The runoff from the drainage of forest road surfaces and the rainfall at various road sections under various conditions were observed. A runoff model of water flowing on the forest road surface was made, and based on the obtained data, the coefficient of runoff on road and the length of runoff in roadside drainage areas was calculated by this model. From the results, the maximum length of runoff in roadside drainage areas was estimated to be 7.1 m for a main road which is located in a subordinate position on a hillside along a main valley and 2.6 m for a secondary road which runs from halfway up a hillside to the top of a ridge when the peak rainfall intensity was 1.1 mm/min. To obtain the factors which influenced on the coefficient of runoff on road surface and the length of runoff in roadside drainage areas, multiple regression analysis was performed. The depth of roadside drainage areas, accumulated rainfall for one hour and an index showing the location of roads were selected as factors in the multiple regression equation. These factors corresponded in both multiple regression equations.

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The amount of rainfall and soil loss from tractor logging roads were measured at 9 test road sections for two or three years after logging. Applying Universal Soil Loss Equation to estimate amount of soil loss, the soil erodibility factor was calculated. The correlation analysis showed that the factor related to the period after logging and the height of cut slope. A equation to calculate the soil erodibility factor was derived by multiple regression analysis. As a result, it became possible to more easily estimate the amount of soil loss from the tractor logging roads. To minimize the amount of soil loss from the tractor logging roads, the cut slope should be low.

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Recently, preventing damage to the landscape during construction of forest-roads has become a great concern. A plan is on foot to construct forest-roads for management and fire prevention in the Higasiyama mountains in Kyoto, and careful consideration must be given to the landscape because of the many famous historic sights around them. Therefore, we estimated the influence of three route plans on the landscape in advance using computer simulation. As a result, it was found that a route plan crossing the side of Kyoto city would have a minimum of influence on the landscape. In the computation, we gave different weight to the evaluation standards of influence on the landscape, costs of constructing forest-roads, potential slope failure and easiness of running by using AHP (Analytic Hierarchy Process). As a result of analyzing the three routes using these four evaluation standards, the best route plan can be determined.

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A swing yarder equipped with double winches was altered from a power shovel and was applied to the thinning process in steep ground. This yarder had two oil pressure drive winches on the boom. It can rotate itself and operate a boom or an arm while driving winches. As a result of this research, it was found that the set up and removal time were reduced and that the lateral yarding efficiency was relatively high. It was also determined that it was possible to unload trees directly on a forest road using a swing boom. The yarding efficiency was found to be the highest around the width of 40m in cutting areas, using the simulation which takes into account the time distribution of work elements. It was concluded that this yarder had oprational characteristics suitable for yarding on a low-structure forest road.

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A newly-developed mobile yarder altered from a power shovel was applied to thinning in a steep sugi (Cryptomeria japonica D. DON) stand. The physiological load of workers was investigated and it was found that the RMR estimated by heart rates was 0.4 for operating the yarder, 9.6 for loading, 8.0 for delimbing (in forest land) and 6.8 for bucking (on forest road) . Using the simulation based on these values of the RMR, we estimated the relationships between the width of cutting blocks and the energy consumption of workers. The result was that the energy consumption including setting up and dismantling of the yarder was minimum when the width was 62.2 m for the operator of the yarder, 41.2 m for a choker setter, 36.6 m for an unhooker and 41.6 m for a delimbing man. We also calculated the energy consumption of the workers for 8 hours and found that it was 1120 kcal for the operator of the yarder, 2588 kcal for a choker setter, 2606 kcal for an unhooker and 2929 kcal for a delimbing man. Compared with the energy consumption of an operator, that of the other workers was found to be far higher.

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Vehicle mobility tests were conducted on a crawler skidder and a feller-buncher on courses of gravel soil, sandy loam soil, and sandy loam soil with muddy conditions. We measured the relationship between the tractive effort and slippage, and obtained the experimental equations. As the result, the vehicles performed at the maximum tractive coefficient of 0.6-0.9 at 0.2 slippage. However, in muddy conditions, it lowered to 0.2-0.4. We believe the tests in muddy conditions are important in order estimate the performance of forest vehicles. The function of tilting the cabin worked effectively to improve the tractive performance. Slope ascending ability was estimated by the experimental equations. We also applied the WES method to evaluate the vehicle mobility, which indicated a possibility as a simplified testing method for forest vehicles by estimating the vehicles' mobility by calculating the surplus vehicle cone index.

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