Soil deformation, which consisted of the share band and high degree of material movement, caused by a semi-legged vehicle, was analyzed by EDEM (Extended Distinct Element Method). EDEM can analyze uncontinuous materials as it represents soil as independent particles. EDEM can also analyze continuous materials by introducing the pore-springs to represent surrounding fill materials. The adaptation of EDEM was examined with soil and a pantographic leg. In the simulations of experiments with Toyoura sand, the values of reaction forces of sand without the rolling friction were significantly smaller than the measured values, but by introducing the rolling friction, those of reaction forces became similar to the measured values because the moments were transmitted among particles. The effect of the criteria for failure of pore-springs on the soil deformation was examined. The phenomena such as soil particles not falling into the holes dug by the leg could be expressed, when the proper criteria were set up in the simulations. As for the effect of the compaction in soft and hard soil, the difference in reaction forces could also be expressed.

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We investigated what factors determined the necessity of affiliate structures for slope-failure prevention, such as retaining walls, on low-standard forest roads and the degree of the effect of such factors. The factors to be analyzed were selected with reference to related research on slope failure. We focused on the reduced cost of low-standard forest roads as an advantage, as well as the possible disadvantages because of the requirement of affiliate structures for slope-failure prevention, which may be costly. The analysis was carried out with field-obtained data in order to define the characteristics of such roads that do and do not have such structures. As a result, the following factors were found to have strong effects: slope inclination and drainage areas as factors with regard to terrain, road curvature as a factor related to road geometry, and rock-soil composition and geological structures as factors related to soil and geological properties. All factors having a strong effect produced the typical effects as described in the related studies.

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In this study, a change in the number of multi-functional forestry machinery in Japan was predicted using growth-curve models. Logistic-curve and Gompertz-curve were fit into the number of machines during fiscal year 1988-1997, and the AIC of both models were compared for validity evaluation. The model parameters were estimated by nonlinear regression analysis (maximum likelihood method). As a result of estimation, the predicted level of machine saturation was 2,000 by Logistic-curve model and 2,900 by Gompertz-curve model. Gompertz-curve model was chosen as a proper model because the AIC was fewer. The following attributes were expected to increase; "harvester" in machine type, "Kanto and Chubu" and "Kinki, Chugoku and Shikoku" in region, "other cooperatives (support centers for the security of forest labor etc.)" for machine utilization in ownership. All in all, the rate of machine increase was predicted to level off, so we should make more efforts to utilize machines effectively than to increase in number.

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Logging operations of private forest on a small scale forestry need efficient logging operation system. Analyses of logging operation systems on a small scale were performed according to Ehime Prefecture data that were about thinning operations from 1981 to 1990. Main operation systems were yarding mini-forwarder, human power, yarder and self-propelled carriages. The average of productivity was 1.10m^3/man・day. The highest productivity was yarding operation with self-propelled carriage, mini-forwarder, yarder and human power in order. Moreover, the average of production cost was 16,779 yen/m^3, and yarding operation with mini-forwarder was the cheapest cost of production, and then self-propelled carriage, yarder, human power respectively. A theory of quantification was applied and the factors which have an influences on logging operations were analyzed. The most influencing factor in logging operation was logging operation region, the next factors were difference of logging operation system, DBH, cutting ratio, average gradient (degree) and logging distance respectively.

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To estimate the influence of site qualities on profitability, an economic evaluation based on an empirical yield table for an artificial forest of Cryptomeria japonica, is developed. In this evaluation, 6 cases (3 levels of site quality and 2 levels of planting density) have been simulated respectively, and a normal forest is assumed. Each stand which forms a normal forest have a area of 100 meters square with 100m road in the uppermost part. Commercial thinning can be carried out after 26〜27 years old in stands with high site quality, while commercial thinning cannot be carried out until final cutting in stands with low site quality. Final cutting can be carried out in stands with high site quality after 45 years old, while final cutting cannot be carried out in stands with low site quality until 80 years. The cause of these differences is the shortage in utilizing volume in stands with low site quality. The utilizing volume in stands with high site quality is 3.18 times higher than that in stands with low site quality. Next, years of break-even point are simulated on the condition that a wage level fluctuates. The result of this simulation indicated that in case of the wage level is low, profitability from stands with low site quality would be close to the one of high site quality. As the wage level increases, profitability from stands with low site quality decreases rapidly. As a consequence, artificial forests must be managed separately with a viewpoint of site quality.

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