Commercial Thinning in Small-Diameter Spruce-Fir Stands-Production and Cost of Skidding and Skyline Yarding, With and Without Prebunching
- Seymour, Robert S.
Cooperative Forestry Research Unit, The University of Maine
- Gadzik, Charles J.
Three experimental systems for commercial thinning mature spruce-fir stands, involving prebunching with a radio-control led winch followed by either skidding or yarding with the Smith Timbermaster skyline yarder, were compared to a conventional two-man skidder operation. Regression equations derived from time-study data, which predict total cycle time from winching/yarding distance and number of trees per turn, are presented. A general procedure for calculating costs per cord from the study results is described and used to compare the four systems in terms of production and cost.
In spite of rapid cycle times, skyline operations, with or without prebunching, were significantly more expensive per cord than skidder-based systems, due mainly to light loads and higher labor costs. Winch prebunching improved skidding production dramatically by reducing cycle times and increasing loads, but the savings were only slightly greater than the cost of the prebunching operation. The conventional two-man skidder system effectively carried out the thinning operation with no more damage than the two-stage prebunching system, due in part to the prior layout of skid trails. The effect of varying tree size on total thinning cost is analyzed for each system; piece rates and stumpage values are presented for a range in tree size between 8 and 30 trees per cord.
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