Compaction of forest soils with heavy logging machinery

The paper investigated the effects of ground-based skidding on soil physical properties. For this purpose, soil disturbance following skidding was assessed for four levels of traffic intensity and three levels of slope gradients; each combination replicated three times. Soil samples were collected from the depth interval of 0-10 cm before and after traffic with a Timberjack 450C skidder in control areas and on skid trails. All soil response measures revealed detrimental compaction and porosity conditions in the skid trails, particularly on steep slopes >20%. The results clearly showed that most of the potential impact occurred after the initial passes. Substantial increases in bulk density appeared right after the first two skidder passes on steep slopes. Regardless of traffic intensity, however, dry bulk density and microporosity increased and total porosity, macroporosity, void ratio and soil moisture content decreased considerably regardless of slope gradient. Nonetheless, compaction effects and changes in soil physical properties were much more pronounced on steeper compared to more gentle slopes. We suggest that the dramatic increase in soil disturbance on steeper slopes >20% may be associated with the combination of increased load on the rear axle and lower skidder speed.