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ŠUMARSKI LIST 5-6/2015 str. 40     <-- 40 -->        PDF

trees in a stand, regeneration density, felling intensity, diameters of trees, sizes of crowns, felling direction, slope of the terrain, the method of wood assortment processing and the operator’s skills. However, it also depends on the density of the primary and secondary road networks. The occurrence of damage to trees has a particular significance in even-aged and uneven-aged stands, where only a part of the standing volume is removed by felling (Ostrofsky 1988). Damage to trees and the regeneration occurring at the stage of felling and transport of timber represents one of the most stressful events in forest management (Dvorak and Iordache 2010). Tree wounds are often suitable areas for the emergence of various diseases that can cause physiological decline of trees (Vasiliauskas 2001), and quality of the residual trees is an important factor of the future stand value (Bobik 2008).
Elements of the proposed systems of felling should be harmonized with respect to the characteristics of the forest, type of machinery and felling intensity, in order to include variable factors that affect the efficiency of work (Akay et al. 2004). As a result of damage caused to trees, soil and ground vegetation, timber extraction is considered the most delicate stage of operation in forestry, especially in protected areas.
In order to reduce damage to residual trees and the regeneration during the operations of felling, processing and transport of wood assortments, it is necessary to pay attention to directional tree felling and choice of an adequate skidding facility (Campbell 2003), as well as proper distribution and density of forest road infrastructure.
The choice of technique and technology of work has marked impact on the degree of damage to residual trees, the regeneration and assortments (Eroglu et al. 2009). Some authors have pointed out that the timber extraction with skidders in areas with steep slopes (50 – 70%) leads to significant damage, and that the best solution on such a terrain is a cable yarder. Spinelli et al. (2010) found 12-14% of damaged trees in a stand when conventional felling and timber extraction with adapted agricultural tractors were applied.
A number of researchers (Limbeck-Lilienau 2003; Poršinsky and Ožura 2006; Solgi and Najafi 2007; Tsorias and Liamas 2010, etc.) have investigated damage to residual trees in the stand after the technological processes of felling and transport. Most of these researchers used classification of the type of damage after Meng (1978).
According to the research of Solgi and Najafi (2007) in the forests of beech and hornbeam in Iran, during the timber extraction with a skidder, the most common type of damage is to the root of residual trees, accounting for as much as 41% of the total damage. The authors point out that during timber extraction in mixed stands, thick and forked branches should be removed, because in this way, damage to residual trees is significantly reduced. According to the research Danilović et al. (2011) the notching and bending of thick branches can significantly decrease damage to residual trees in a stand.
Tsorias and Liamas (2010) observed that during the transport of wood assortments in mixed forests of beech and oak by skid trail with an adapted agricultural tractor, most injuries occur to the stem in the area of up to 2 meters on