Reconocimiento superior pero igual posición simple

The purpose of forest roads planning is sustainable forest management with minimal risks for environment. The first task of this job is to find optimal spatial layout of forest roads network considering economic and environment aspect.

Piĉman (1994) based the optimal forest road density on economic factors, considering also topographic and hydrological factors which he separated by DTM. His research was placed in NP Medvednica, so he also considered recreational and touristic significance of the area.

The position of forest roads can be determined by comprehensive analysis of the economical-technical criteria, but in the second phase of planning, the ecological and sociological terms of the certain area have to be considered too while fulfilling minimal technical characteristics of the route (Pentek, 2002, Pentek et al., 2005).

Determination of forest road density depends on affecting factors: harvesting methods, different type of roads, the ratio of each road to the whole network, growing stock, slope, geological conditions, presence of material for constructing surface of roads, capital interest rate, timber extraction cost, type of extraction vehicle, slope and length correction coefficient, routes, logs of assortments, allowable winching distance, brush and underbrush, condition of the roots, silvicultural methods, type of soil, altitude, direction of the slope and morphology of forest and terrain. Optimal density of forest roads for stand volume of 353 m³/ha and different type of determination of skidding cost (contract and accounting method) is 19 to 23 m/ha for this forest area (Lotfalian et al., 2008).

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Factors of environment which are taken into account when planning forest roads are divided into six groups: soil, water, biosphere, atmosphere, socio-economic and cultural resources. Construction of forest roads causes the loss of productive and habitat area, damages of water sources, and the atmosphere effects on quality of forest roads (Gumus et al., 2008).

During the optimization of the forest road network (Sokolović et al., 2009), the following factors have to be considered: normal timber growing stock, terrain slope and depth of soil.

According to these factors, thematic maps are made based on the maximal and minimal values which are reclassified and graded, and their overlapping, that is, raster summing, shows the areas suitable for forest road construction.

Abdi et al. (2009) developed a method by using GIS and Multi Criteria Evaluation (MCE) to design a forest road network with the minimal construction cost. They identified six factors which were standardized to a range of 1 to 5. The results of Analytic Hierarchy Process (AHP) have showed that weight of slope is 0.44, weight of soil is 0.24, weight of geology is 0.161, weight of aspects is 0.08, weight of altitude is 0.044 and weight of growing stock is 0.025.

Analysis of different forest road layers construction, based on experts’ experience by the usage of AHP, showed slope with coefficients 0.216, hydro with 0.211, geology with 0.195, soil with 0.151, volume with 0.101, type of forest with 0.049, aspect with 0.047 and elevation with 0.030. Eight studied layers can be divided into two major classes, the most important layers (value more than 0.125) and the least important layers (value less than 0.125). Potential map for forest road planning was created by overlaying all layers with different coefficients. The study area from forest road construction point of view was classified into five classes: very good, good, average, bad, and worse (Mohammadi et al., 2010).

During preparation of the Master plan of forest accessibility in RS, Potoĉnik et al. (2011) used terrain slope, soil depth, normal and existing growing stock in the multi-criteria analysis, whose values were graded and transformed into rasters whose sum gave the areas suitable for forest road construction.

Enache et al. (2011), during the planning of the forest roads, considered geomorphologic relief elements of the observed area. There were 17 km of roads placed with the density around 43 m/ ha and distance between them was 234 m. It was estimated that the construction cost was around 36.8 €/ m. The planned forest roads shortened the skidding distance, and of course, cost was reduced for about 5.3 €/ m^3, which was the research goal.

Decision making group classified important criteria with ponders for forest road located in Haraz region, Mazandaran, Iran: technical features (0.271), transportation (0.084), features (0.434), usage (0.138), road construction with minimal excavation (0.027) and destruction of wildlife habitats (0.045) (Hashemkhani et al., 2011).

