For an improved mechanized methods of logging, one of the most important issues is to consider whether skidding roads are systematically arranged in harmony with terrain features or not for a certain logging area. To realize such purpose, the characteristics of these road nets were analyzed theoretically and quantitatively by using some assumed geometrical models and field data practiced in felling sites. In this paper, we confined the skidding road network with tree structuers which was used in distributed hydrological modelling. Consequently, applications of stochastic branching process theory to skidding road networks were clarified. The distribution of bifurcation in these road nets was expressed by the relationship between the ratio of the numer of paths as segment which links origin to destination (t_j) and the ratio of the cumulative bifurcation points (g(t_j)). Namely, it could be expressed as an exponential equation by the α-th power of t, and where the exponent a is about 0.5-0.6. Also, the index (f-value), which described the arrangement of these road nets for a certain logging area, might be changed by the ratio of the minimum convex covering of the area within elongated skidding road nets per the whole logging area(k). From this concern, theoretical calculations were explained that the f-value was minimized when the ratio k was about 0.7. The minimum of the f-value, which was spontaneous skidding road nets with randomly distributed as tree structure, was about 1.57.

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We developed an autonomous crawler forwarder for the purpose of the improvement of the working efficiency and also safety of logging operations. The developed forwarder can travel with no driver by comparing self-position with the planning route that is input beforehand. The internal sensors that detect the azimuth and also the traveled distance recognize the self-position. Azimuth is detected by optical fiber gyro, using a geo-magnetic sensor to eliminate the influence of drift. Also, traveled distance is measured by integrating the axle speed. So, an error becomes big as it measures long distance by the influence of the slip. Because of this, we made the method that revises the control error by the external sensor, because it is difficult to extend the traveled distance using only the internal sensors. Permanent magnets and magnetic field sensor are used as the external sensor. Although there needs the labor that must lay down permanent magnets in strip road beforehand, it is possible to last autonomous traveling, by detecting the permanent magnets that are laid down separately.

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We reviewed articles on thinning and selective cutting published between 1994 and 1998. We used their information on high performance forest vehicles to analyze the relationship between the thinning method (including selective cutting) and production conditions. High performance forest vehicles were used for thinning on slopes with inclinations of less than 20 degrees. At felling, the method of thinning (line thinning, qualitative thinning, or selective cutting) depended on stand density. There were also clear differences in bucking (at the felling site or in the landing area) and hauling (skidding, forwarding, and hauling by grapple loader) depending on differences in stand density and skidding distance. Based on this analysis, we used stand density and skidding distance to evaluate the logging systems. The productivity of the logging systems considered to be optimal, which was affected by the inclination of the cutting area, ranged from 10-17m^3 person^<-1> day^<-1> for slopes under about 10 degrees to 6-10m^3 person^<-1> day^<-1> for slopes over about 10 degrees. In contrast, the productivity of the other systems was only 2-6m^3 person^<-1> day^<-1>. These results show that it is important to select the proper logging system for optimal production conditions.

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Optimizing layout method for mobil tower yarder was studied in a clear-cut logging operation. A time-study analysis of large size mobil tower yarder was used to estimate both the machine productivity and operating cost. Analysis indicates that optimizing method using neural network model can be used to improve productivity of tower yarder system. Further result suggest that system productivity of clear cut aerea is highest when operation site is constructed in small blocks, average 100 to 150m main line cable distance. Result indicates that enlargement of mobile tower yarder system sometime cause decrease of productivity, so large size mobile tower yarder must be only using as an alternate system in private forestry in Japan which has low forest road density.

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