In the area of Trnovski gozd, we analyzed the vitality of European beech and its effect on tree diameter growth within the forest management unit Predmeja. We inventoried and analyzed five groups of five permanent sample plots along a transect that captured a cross-section of the Trnovski gozd plateau from its southern edge toward the interior. For all beech trees on the selected permanent sample plots, we visually assessed tree crown defoliation, vitality, and crown damage, focusing on external factors such as insect activity and frost damage. Diameter increment was calculated using data from the last three inventories conducted by the Slovenia Forest Service. The observed low average crown defoliation indicated good beech vitality in the area. Vitality did not improve gradually from the plateau edge toward its interior: the lowest vitality was observed at both the plateau's outer edge and higher altitudes, while the best tree vitality was recorded in the middle of the transect. The average diameter increment of beech trees decreased from the period 2003-2012 to 2013-2022. Contrary to expectations, tree vitality did not significantly affect diameter growth. Differences in average diameter increment among vitality and crown damage categories were not statistically significant. No clear relationship was found between diameter increment and crown defoliation, even when accounting for diameter at breast height. Insect activity and frost caused increased defoliation but did not affect diameter growth.
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