Locating log depots and routes of forest roads using graph theory (Case study: Designed roads in ‎district two of Bahramnia forestry plan)‎

This study aimed to select the lowest cost graph through locating cost-benefit depots (nodes) and road segments (links) to complete the road network in the second district in the Bahramnia forestry plan in Golestan province. In 2017, the value of each link and node was calculated for 36 candidate roads in cutting areas. The total cost of skidding for each node was estimated using a model with variables of consumed time for each skidding cycle, rate of skidder rent, number of skidding cycle, number of logs (trees marking list), skidding and winching distances as well as the length of logs (2.8 meters for industrial logs). After determining the cost-benefit nodes, their connections were provided by links. The cost of construction for each link was calculated using a model with various variables includes the length and longitudinal gradient of links, the side slope of terrain and unit cost of link construction. However, the total harvesting cost was obtained based on the total cost of links and nodes. Our findings indicated that by using the graph theory and the cost minimization approach, the most appropriate nodes and links were located close to marked trees and low slopes. Therefore, the proposed second graph was chosen as the optimal variant. The total skidding cost of depots and construction cost of optimal graph were 262.14 Rial and 17.73 Rial m-1, respectively. The total length and harvesting cost of the optimal graph were estimated at 532 m and 9697.14 Rial, respectively.