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Hosseini et al. (2012) selected slope of terrain, aspect, hydrology, growing stock and soil type as influential factors for determination of suitability of forest area for construction of forest roads. Soil type was divided into three categories: stable, mid-stable and unstable based on rock type, slope, depth and drainage. These factors were presented as overlaid maps and analysed by using GIS.

Using of GIS tools and AHP analysis is very valuable method for developing a Decision Support System to determine maintenance priorities of forest roads on the basis of erosion risk and the evaluation of social value of roads (Pellegrini et al., 2013).

Optimal forest road density can be achieved by building new roads which have to be justified from the economic and technological aspect while considering the multifunctional usage of forest. The economic aspect means reducing the average skidding distance and skidding cost. Technological criteria demands usage of the DTM and Digital Elevation Model (DEM). Forest functions are graded during the elaboration of the Forest Management Plan (FMP) and are presented by the figures made by Forest Service. Forest functions are: protective, hydrological, climate, biotopic, hygiene and health, recreational, touristic, defensive, natural heritage protection, cultural heritage protection, educative, research, aesthetic, timber-production, hunting features etc. (Hribernik, 2013).

Density of forest roads depends primarily on growing stock and slope of terrain in analysed forest area. The growing stock is one of decisive factors which affects the quality and quantity of construction of forest roads. Forest accessibility for growing stock above 500 m³/ha and slope of terrain up to 30 % ranges to 120 m/ha for natural forests (Sokolović and Bajrić, 2013a).

According to Caliskan (2013), determination of suitability forest area for construction of forest roads is based on the analysis of slope, aspect, elevation, growing stock, hydrology, soil, bedrock and landslide sensitivity of forest area. Impact of these factors on suitability for construction was determined by using AHP method, and results of the analysis were as follows: slope with weight of 0.194, hydrology 0.172, bedrock 0.165, type of soil 0.164, growing stock 0.087, landslide 0.077, aspect 0.072 and elevation 0.069.

The decisive factors in defining of the relief areas are: altitude, terrain slope and ecological-vegetation type. Criteria for defining priority areas for accessibility are: terrain slope, technology, targeted average real skidding distance, skidding roads, allowable cut volume of timber for a management period (10 years), growing stock, age of stands and relief area. The chosen factors are analysed by multicriterial model which implies using of software Idrisi with tools Reclass, Fuzzy, MCE, MD Choice. AHP method was used because of the simplicity of pair comparison for the assessment of the importance and ranking of the criteria. The weights are relative values of every factor in a relation with the total number of factors which make parts in the analysis. The gained raster is divided into three categories: low priority, average level priority and highest level priority for accessibility (Lepoglavec, 2014).

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For strategic planning of the forest accessibility, it is needed to execute terrain classification according to slope, the use of the suitable system of forest exploitation, analysis of the primary accessibility and the analysis of the timber delivery, considering different relief areas (Đuka et al., 2015).

Firouzan and Abed (2015) conclude that planning of forest accessibility should be considered from the point of environmental factors and single silvicultural method of uneven aged structure of Shanderman area forests (Iran). Environmental factors are: slope, soil stability, aspect, regeneration of forests and growing stock. Weight of each affecting factor was obtained by using Multi Criteria Evaluation (MCE) and Expert Choice software.

Tampekis et al. (2015) evaluated impact of intensity of forest traffic by forest roads on environment and the ability of the environment to absorb the impacts caused by forest roads construction. This method refers to non-productive forests.

Environmental impact on the planning of forest roads was observed from the point of pollution of atmosphere by Green House Gases. Heavy machinery powered by diesel fuel was used for construction of forest roads and every phase of this job can be weighed in fuel consumption whose consequence is emission of Green House Gases in kg of CO2 per road unit. Total releasing of CO2 in the atmosphere is 27.54 kg/ m² of finished forest road, and mature beech forest can absorb 0.704 kg of CO2/ m² /year (Nenu, 2017).

The most common factors which were used in multi-criteria analysis are slope of terrain, type of soil and growing stock, and method which was used for this analysis is AHP.