In Canadian boreal forests, harvesting with protection of advance regeneration requires the creation of an intensively used network of skid trails. In this context, the effects of repeated skidder passes on soils were studied in terms of rut depth, the amount of displaced material in the trails, and soil bulks density. Two types of soil were studied: sands and clays. The factors that helped to explain the observed amount of soil disturbance were the number of skidder passes, the amount of wheel slippage, soil density, the soil's penetration resistance, and the soil's shear resistance. The results of the study indicated that the effects of skidder traffic on soil properties stabilized after a few skidder passes on sands, whereas the effects on clay soils continued to increase with an increasing number of skidder passes.