## 3 Results
### Changes in Norway Spruce Biomass under Different Future Climate Scenarios  
Young, middle-aged, and near-mature forests are the primary types of forests that benefit from thinning as a management strategy [52]. Considering this, in the later stages of the long-term simulation, the spruces in the Hyytiala and Solling sites will reach the mature forest stage. We chose the Bily Kriz site for simulation prediction. We estimated the changing trend of stand biomass and average diameter at breast height using the thinning regimes described and the gathered future climate data in Section 2.4. The ensemble means of three CMIP6 models were utilized to analyze the trend of each meteorological factor (Figure A1). The results indicate that there is a rising trend in the future daily minimum and maximum temperatures, as well as the daily average solar radiation, across all climate scenarios observed at the Bily Kriz site. The results also indicate that, under SSP1-2.6 and SSP2-4.5 scenarios, the precipitation in 2090s increased by 9.79% and 7.02% compared with that in 2010s. On the contrary, under the SSP5-8.5 scenario, the precipitation in 2090s decreased by 12.84% compared with that in 2010s. However, the precipitation in the SSP5-8.5 scenario decreased by 12.84%. The number of frost days had a greater impact on forest productivity. The reduction in the number of frost days persisted because of the steady escalation of the daily minimum temperature within the contexts of the SSP2-4.5 and SSP5-8.5 scenarios. In contrast to the frost days recorded in the 2010s, those observed in the 2090s exhibited a reduction of 40.26% and 69.33% for the respective years. Despite a slight increase in the daily minimum temperature under the SSP1-2.6 scenario, there was no significant alteration in the annual count of frost days. Based on the above climate scenario, we simulated the mean DBH and biomass of Norway spruce at the Bily Kriz site for the 2020-2100 period (Figure 6). Figure 6: The future Norway spruce stand’s mean diameter at breast height and biomass trends at the Bily Kriz site. (**a,b**) show the average diameter at breast height and biomass variation trend of the Norway spruce in 2040, 2060, 2080, and 2100 under several climate scenarios and 18 thinning strategies. Sections (**c,d**) identify the five most effective thinning techniques, based on the average diameter at breast height and biomass estimations of the forest stand in the year 2100. Where (i) represents the value difference between SSP1-2.6 and SSP5-8.5 scenarios, and (ii) Indicates the difference in values between SSP2-4.5 and SSP5-8.5 scenarios. The presented data display the simulated values of stand diameter at breast height and biomass for various thinning techniques in the years 2040, 2060, 2080, and 2100, arranged in a left-to-right formation. The simulation results indicate that the productivity and DBH growth of spruce were most significant in the SSP5-8.5 scenario, regardless of the combination of thinning intensity and interval, when thinning from below was used (Figure 6a,b). Additionally, with the same thinning intensity and a climate scenario with a higher average temperature, the growth of Norway spruce varied more significantly. We selected the five thinning regimes with the highest biomass and DBH values for spruce in 2100 to verify our views (Figure 6c,d). The figures show the difference in spruce's response to the same thinning regimes and different climate scenarios at four time nodes in 2040, 2060, 2080, and 2100. Using the 10Y_H3T thinning approach as an example, the difference in DBH between the SSP5-8.5 and SSP1-2.6 scenarios increased from 0.35 cm in 2040 to 3.01 cm in 2100. The difference in biomass increased from 1.65 h\(\  
structure of the canopy, allowing more light to reach the understory, which promotes forest growth. However, according to the studies described in Section 3.1, the age of the forest is a constraint that causes the photosynthetic efficacy of trees (or AlphaCx) to fluctuate and decline.