## 4 Discussion
### NPP Biometric Estimates
This research considered different climatic conditions of a 30-year norm, where the year 2005 was identified as hot and dry, 2006 as hot and wet, 2007 as warm and dry, and 2008 as a nearly average year. In another study conducted in a managed forest (afforestation) with predominantly _Pinus halepensis_ species (Yatir Forest, Israel), annual CUE ranged from 0.38 to 0.42, depending on the method used [51]. Thus, it can be conluced that in relation to similar ecosystem types (temperate pine forest), the CUE values presented in our study are quite low. It is worth emphasizing that wood growth is even more drought sensitive than photosynthesis itself [24; 55; 56]. Nevertheless, when severe drought occurs, the photosynthesis rate slows due to stomata enclosure, and biomass growth is also reduced [57]. In the research by [PERSON] et al. conducted at a temperate beech forest, it was shown that annual GPP totals were significantly lower in years when drought occurred, compared to wetter years; a corresponding significant decrease in NPP was also seen [24]. Hence, in dry years the annual NPP/GPP ratio was still quite high (40-44%). The data shows that the reduction in annual net primary productivity in our study is related to the occurrence of conditions distant from the comfort zone (in this case, the occurrence of drought). This can be explained by the adaptation process in which forest ecosystems adjust their optimal productivity to the climatic conditions of the region that used to be close to the average [2]. In addition, [PERSON] et al. [2] observed a negative relationship between NPP and air temperature, which is opposite to the common understanding of the NPP climate response in forests [58]. Such effect also seems true for our research, where a lower NPP total occurred in the warmer year. However, this was more likely caused by drought and/or heat stress, which are generally limiting conditions of NPP in warmer years [59]. Importantly, our results are based on only two years of data (one of which being extreme climate conditions), making them less reliable in supporting the findings of [PERSON] et al. [2]. Moreover, summer of 2020 was cooler, such that the total GPP sum was lower than in the previous year. A higher total NPP is recorder in years characterized by dry conditions--for example in the research by [PERSON] et al., who found a relatively high NPP during the extremely dry 2003, which is even more difficult to explain [24]. One possibility is interannual growth buffers such as C reserves and buds preformed in the previous year, especially if it was climatically medium or wet. This was not the case in our study, since 2019 followed a very dry year, which probably also influenced the presented biomass growth results. The average value of the SPEI index from March to October in 2018 amounted to \(-\)1.64. Extreme drought was evident in June (SPEI = \(-\)2.36) and August (SPEI = \(-\)2.09). Furthermore, extreme conditions such as drought often hinder thorough analysis and interpretation, as well as different physiological responses of plants to the existing conditions. Plants adopt a special \"strategy\" as they partition resources among different organs for optimal functioning. This helps to maximize life span, seed production, and growth rate under particular environmental conditions [60]. It was found that in a tropical forest, the lowest CUE (0.35) occurred in undisturbed forest patches, while slight forest disturbance had a positive effect on CUE increase (0.62) [7]. Moreover, the authors of this study suggest that monocultures had a higher CUE than mixed forest stands. In our research, the difference in NPP resulted in approximately 0.600 t C ha\({}^{-1}\). Applying the literature-derived method (excluding dead branches) yielded in 0.566 t C ha\({}^{-1}\) for the ME site [1]. The literature-derived absolute sums of biomass and NPP were approximately 20-30% lower than those calculated by constructing equations based on in situ data, which amounted to 1.7 C ha\({}^{-1}\) for 2019 and 1.9 C ha\({}^{-1}\) for 2020.