Soil Compaction from Logging with a Low‐Ground Pressure Skidder in the Oregon Coast Ranges

Increased bulk density of a clay loam soil on logging skid trails in the Oregon Coast Ranges was most highly correlated with the logarithm of the number of turns with a low‐ground pressure (FMC) skidder. The surface 15 cm of soil was impacted more by uphill than by downhill yarding. Downhill skid trails with three or fewer turns had small increases in bulk density, usually < 10%. The regression relationship ( r 2 = 0.411; S y·x = 23.16) developed for the 7.5‐cm depth indicated that nine turns with an FMC skidder would increase soil bulk density approximately 25 and 45% for downhill and uphill yarding, respectively. After approximately 18 turns with an FMC skidder, the predicted bulk density increase at the 22.5‐cm soil depth was 25% (±5% at α = 0.1). Modified 10‐blow Proctor tests slightly overestimated increases of soil bulk density on high‐use downhill skid trails. The 15‐ and 10‐blow Proctor tests very closely estimated these density increases for the 7.5‐ and 15‐cm depths, respectively, for uphill skidding.