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ŠUMARSKI LIST 3-4/2017 str. 59     <-- 59 -->        PDF

mobile tower yarder. Loading operations at the roadside or landing is carried out manually with grapple loaders or hydraulic cranes. Hauling through forest roads and main roads is executed by truck and tractor trailer from roadside to the main storage site.
Methods – Metode
Geographic data used in this study were acquired from on-screen digitized paper maps in an ArcGIS environment. These maps consist of topographical maps containing elevation data (10 m contour interval), forest management plan information, forest road network, administrative boundaries, hydrology network and technical limitations for timber extraction systems. Topographic vector maps of 1:25000 scale were used in this study. These maps were produced by the General Command of Mapping of Turkey using Universal Transvers Mercator (UTM) projection and ED-50 datum. Therefore, the original projected coordinate system, UTM, European Datum 1950, Zone 37N, was selected for all maps.
An inventory of forest roads not existing in the digitized maps was conducted using GPS (Global Positioning System). Road routes were also collected with track mode of GPS. GPS data were converted into a GIS format using Pathfinder Office software. Field descriptions of continuous segments and discrete features were added to GPS location information to create a series of GIS coverages. A separate data layer (coverage) was made of each road feature mapped. The created layer was then used to calculate forest road density, road spacing and road coverage. Road density was obtained using the formula (1), road spacing was determined theoretically using the formula (2) and road coverage was calculated according to formula (3) as follows Backmund (1968):
                RD=road length (m)/district area (ha)               (1)
                RS=10000/RD        (2)
in which RD was Road Density and RS was Road Spacing.
                Road coverage:                    (Accessible areas for logging) / total areas*100            (3)
Timber extraction systems were determined on the basis of the following: ground slope, extraction direction, extraction distance, forest road network, elevation and boundaries. The Digital Elevation Model (DEM) of the study area was created with ArcGIS 10.0 software. Ground slope, aspect, and elevation maps were derived from the DEM.
Ground slope is one of the most important parameters determining the choice of an extraction system. Ground slope was calculated using the slope tool of the Spatial Analyst toolbox. Five main slope classes (in percentage) were defined according to Samset (1979) (Table 1).
Aspect associated parameters such as exposure to sunlight; drying winds and rainfall are important factors in forest roads. Slope direction map of the study area was divided into 9 directions including flat, north, northeast, east, south, southeast, southwest, west and northwest.
The mean extraction distance (off-road transportation defined as the average distance between stem-site and the next forest road or storage place for further transportation, was grouped into five classes as follows: Class 1, <100 m; Class 2, 100–250 m; Class 3, 250–500 m; Class 4, 500–1000 m; Class 5, >1000 m. The extraction distance was generated via „Euclidean Distance Tool” using the roads shapefile (Tucek and Pacola 1999; Lubello, 2008). Although the maximum distance may be changed according to user, it was set up to 1000 m. as default.
Five main harvesting systems were selected for harvesting operations in the researched area considering timber extraction systems and felling method (Figure 1). Some factors such as working direction, ground slope limits, operation distance were found to be different according to the selected system. Therefore, to determine the timber extraction systems, studies previously conducted were used (Aykut et al. 1997; Acar 1997; Acar 1998; Çağlar 2002; Öztürk and ªentürk 2006; ªentürk et al. 2007) (Table 2).