In this study, yarding operation is modeled as a system which includes some independent objects, and operational efficiency was simulated on a computer using this model. In this model, we can estimate operational efficiency when there are changes in some parts of objects, or when some imaginary situations are set. In the simulation, the carriage was imaginarily changed to the one that had radio-controlled self-locking mechanism. As a result, the yarding efficiency was estimated to be 2.4 times higher than before, and the difference of efficiency between the estimation and the real operation is 4.9%. It was concluded that this object-oriented model could simulate a real operation pretty well, and could estimate approximate operational efficiency when some parts of system changed. Using this simulation, we can choose the optimal system of operations by trial and error without a real operation.

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The mechanized forest operations using the high efficient forest machinery are being practiced throughout the country. The forest road network will be constructed densely for the introduction of machinery and the execution of operation. The unstable soils produced along the roads will become the source of sediments. For 10 months, the authors observed the output of soils from the collapsed slopes. The surface runoff from the newly collapsed slopes was larger than the older ones and was inversely proportional to the area of slopes. Output of total and finer soils were relative to the total rainfalls. The tendency of soil loss by the same runoff per unit area did not change very much even after 2 years from the collapse of slopes. The particle size distribution of the transported soils depends on that distribution of the materials of the slopes and on the total soil loss. Nevertheless the increase in the ground cover ratio with the lapse of the time, the soil loss continued without much changes. The appropriate measures must be taken according to the mutual positions of the slopes and the streams and to the conditions of the slopes such as the gradient and the forest floor covers.

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Recently, high performance forestry machines have come into very wide use in Japan. These forestry machines are wheeled typed base machines except a tower-yarder. On the other side, looking at cable-typed forestry machines, the number of cable yarding systems is decreasing while those of the tower-yarders and self-propelled carriage systems are increasing. About eighteen hundred self-propelled carriage systems are used in Japan for 1995. In this paper we discussed on the trends of these forestry machines and on the spread trends and operation system of the self-propelled carriage system. This machine has been used from the area of Kyushu since 1983, and spread to the Gifu-Prefecture and Shizuoka-Prefecture and then to Iwate-Prefecture. We studied for the case of Tenryu District. It results that we can expect the average yarding productivity is 18.5〜35.7m^3 per set.

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Colluvial soil or sediment from cut slopes often stops traffic on forest roads and it is troublesome to remove it too often. The objectives of this study are to quantify such soil dropped by rainfall or by freezing and fusion and to forecast seasonal and annual variation of it based on the results of measurement. In this study, we made three research plots on cut slopes whose slopes were 63.4, 55.0 and 48.0 degrees and observed the volume of colluvial soil or sediment. As a result, the soil volume of 48.0-degree slope decreased year by year while the others did not. In the fourth year, the soil volume of 48.0-degree slope reached 127kg while that of 63.4-degree slope reached 476kg, which was about 3.8 times as much as that of 48.0-degree slope. We used the analysis of variance to analyze relationships between the soil volume and the independent variables such as frequency of freezing and fusion, amount of rainfall and slope angle. As a result, all the independent variables were found to be significant at the 1% level. It should be noted that the contributing portion of frequency of freezing and fusion was 25.8% and was by far the highest among the three factors. Time series data on the volume of colluvial soil was separated into three portions such as TC (Trend and Cyclical component), S (Seasonal variation) and I (Irregular variation) using the EPA method (Economic Planning Agency method). The model to forecast the future volume of colluvial soil on a cut slope was subsequently made using TC and S components. The results showed that the model forecast seasonal and annual variation of such soil with high accuracy.

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