Comparison of Two Skidding Methods in Beech Forests in Mountainous Conditions

Investigation of different skidding methods was done in the northwestern part of the Republic of Srpska, in the area of municipality of Ribnik. Two skidding methods were compared, assortment (short-log) method and half-tree length method. Investigation was conducted in four sample plots, in two compartments of beech forests. The difference between sample plots was based on working methods and mean DBH of felled trees. The aim of this research was to compare the productivity and costs of assortment method, which is currently dominant in the forestry of the Republic of Srpska, and half-tree method as a modification of tree length method. Skidding was done with forest skidder LKT 81T in winter conditions with almost no snow. Time and work study was performed. Different statistical methods were used for investigating the influence of different variables on the work process. Multiple linear regression analysis showed that work operations mainly depend on distance and load volume in both methods. Loaded drive depends on distance and load volume. Strength of correlation relationship is similar in both methods. These findings are in compliance with other investigations that can be found in literature. The results showed higher productivity and lower costs in half-tree-length method than in the assortment method. For the skidding distance of 250 m and similar stand conditions, the productivity is 42.29 m3/day for assortment method (A1) and 50.50 m3/day for half-tree length (A2) method, and 62.93 m3/day (B1) and 83.64 m3/day (B2), respectively. Costs are 17% (A2 against A1) and 40% (B2 against B1) lower for half-tree length method when all other conditions are the same. The difference in cost increases with the increase of the difference of the average piece volume of the two skidding methods