Effects of Skid Trail Slope and Ground Skidding on Soil Disturbance

The effects of traffic frequency and skid trail slope on dry bulk density, litter mass and rutting are examined. Treatments included a combination of four different traffic frequencies (3, 7, 14, and 20 passes of a rubber skidder) and three levels of slope ( < 10%, 10%-20% and > 20%.) The results showed that dry bulk density, rut depth and soil displacement increased with the increase of traffic frequency and slope, but floor coverage decreased. Within each traffic treatment soil compaction raised with the increase of skid trail slope, so that significant differences in dry bulk density were observed between slope of < 20% and those one > 20% . Bulk density has become quite close to the critical value after 14 cycles. With increase of the skidder cycles from 14 to 20, bulk density remained approximately constant. We observed soil displacement on the treatments with 7 cycles: rutting on the treatments started with 7 cycles and slope of > 20%. Soil disturbance increased significantly on slopes with > 20 % inclination with a dry bulk density of 1100 kg m-3 after 3 cycles compared to 830 kg m-3 on slopes < 10 %. In addition the forest floor mass on the treatments with 7 cycles and slopes of > 20% (437.6 kg/ha) was significantly (p < 0.05) lower than treatments with 14 cycles and slopes of < 10% (841.4 kg/ha.) Data suggest that disturbance increased earlier in the steep treatments than in less sloping conditions. The dramatic increase of soil disturbance on treatments with slopes of > 20% may be associated with increasing load on the rear axle combined with slipping on steep slope trail.