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A comparison of productivity for whole tree, tree length, and log length skyline thinning in 35 year old Douglas-fir stands of western Oregon

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  • Whole tree and tree length thinning are two alternatives which are likely to be more productive and may prove to be more cost effective than conventional log length thinning. The purpose of this study was to evaluate and compare log length, tree length, and whole tree thinning techniques in terms of productivity and harvesting costs. The thinning operation took place in a second-growth Douglas-fir stand [Pseudotsuga menziesii (Mirb.) Franco] (average dbh = 12.8") using a small skyline yarder (28' tower, 120 HP) in a gravity return configuration. The treatments were defined by the amount of work done by the faller prior to yarding. Log length implies that felling, limbing, bucking and topping occured at the stump. Tree length indicates that trees were felled, limbed and topped only, and finally, whole trees were felled only prior to yarding. A rubber-tired cable skidder was used to swing material from the landing chute to a processing area. Here the skidder operator Forest Engineering presented on April 14, 1983 completed any limbing and bucking which was necessary. He then sorted and decked the logs prior to loading. During log length thinning, logs were either cold decked in front of the yarder or swung with the skidder to a loading deck. Detailed time studies were used to evaluate the felling and yarding operations for each of the three thinning techniques. Multiple linear regression was then used to develop predictive models for felling and yarding work cycles. An analysis of the delays on this study made it possible to separate out delays which were affected by a particular thinning technique, rather than having a single prorated delay time as is usually done. By combining results from the regression and delay analyses, estimates of productivity for each thinning technique were obtained. Finally, harvesting costs in dollars per cunit at the loading deck were generated and used to compare log length, tree length, and whole tree thinning. Results indicated that where cold decking is feasible and will not overly hamper the operation it will probably still be the cheapest alternative since a skidder is not required. The cost per cunit for this method was $8.24 or 11% cheaper than its closest competitor, the whole tree system. However, where cold decking is not feasible, as is often the case on steep slopes with narrow roads, the whole tree technique will be the most cost effective alternative. It has a per cunit cost which is $10.06 or 12% less expensive than conventional log length thinning with a skidder swing. The advantage to the whole tree system results primarily from transferring limbing and bucking from the stump to the landing where it is not only done more efficiently, but also reduces operator idle time on the skidder swing.
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