Productivity models for cable yarding in Alpine forests

The authors tested the same modern mid-size tower yarder for uphill and downhill extraction. The yarding machine is a popular commercial model offering state-of-the-art yarding technology, including telescoping tower and full hydrostatic transmission. The machine was studied while harvesting selective patch cuts (gap cutting) in similar even-aged Norway Spruce stands, extracting logs between 3 and 6 metres long. The operation was carried out by the same experienced 3-man crew. Productivity ranged between 8.5 and 10 m3/h, including all delays, but excluding set-up and dismantle time. A set of regression equations for estimating machine productivity were calculated as a function of the main work conditions, such as yarding distance, lateral extraction distance, mean log size and number of logs per turn. Machine utilization was about 60%, which is consistent with previous studies. In general, cable logging is more complex and expensive than ground-based logging, which places steep terrain forestry at a general disadvantage in terms of pure harvesting cost. However, modern cable yarding technology can reduce this gap, and productivity models can assist users in refining their work technique, so as to maximize the productive potential of their machines.