DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 5-6/2015 str. 45 <-- 45 --> PDF |
in the pure and mixed stands. However, differences in the frequencies of occurrence of different types of damage within the same phase are not significantly different. The differences that do exist can be explained by the impact of shape and size of the crown on the one hand and the number of trees per unit area on the other. The number of wounds to residual trees was 1.41 per felled tree in the mixed stand and 1.84 in the pure stand. Therefore, it can be calculated that the number of wounds per tree in the felling phase is by 30.50% higher in the pure stand than in the mixed stand. The explanation for the larger number of injuries in the pure stand may be the fact that the crowns of beech trees are more developed (usually containing forked branches) than the crowns of spruce and fir trees, which leads to deviations from the desired felling direction and major damage to neighboring trees. In both sample plots, it was found that in the felling phase the most common type of damage is to the crown, which is followed by damage to the stem, damage to the butt end and damage to the root collar (Graph 1). Behjou and Mollabashi (2012) reported 1.35 wounds to the crowns of neighbouring trees per felled tree during felling in an unevenaged beech stand. In a spruce stand in Norway 55% of the trees damaged during felling with chainsaw suffered damage to the crown (Fjeld and Granhus 1998). According to a research performed in Finland (Siren et al. 2015) in uneven-aged spruce stands, almost 70% of the damage incurred during selection cuts with a harvester was to the stem in the form of bark peeling, damage to wood and stem breakage. Damage to the root collar is the least common due to the fact that during felling the place where the trees fall is usually outside the range of the root collar. Nevertheless, the average number of injuries to the root collar of neighboring trees was significantly higher in the pure stand than in the mixed stand, primarily due to the wider crowns. In addition, it was found that the number of wounds increased with an increase in the diameter of felled trees. This is due to the fact that thicker trees are also higher and have longer and wider crowns, as well as greater wood volume, which makes them more likely to cause damage (Table 4). A large number of wounds to the regeneration were recorded in the mixed stand during the felling phase. The number of injuries to the regeneration per felled tree was 2.98 times higher in the mixed stand than in the pure stand, as a consequence of higher density of regeneration in the mixed stand. This damage can occur in the form of tree topping, breakage, breaking off of the branches, bark peeling and uprooting of the regeneration. The regeneration in the form of seedlings (young plants) is fairly resistant to bending due to their small height and thin stems. Therefore, after the branches and trunks that fell on them are removed, they can continue with their growth. In the phase of tree felling, the average wound area is by 62.50% larger in the mixed stand (390 cm2) than in the pure stand (240 cm2). Similar results were obtained by Nikooy et al. (2010) who investigated the damage in mixed broadleaf stands, where the average wound size per tree reached 290.31 cm2. According to a research (Siren et al. 2013) of selection cuts with a harvester in a spruce stand, the average wound area per tree was 71.7 cm2. During the phase of timber extraction, damage was recorded to both residual trees and the regeneration. During the timber winching, the most common type of damage was to the root collar of residual trees in the stand. In addition, partial or complete uprooting of trees was observed, while there was no damage to the butt end. The number of injuries to the root collar was by 17.61% higher in the mixed stand than in the pure stand. On the other hand, the number of injuries to the stem was by 42.29% higher in the pure stand than in the mixed stand. In the survey of damage to residual trees in a selection stand of beech, fir and spruce Sabo (2003) reported an 84% share of damage to the root collar in the total number of injuries. During timber extraction, damage to the regeneration is inevitable. The recorded number of injuries to the regeneration was 2.44 times higher during the timber winching in the mixed stand than in the pure stand. In this case, the explanation may be sought in the number of trees per unit area in the mixed stand. Due to a large number of trees per hectare, in some cases it was necessary to deviate from the skidding direction determined during felling, in order to |