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ŠUMARSKI LIST 1-2/2015 str. 38     <-- 38 -->        PDF

Skidder extraction is the most commonly used method for timber extraction in Romania. This is mainly due to the poorly developed forest road network, which hinders the efficient utilization of cable yarders and forwarders. Enhancement of forest infrastructure is prerequisite for the entire wood value added chain and should consider a priori a thorough qualitative and quantitative assessment of the existing road networks. But planning new roads should also consider the most suitable harvesting systems for local conditions (Kühmaier and Stampfer 2010). An important phase in this process is the calculation of the real mean extraction distance (Pentek et al. 2005). Since one of the most important parameters for the optimization of forest road networks is the minimization of the total costs of timber extraction (Ghaffariyan et al. 2010), the mean extraction distance can be used for determining the necessary length of new forest roads and their possible layout. For this purpose, an accurate determination of the extraction distance is required. Several studies highlight the necessity of using correction factors for adapting theoretical models to real life situations. Mathews (1942) first established the theoretical framework of forest openness. Segebaden (1964) addressed the relationship between the mean extraction distance and the road network density, introducing two factors for adjusting the ideal geometric model to the specific local conditions: the road network correction factor (V-corr or kn) and the extraction correction factor (T-corr or ks). Addressing several theoretical models of road networks, Lünzmann (1968) defined the coefficient of opening-up (kt) also known as the total correction factor, highlighting the factors which influence its determination. Amzica (1967; 1971) stressed the necessity of accurate determination of ks and kn.
The importance of one sided versus two sided opening of forest areas and the buffer zone concept for computing the coefficient of openness were introduced by Backmund (1966). Lünzmann (1968) demonstrated the applicability of these concepts based on a cost minimization approach. Hentschel (1999) and Janowsky (2001) showed GIS approaches for comparing different methods for calculating structure indices of road networks, focusing on the optimization of road networks with multiple uses. Lotfalian et al. (2011) described a basic method for determining the correction factor used in the computation of the real mean extraction distance. Contreras and Chung (2011) showed a model for generating optimal skid-trail networks. Krč and Beguš (2013) elaborated a GIS based model for determining the necessary density of forest roads, while Enache et al. (2013) presented a multiple criteria decision support tool for bench marking forest road scenarios.
The aim of this study was to show how computation of the mean extraction distance and of the correction factors can be done more efficient and effective using process automation in GIS and how extraction distance can be used in the evaluation of forest road options.
Materials and methods
Materijali i metode
Study area – Područje istraživanja
This study was conducted in a 903 ha private forest located in the South-Central Carpathians of Romania, in Brasov county. The most common forest types in this area are: mountain beech forests on shallow soils with mull flora and mixed fir-beech forests with mull flora of medium productivity. The geology is marly-flysch, sandstones and massive conglomerates. The hydrological network has permanent water streams with peak flows in spring. One fifth of the study area is located on gentle slopes (<20%) and about 10% is steep terrain (slopes >55%). The annual allowable cut is about 4310 m3and timber harvesting is performed by local contractors with skidders and tractors. Forest traffic infrastructure consists of 11.7 km of forest roads and 71.5 km of skid trails. The skid trails were mapped in GIS on foot, using a GPS Garmin 60 CSx GPSMAP at recording intervals of five seconds.
Computation of mean extraction distance and other structure indices – Izračun srednje udaljenosti privlačenja drva i ostalih pokazatelja učinkovitosti mreže primarnih šumskih prometnica
The most important structure indices of the forest traffic infrastructure are: road density or road network density index (RDI), road distance (RD), mean extraction distance (SD) and relative openness (OR). Road density is the ratio between the length of the forest road network and the area of the served forest (Bereziuc 1981), while road distance is expressed in meters as the ratio between surface of 1 ha (in m2) and the road density (Dietz et al. 1984). Segebaden’s (1964) definitions of geometric extraction distance (i.e. the shortest straight line distance from a given point to the nearest road) and of the mean extraction distance (i.e. arithmetical mean of the geometric extraction distances) were used in this study. Relative openness is determined by dividing the opened forest area for the real mean extraction distance to the total forest area analysed (Pentek et al. 2005). For computing these indices, classical analytical methods and GIS methods were used. For testing if there were significant differences between methods, the results were statistically analysed in PASW® Statistics 18 SPSS.