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Operational prebunching: a logger's application to reduce skyline thinning costs Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_projects/6395wd353

Graduation date: 1980

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  • In the Pacific Northwest, loggers are faced with the problems of changing from logging old growth to second growth. This is due to the shrinking old growth timber supply and increased entry into the· second growth stands. Beuter (1 980) indicated that in western Oregon 70.2 percent by volume of the softwood timber presently being less than 1 2.9 inches {53.09 centimeters)1 dbh, with 37 percent being less than 12.9 inches (32.77 centimeters) dbh. Tedder (1 979) states that by the year 2075 the average diameter for all western Oregon owner groups will fall from 23 inches (58.42 centimeters) to 1 4 inches {35.56 centimeters). The trend to harvesting smaller timber will require development of harvesting techniques that can handle small wood more efficiently. Small wood is defined (Aulerich 1 975) as a tree under 20 inches (50.8 centimeters) dbh or logs averaging less than 1 00 board feet (0.71 cubic meters) in volume. In-small wood harvesting, corrnnercial thinnings pose special problems. Thinnings are used as a silvicultural treatment to enhance the growth of the residual stand. In skyline thinnings, yarding logs laterally into the corridors is a time consuming activity, es­pecially pulling slack during lateral outhaul and finding enough logs within reach of the chokers to build an optimum turn (near maximum payload). Aulerich (1 974) found lateral yarding accounted for 46 percent of the total yarding time. Sparse log density and small log size make building an optimum turn difficult. Yarding logs laterally through standing timber is also a prob-lem. There are frequent, time-consuming hangups requiring resetting the chokers or dropping off part of the turn. Reset time can be expensive, because the yarder stands idle and its hourly operating costs are high. In previous research at Oregon State University, prebunching and swinging has been suggested as a means for reducing yarding costs in skyline thinning operations. Prebunching and swinging differs from full-cycle (conventional) yarding in that in prebunching and swinging, logs are moved from the unit to the landing in two yarding cycles. The first cycle is the prebunching cycle, where the logs are laterally yarded to. decks along the skyline corridor. The second yarding cycle is the swinging cycle, where the logs are yarded from the prebunched decks to the landing. In full-cycle yarding logs are yarded in one cycle which includes the lateral yarding and swinging. By prebunching with a low investment yarder, it may be possible to increase the utilization of an expensive yarder and there­by reduce total yarding costs.
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