In the Forest management unit Mirna Gora, a research site was established in 2019 in mixed pole-stage stands on a submontane beech forest site. Eight research plots were used to compare traditional selective thinning (from above), situational thinning with final crop trees, situational thinning with final crop trees according to Schütz, and control plots without any intervention. With the first remeasurement in 2024, we assessed the effects of different thinning methods on tree growth and evaluated the need for repeating the thinning. In total, we analyzed 192 trees, including all crop trees and a representative number of indifferent trees. We found that the average annual diameter increment of all analyzed trees was 0.42 cm/year. Final crop trees grew best under situational thinning with final crop trees (0.60 cm/year), followed by plots thinned according to the Schütz method (0.53 cm/year), while the lowest increment was observed with traditional selective thinning (0.43 cm/year). The analysis of covariance confirmed statistically significant differences in the average diameter increment of crop trees between thinning methods, but not for indifferent trees. The highest volume increment of crop trees was also observed on plots thinned using the final crop tree method (0.024 m³/year). We found a statistically significant positive correlation between the initial diameter at breast height and diameter increment, as well as between crown size and diameter increment. Five years after thinning, situational thinning with final crop trees proved to be the most effective method for growth encouragement in crop trees, while traditional selective thinning was the least effective. Based on the crown shading and crown size of the crop trees, we concluded that repeated thinning is not yet necessary, and the intensity of thinning carried out was appropriate.
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