2023 Volume 105 Issue 4 Pages 110-117
To evaluate soil compaction by vehicles on skid roads in a Todo fir (Abies sachalinensis) plantation in Bibai, Hokkaido, we established road and control (forest) sections on a survey road 1 year after construction. Soil penetration resistance (Nc) was measured in both sections for a period of 4 years, and dry bulk density and porosity were measured for 3 years. The soil compaction index (SCI), which reflects the compaction of surface soil, was calculated for each survey year using the Nc values. The median Nc value of the road section was higher than the median value of the control section. The median SCI for soil depths of 0-10 cm decreased over time, whereas the value for depths of 0-0.3 m decreased from the first to third year after construction but remained unchanged thereafter. The dry density in the road section was higher than the density in the control section from the second year onward, and the porosity of the road section remained low. In the control section, dry density and porosity remained nearly constant throughout the study period. The longitudinal change in soil compaction indicated different tendencies depending on the measured soil physical properties. These results demonstrate that the skid road surface remained strong throughout the 4-year period, although the degree of compaction decreased by the third year.
