Shape of Skidder Productivity Function for Ground Based Skidding System in Caspian Forests

Cut-to-length (CTL) timber harvesting technology currently accounts for approximately 90% of Caspian forests. The technology involves felling, branching, cross-cutting, and then the skidder carries the logs to a landing, where the timber is temporarily stored, sorted and assembled for transportation to the mill. Cut-to-length systems typically require less labor, less access road construction, and fewer landing areas than other ground-based systems such as whole tree harvesting and also lead to more efficient wood recovery. In Caspian forests of Iran, harvesting and extraction systems are assigned to specific harvesting sites on the basis of inherent terrain class, silvicultural consideration, stand characteristics and access to the sites for the extraction of the timber. In the region, ground based kidding is the most common form of extraction of harvested timber. Forest management in Iran faces many challenges, and most forest land is governmentally held. Harvesting equipment needs to be as productive as possible. For example, efficiency of skidding operation is dependent on having a skilled operator, mechanically sound equipment and a sufficient volume of logs to be skidded. But skidding efficiency is also influence by the stand condition and harvesting prescription. Information on the productivity, cost and application of harvesting machines is a key component in the evaluation of management plans for the rehabilitation and utilization of Caspian forests [1]. Logging and transporting optimization are becoming key areas for improvement. Improving operational efficiency through better management is one way that the Iranian forest industry can enhance its competitive position. Due to the higher initial cost of mechanized harvesting machines, larger diameters and crowns of hardwoods, and the relatively steep terrain in Caspian forests, Wheeled skidders is still the most commonly used machines in the region, on the other hand research efforts for modeling and planning improvements to the wood chain are increasing. Essentially, all Caspian forests in the Iran are harvested with cut-to-length system. Few previous studies addressed techno-economic analysis of skidding operation in Caspian hardwood stands under different harvest conditions. Jones et al. [2] conducted a time study on a 60-acre tract with three thinning treatments in northern West Virginia. The three treatments were defined as 45%, 60% & 75% of the residual stocking. The harvest comprised of manual felling with a chainsaw. Time studies showed that hourly felling production increased while skidding productivity decreased from the treatments 45 percent, to 60 percent, and to 75 percent of residual stocking. Regression equations were later developed based on the above time-study data [3], which can be used for estimating production rates and costs for similar thinning operations.