The current study compared disturbances caused by two types of log-skidding machines, namely a rubber-tired skidder and a crawler tractor, on clay loam soil in forest. An extensive fieldwork was carried out to find out the impact caused by the combination of both machine types, traffic intensity (5, 10, 15, and 20 skidding cycles) and skid trail slope (0-15 % and >15 %) on soil compaction and forest floor after logging. The results showed that regardless of skidder type, bulk density of soil raised as traffic intensity and slope increased while the coverage of forest floor decreased. Within each traffic treatment soil compaction intensified with increasing skid trail slope, therefore significant differences in bulk density were observed between slope 0-15 % and > 15 %. Litter mass measured on the skid trail reached 2,012 kg ha-1 at the maximum (five passes on slope with inclination of 0-15 %) and 54 kg ha^-1 at the minimum (20 passes on slope > 15 %) for rubber-tired skidder, and 2,489 kg ha^-1 at the maximum (five passes on slope 0-15 %) to 470 kg ha^-1 at the minimum (20 passes on slope > 15 %) for crawler tractor. The results showed that the number of passes and slope and skidder type had strong effects on the intensity of soil disturbance. The results suggest that the rubber-tired skidder causes soil disturbance with lower traffic intensity than the crawler tractor. The dramatic increase of soil disturbance caused by the rubber-tired skidder may be associated with higher static ground pressures.

Keywords: bulk density, forest floor, skidder type, skid trail slope, soil disturbance.