Effects of aggregating forests, establishing forest road networks, and mechanization on operational efficiency and costs in a mountainous region in Japan

We investigated forest road networks and forestry operations before and after mechanization on aggregated forestry operation sites. We developed equations to estimate densities of road networks with average slope angles, operational efficiency of bunching operations with road network density, and average forwarding distances with operation site areas. Subsequently, we analyzed the effects of aggregating forests, establishing forest road networks, and mechanization on operational efficiency and costs. Six ha proved to be an appropriate operation site area with minimum operation expenses. The operation site areas of the forest owners’ cooperative in this region aggregated approximately 6 ha and the cooperative conducted forestry operations on aggregated sites. Therefore, 6 ha would be an appropriate operation site area in this region. Regarding road network density, higher-density road networks increased operational expenses due to the higher direct operational expenses of strip road establishment. Therefore, road network density should be reduced to approximately 200 m·ha−1 within average pre-yarding distances on which a grapple loader could conduct bunching without winching. With larger stem volumes a larger reduction in operational expenses occurred for the mechanized operation system compared to the conventional operation system. However, with smaller stem volumes, the operational expenses for the mechanized operation system were higher than for the conventional operation system. Therefore, the appropriate operation system and machine sizes should be determined based on stem volumes.