Operation time, cost, and productivity of a flow harvesting system were compared with a disjointed system, utilizing system dynamics models. The models were developed using the cycle time information obtained for four processes: tree felling with a chain saw, hauling with a long-reach grapple, skidding with a grapple, and bucking with a processor, in a forest harvesting system at a thinning site operated by a logging contractor in Hyogo Prefecture, central Japan. The results of simulations indicated that the operation time of the flow system was about 60% lower than that of the disjointed system, but its operation cost was about 40% higher. In the flow system, the net working rate of each process after the felling process declined, which increased the cost. A further simulation in which the standard deviation of cycle time of the felling process doubled indicated that the operation time of the flow system was 9% higher than that of a model with a constant cycle time in the felling process. These results indicate that the disjointed system should be used especially in cases where the cycle time varies greatly, such as immature operation or qualitative thinning.

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This study aimed to develop a thinning system using an excavator with long-reach grapple for prehauling operations. We examined the effects of thinning method, prehauling direction, terrain and road condition on productivity. The maximum productivity of labor was 9.0m3/man-hour under the conditions of line thinning, down-hill prehauling, slope of 23°, short prehauling distance of up to 33m, road width of 3.5m and timber volume of 0.32m3/tree, which was about 1.5 times higher than ordinary thinning at 5.9m3/man-hour under similar conditions. Using a small winch on the top of the arm, the maximum slope prehauling distance from thinning trees to roads exceeded 70m, and the productivity decreased only 10%. The productivity for downhill prehauling was about 1.6 times higher than for uphill, and the maximum prehauling distance for downhill was 6m longer than for uphill. The productivity for the road width of 3.5m was about 1.6 times higher than for 3.0m. On the other hand, the terrain had little effect on productivity. Consequently, this machine offers high productivity for both ordinary and line thinning, although a road structure that can support the heavy weight of this machine is needed.

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The assumption that beech (Fagus sylvatica) cutting is more dangerous compared to spruce (Picea abies) and fir (Abies alba) trees, due to its complex and asymmetric tree crown characteristics, variety of branch dispositions, lengths, and thickness, and often swept trunk, was tested. The accidents, which occurred to concessionaire workers in Slovenian State Forests, in the period 1999-2005, were analysed. Out of 999 forest accidents, 528 of them occurred during cutting, out of which 475 occurred during cutting of beech, spruce and fir trees. The index I_k, i.e. risk ratio of accidents with reference to cut volume, and the index I_d, i.e. risk ratio of the number of trees cut as a reference to the accident, showed that the accident risk during cutting of beech trees was 1.1 times (I_d) and 1.5 times (I_k) higher than that for spruce and fir. According to both indices (I_d and I_k), the risk was higher during wedging (1.3 and 1.9), back-cutting (1.6 and 2.3), and bucking and cross-cutting (2.0 and 2.9), respectively. When clearing the lodged trees and delimbing, the risk was according to index I_k higher with beech trees at 1.4 and 1.2, whereas it is lower at 1.0 and 0.8 under index I_d, respectively. In general, the I_k index showed higher accident risk than I_d. The reason for this could be explained by the long work durations of beech trees in spite of lower volume per tree of beech trees which has short assortments. The results are useful for selecting safety work measures in terms of preliminary safety education and work preparation for control and work organization.

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