A GEMCO tree-length forwarder was used to harvest pine from wet sites. It produced payloads of 26.9 metric tonnes with an average cycle time of 72 minutes. Hourly production averaged 32.9 metric tonnes per PMH while addition of the forwarder and a second loader to the system increased system cost by US$ 67.97/PMH. Use of the forwarder was less expensive than building all-weather roads to harvest timber in wet weather where volume accessed was relatively low or an extensive road network was required.
The paper deals with establishing the relationship between the traction factor and different parameters, such as the coefficient of rolling resistance, slip, some kinds of skidder efficiency, as well as other characteristics, and their change in correlation the tractive force and power. The analysis was made skidding different forms of wood: whole trees, tree length, long logs, logs and assortments. The traction factor is an exploitation parameter, the so-called net traction factor. It shows which part of the adhesive loading of a tractor can be used as draught. The general advice may be to perform skidding with minimum resistance but with maximum traction factor value.
Starting from the questions of the appropriateness of the term juvenile wood and the uncertainty in predicting its location in a given stem of a typical Northern American conifer, some predictions are made concerning the impact of the proportion of juvenile wood on bending properties of softwood lumber.
Results of a recent study which looks at the relative merits of proportion of juvenile wood and position in the tree stem as alternative indicators of bending strength of plantation White spruce lumber are used to expand the discussion. This work is related to changing harvesting and log transportation practices to those which make it possible to cut and segregate logs from tree stems in the relatively controlled environment of a sawmill rather than in the forest.
An analysis has been carried out of the skidding operations performed by the "Timberjack 380" forest tractor for an initial thinning of a Pinusradiata D. Don plantation. Knowing the maximum tractive force exerted by the tractor and allowing for the different resistances to forward movement (rolling friction, slope and load resistance), it has been calculated that the tractor can skid 10.1 m3 of material on a dry, compacted earth track, and 5.2 m3 on a wet track.
An examination of the various phases of the operations shows that total time per trip to be expressed by the following relation:
s„ su -aV
where su (speed of tractor without load) = 151.45 m/ min
a = 13.4352
V = volume transported
d = skidding distance.
On the basis of this relation and of the more general one expressing the output (P = 60 V/T), the maximum output was calculated for the "trip without load" phase and for the whole log removal phase. For the "trip with load" phase the maximum output, whatever the skidding distance, is obtained by transporting 5.636 m3, while, for the whole cycle, to achieve the maximum output the load should be 6.970 m3 over a distance of 800 m, and 8.180 m3 over a distance of 100 m.
From the analysis carried out and the results obtained, it is clear that the tractor, to ensure maximum performance, should transport material having a high unit volume, such as that obtained from clearcut-ting operations.