Effects of Skidder Passes and Slope on Soil Disturbance in Two Soil Water Contents

Skidding operations induce changes in soil physical properties, which have the potential to impact soil sustainability and forest productivity. Our objective was to investigate the effects of traffic frequency, trail slope, and soil moisture content on soil compaction, total porosity and rut depth. Treatments included a combination of three different traffic intensities (3, 7, and 14 passes), three levels of slopes (< 10%, 10–20% and > 20%), and two levels of soil moisture content (18% and 32%). Soil bulk density and total porosity were measured as 0.75 g cm and 71%, respectively, along the undisturbed area. The results show that bulk density, total porosity and rut depth on skid trails were significantly affected by traffic frequency, skid trail slope and soil moisture content. As the skidder passed, skid trail slope and soil moisture content increased, increasing significantly the average bulk density. Bulk density draws near the critical value after 7 and 14 passes, respectively, at higher and lower soil water content. At each moisture content, the increase of slope > 20% caused a significant increase of the average bulk density. Total porosity on the skid trail was measured from minimum 45% (14 passes and slope > 20%) to maximum 58% (3 passes and slope < 10%) at higher soil water content, and minimum 49% (14 passes and slope > 20%) to maximum 68% (3 passes and slope < 10%) at lower soil moisture content. Rut depth was recorded at 7 and 14 passes at high and low soil water content, respectively, and it increased with the slope. The results show that slope and moisture content had strong effects on soil disturbance.