \(\pm\) 0.306 & 208.861 \(\pm\) 0.298 & 209.714 \(\pm\) 0.310 \\ \hline Total increase in dry biomass of the stand (t ha\({}^{-1}\)) & 4.273 \(\pm\) 0.295 & 4.439 \(\pm\) 0.306 & 5.473 \(\pm\) 0.298 & 5.697 \(\pm\) 0.310 \\ \hline Total NPP (t C ha\({}^{-1}\)) & 2.137 \(\pm\) 0.148 & 2.220 \(\pm\) 0.153 & 2.737 \(\pm\) 0.149 & 2.849 \(\pm\) 0.155 \\ \hline GPP total during vegetation period (t C ha\({}^{-1}\)) & & 14.70 & & 14.49 & \\ \hline NEP total during vegetation period (t C ha\({}^{-1}\)) & & 5.00 & & 4.50 & \\ \hline CUE for vegetation period & 0.15 & 0.15 & 0.19 & 0.20 \\ \hline GPP total during B (t C ha\({}^{-1}\)) & & 11.79 & & 11.74 & \\ \hline NEP total during B (t C ha\({}^{-1}\)) & & 3.70 & & 3.19 & \\ \hline CUE for B & 0.18 & 0.19 & 0.23 & 0.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the dry biomass estimations including above- and belowground biomass for two site-specific allometric equations M1 (one equation for the whole tree) and M2 (separate formulas for tree components), based on dendrometers and in situ biometric measurements, including deadwood and understory (NPP) as well as NEP and GPP values derived from the eddy covariance observations. B—wood growth period. were 2.6/2.7 t C ha\({}^{-1}\) (Table 3). Among various forest types, boreal forests are the least productive (the lowest annual NPP totals) in comparison to temperate and especially tropical forests. The results from the global studies conducted by [PERSON] et al. suggest that, on average, less than 10 tons of carbon per hectare is assimilated in boreal forests in the form of new woody tissue, while more than 12 tons of carbon per hectare is sequestered in temperate forest ecosystems [48]. On the other hand, [PERSON] et al. [48] have shown that across biomes, the highest NPP is found in middle-aged forests (mean = 6.5 t C ha\({}^{-1}\)), while young forests showed the lowest NPP (average = approx. 4 t C ha\({}^{-1}\)) [48]. The respective results presented in our study indicate annual NPP totals several times lower than the average for boreal forests, and roughly two times lower than the average for young forests, even though the research was conducted at a Scots pine stand located in a temperate climatic zone. This surprising outcome is likely related to the young age of the stand, and further to the extreme meteorological conditions that occurred in the year 2019 (extreme drought) and slow recovery in 2020, in which the impact of the previous year's conditions was still noticeable. Another reason for these lower values could be the differences in methodology between cited study presented above, which covers various species of the climatic zones, while our study concerns only one dominant tree species. [PERSON] et al.