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ŠUMARSKI LIST 5-6/2015 str. 46     <-- 46 -->        PDF

minimize the damage. This resulted in a large number of damaged plants. In addition, young spruce plants are less strongly rooted in comparison to young beech trees, which caused a more severe uprooting of the regeneration.
During the timber extraction positioned parallel to contour lines, the assortments usually turn around their axis, which commonly causes injuries to residual trees and the regeneration. The worst case is when the assortments are positioned parallel to skid trail or at an acute angle to the trail to which they are being skid (Figure 5).
If the regeneration height is small, in most cases, there is no severe damage, whereas the situation differs if the plants are tall and large in diameter. If extraction is carried out perpendicular to contour lines, front ends of logs cause damage to plants in the form of bark peeling and uprooting.
After formation of the optimal load, logs were transported to a roadside landing by skid trail. During timber skidding, the front ends of attached assortments were lifted off the ground, while the rear ends of the load had a certain degree of freedom of movement taking the shape of a fan. Therefore, the load became wider than the tractor, which resulted in damage to the stems and the regeneration along the skid trail.
During timber skidding, the most common type of damage to standing trees is damage to the butt end, and much less to the root collar or stems (Figure 2). Injuries to the butt end (bark peeling and superficial wounds) occurred by 8.22 % more frequently in the pure stand than in the mixed stand. The numbers of wounds to the root collar and the stem are higher in the mixed stand than in the pure stand by 35.38 % and 13.78 %, respectively. Uprooting was mainly found in thinner trees with diameters at breast height ranging from 9 cm to 12 cm. On the basis of a research of damage to trees in the timber extraction in beech forests, Behjou (2014) pointed out that out of the total of 489 trees located along the skid trail, 339 trees (69 %) suffered some type of damage.
Damage to the regeneration occurring during the timber skidding does not differ significantly from the damage to the regeneration incurred during winching. In this case, the number of wounds per winching operation was 2.52 times higher in the mixed stand than in the pure stand.
The average area of wounds in the form of bark peeling on the root collar and the butt end during the timber extraction is by 21.46% greater in the pure stand compared to the average area of wounds in the mixed stand. The areas of most wounds range from 50 to 200 cm2, which represents 57.6 % of all injuries in the mixed stand and 60.6 % in the pure stand. The research results of other authors who have investigated this issue on different tree species and in different conditions indicate that wound areas are most commonly greater than 200 cm2 (Solgi and Najafi 2007; Ficklin et al. 1997; Tsorias and Liamas 2010). In the research Froese and Han (2006), 84 % of wound areas were smaller than 194 cm2. If minor wounds are concerned, damaged trees can continue with their growth and they should not be cut down but left to serve as protection to other trees in case of a repeated timber extraction (Doležal 1984).
The following conclusions can be reached on the basis of the results of this survey:
- The number of damages in a stand increases significantly with an increase in the diameter at breast height of felled trees.
- The largest share of damage to residual trees during felling in both the mixed and pure stands is to the crowns