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ŠUMARSKI LIST 3-4/2017 str. 61     <-- 61 -->        PDF

slope map of the study area (Table 3, Figure 4). When the roads are constructed in mountainous terrain, the excavated materials from the hillside are widely scattered downward the slope (Kim et al. 2004; Hosseini et al., 2012). Properly locating a road depends on the type of road, geology, land use, hydrological network and the side slope of the ground. Evaluating the needs of forest roads of an area is fundamental to evaluate together with the accessibility of the forest and also the possibility to perform the silvicultural operations (Pellegrini, 2012). The clearing limit of roads and skid trails will vary, depending on ground slope and the amount of cut and fill required (Kramer, 2001). Ground slope is the most significant parameter influencing the off-road transportation (timber extraction) and consequently the choice of the extraction system. Therefore, we considered technical limits as per table 2, to select the appropriate extraction systems generally limited by distance from the road.
Aspect associated parameters such as exposure to sunlight; drying winds and rainfall are important factors in forest road and timber extraction systems. A road along the slope which gets the most sun will dry out faster after rainfall. Consequently, it will be subject to less damage from traffic thereby resulting in lower maintenance cost (Sessions 2007; Hosseini et al., 2012). Therefore, we prepared an aspect map and displayed that all aspects were presented in the study area (Figure 5). The largest areas of aspect are northwest, west and southwest directions, while the smallest areas are flat (Table 4).
Existing forest roads were digitized and a database was built using GIS as shown in Figure 6.
One major challenge in secondary road network planning is to determine timber extraction systems under different terrain conditions. Ground slope and topography which affect the forest road network were considered as correction