Changes in forest landscapes resulting from road construction have increased remarkably in the last few years. On the other hand, the sustainable management of forest resources can only be achieved through a well-organized road network. In order to minimize the environmental impacts of forest roads, forest road managers must design the road network efficiently and environmentally as well. Efficient planning methodologies can assist forest road managers in considering the technical, economic, and environmental factors that affect forest road planning. This paper describes a three-stage methodology using the Delphi method for selecting the important criteria, the Analytic Hierarchy Process for obtaining the relative importance of the criteria, and finally, a spatial multi-criteria evaluation in a geographic information system (GIS) environment for identifying the lowest-impact road network alternative. Results of the Delphi method revealed that ground slope, lithology, distance from stream network, distance from faults, landslide susceptibility, erosion susceptibility, geology, and soil texture are the most important criteria for forest road planning in the study area. The suitability map for road planning was then obtained by combining the fuzzy map layers of these criteria with respect to their weights. Nine road network alternatives were designed using PEGGER, an ArcView GIS extension, and finally, their values were extracted from the suitability map. Results showed that the methodology was useful for identifying road that met environmental and cost considerations. Based on this work, we suggest future work in forest road planning using multi-criteria evaluation and decision making be considered in other regions and that the road planning criteria identified in this study may be useful.

© iForest -Biogeosciences and Forestry IntroductionForests support a lot of ecosystem services, including primary products, secondary products, water supply, hydrological regulation, environmental purification, soil formation, soil conservation, biodiversity conservation, recreation, etc. (Gios & Clauser 2009, Gaodi et al. 2010. One of the main objectives of forest management is the sustainable utilization of natural resources (Mataji et al. 2010). Forest road planning plays an important role in forest management and logging practices. Roads are essential structures to provide access to the forest for wood production and logging ). On the other hand, road construction and log skidding are the most expensive and destructive operations in the forest environment, leading to soil compaction and increasing surface runoff and soil erosion along the skidding path. Therefore, the viability and profitability of operational forest management plans are deeply influenced by road construction and maintenance costs, as well as the road network structure (Kirby et al. 1986). A large area of forest is destroyed during road construction, provoking not only economic losses, but also changes in the environmental conditions (Jadczyk 2009). Road construction in forest may also cause biodiversity loss as a result of habitat fragmentation (Hui et al. 2003, Smulders et al. 2009, Da Silva et al. 2010, making forest communities more prone to impoverishment and depletion. As the high density of forest road network will lead to the excessive economical and environmental costs, forest road managers have to carefully evaluate and optimize the forest road network density for minimizing the total costs and environmental impacts of these infrastructures. Average log skidding distance is an important component to evaluate the quality of forest road network, and should be considered for computing the optimal forest road network density (Zhixian & Zhili 1997). Matthews (1942) was the first who developed a two dimensional model for skidding distance, with assumptions of flat terrain condition, regular road distribution, and provided that logs are carried out on the shortest path to the nearest road. Segebaden (1964) improved the road spacing model by introducing network and transport correction factors. Heinimann (1997) reported that the above mentioned assumptions do not apply in mountainous conditions with sloped terrain, and introduced a slope correction factor to compute the real skidding distance.Road technical specifications and wood extraction methods are two main factors affecting optimum road spacing and density, aimed to minimize the total cost of roading and skidding (Rowan 1976, Naghdi & Mohammadi Limai 2009). Moreover, the timber volume to be harvested is an important factor affecting the quantity and quality of forest road network density. Sedlak (1983) calculated road spacing with regard to volume of annual growth and reported lower average road spacing in parts of forest with higher annual growth and larger harvesting volume.There...

Though it is well known that vegetation affects the water balance of soils through canopy interception and evapotranspiration, its hydrological contribution to soil hydrology and stability is yet to be fully quantified. To improve understanding of this hydrological process, soil water dynamics have been monitored at three adjacent hillslopes with different vegetation covers (deciduous tree cover, coniferous tree cover, and grass cover), for nine months from December 2014 to September 2015. The monitored soil moisture values were translated into soil matric suction (SMS) values to facilitate the analysis of hillslope stability. Our observations showed significant seasonal variations in SMS for each vegetation cover condition. However, a significant difference between different vegetation covers was only evident during the winter season where the mean SMS under coniferous tree cover (83.6 kPa) was significantly greater than that under grass cover (41 kPa). The hydrological reinforcing contribution due to matric suction was highest for the hillslope with coniferous tree cover, while the hillslope with deciduous tree cover was second and the hillslope with grass cover was third. The greatest contributions for all cover types were during the summer season. During the winter season, the wettest period of the monitoring study, the additional hydrological reinforcing contributions provided by the deciduous tree cover (1.5 to 6.5 kPa) or the grass cover (0.9 to 5.4 kPa) were insufficient to avoid potential slope failure conditions. However, the additional hydrological reinforcing contribution from the coniferous tree cover (5.8 to 10.4 kPa) was sufficient to provide potentially stable hillslope conditions during the winter season. Our study clearly suggests that during the winter season the hydrological effects from both deciduous tree and grass covers are insufficient to promote slope stability, while the hydrological reinforcing effects from the coniferous tree cover are sufficient even during the winter season.

Forest roads play an important role in providing access to forest resources. However, they can significantly impact the adjacent soil and vegetation. This study aimed to evaluate the effects of road geometry (RG) on the chemical and biochemical properties of adjacent soils to assist in environmentally friendly forest road planning in mountainous areas. Litter layer, canopy cover, soil organic carbon (SOC) stock, total nitrogen (TN), the activity of dehydrogenase (DHA), and urease (UA) enzymes at a 0–20 cm soil depth were measured by sampling at various distances from the road edge to 100 m into the forest interior. The measurements were done for three road geometries (RG), namely straight, curved, and bent roads, to ensure data heterogeneity and to reflect the main geometric features of the forest roads. Analysis of variance (ANOVA) showed that the effects of RG on the measured variables were statistically significant. Spearman’s correlation test clearly showed a strong positive correlation between environmental conditions, SOC, TN, DHA, and UA for given RGs. Based on piecewise linear regression analysis, the down slope direction of the straight and the inside direction of bent roads accounted for the lowest and highest ranges of ecological effects, respectively. The results of this study contribute to our understanding of the environmental effects brought about by road geometry, which can be important for forest road managers when applying the best management practices.