INTRODUCTION Ground-skidding system is the process of moving trees or logs from the cutting site to a landing or roadside where they will be processed into logs or consolidated into larger loads for transport to the processing facility or other final destination. In the Hyrcanian Forest located in north of Iran, extraction with ground-skidding equipment is the most common system and also the one that tends to cause the greatest environmental problems. Iran is considered to be amongst the low forest cover countries (LFCC), with the forest cover of 7.4% of the country area. Hyrcanian Forest has a total area of 1.85 million hectares comprising 15% of the total Iranian forest and 1.1% of the country ’ s area [1]. The combination of the timber type and topography limit harvesting mechanization to perform transport operations. Rubber-tired skidders are used on the more gentle slopes and on skid roads on steeper terrain. Crawler tractors are used on steeper topography to skid direct to the landing. In steep terrain that is not accessible by ground-based machines, Felled trees are processed by chain saw into logs and then hauled by mules [2]. Regardless of the type of skidding equipment used, machines with an appropriate size and power configuration for the operation should be selected. Many countries restrict ground skidding to slopes of less than 30 percent (17°) except for short distances [3]. In north of Iran, this limit is 25 percent [4]. Many studies were carried out on productivity and cost of harvesting and logging operation and factors affecting the machine performance [5, 6, 7, 8, 9, 10, 11, 12, 13]. Bjorheden and Thompson [14] mentioned that the knowledge gained in the study of forest work is used to improve operational efficiency through better planning and control of future work. The purpose of forest work study is to provide a method for developing the knowledge needed to make good decisions in this complex environment. Akay et al. [15] studied the productivity of mechanized harvesting machines such as: skidder, feller- buncher, harvester, loader and forwarder in Turkey. Abeli [16] analyzed and compared the production rates and costs of three forest road construction machines (Ford County 1164 tractor, D4D and D6D Caterpillar bulldozers). Result showed that differences in production rates were attributed mainly by the type and the size of the machine, driver’s working experience and the nature of the terrain side slope. Productivity and cost of two skidders, Timberjack models 460 and 660, were evaluated while operating in a loblolly pine plantation performing a clearcut harvest in the Southeastern US. Productivity without delimbing was 46.7 tones per PMH for the model 460 and 51.7 tones per PMH for the model 660. Cost per tone was $1.70 for the model 460 and $1.90 for the model 660 [17]. In north of Iran, Sobhani and staurt [2] evaluated the harvesting system with using Clark 66BDS wheeled skidder in first time and until now a couple of studies on productivity and cost of skidding machines have been reported by several researchers. Feghhi [18] assessed two mechanized forest harvesting systems including Madil 046 in high lead system and combination of both Clark 66 BDS wheeled skidder and komatsu D65 crawler tractor in Shafaroud Forest. Naghdi [19] studied optimum road density in tree length and cut to length systems using Timberjack 450 C and mentioned that the productions of Timberjack with and without delay were 13.6 and 17.1 m 3 /h, respectively. Because of high investments in forest utilization, planning and management for work and machines are very important. Of very important issues in forest utilization are the finding of proper machines and combination of them based on time study and skidding models. Machines in wood transportation Productivity and cost of wheeled skidder in Hyrcanian Forest Meghdad Jour GHOLAMI * Baris MAJNOUNIAN Department of forestry and forest economicsFaculty of Natural Resources University of Tehran, Iran * Corresponding Author Received: May 14, 2008 E-mail: mjgholami@gmail.com Accepted: July 09, 2008 Abstract Wood transportation from harvesting unit to the roadside landing devotes the most expensive pertaining to logging operations. Heavy machines in wood transportation are imported tools; however they have very high hourly costs per hour and depreciation rates which oblige us to find appropriate transportation methods (approaches) for reducing costs. This research aims at evaluation of the theory in which more production results in reduction in the cost. The research also attempts to offer an analysis of production and cost of a skidder (Timberjack 450C) thorough an application in Educational and Experimental Forests of Kheirood. In the ap- plication, the time elements and effective factors in turn time of skidding operation were investigated based on 44 turns. The results indicated that the total production with and without delays in skidding with Timberjack 450C skidder was 8.22 and 8.88 cubic me- ters per hour, respectively. The cost of skidding using with and without delays was $7.41 and $6.86 per cubic meter, respectively. Key words: Wheeled skidder, Timberjack 450C, productivity, cost, time study. International Journal of Natural and Engineering Sciences 2 (3): 99-103, 2008 ISSN: 1307-1149 www.nobel.gen.tr