EFFECT OF SKID TRAIL COMPACTION ON A VOLCANIC SOIL IN CENTRAL OREGON

A skid trail in the Ochoco National Forest, Oregon, was examined to assess the degree of compaction that had occurred as a result of traffic during log harvesting. The soil, classified as a Lithic Cryorthent is a sandy loam derived from rhyolitic and tuffaceous colluvium. Measurements of bulk density and shear strength were made at five positions across the trail and two locations in undisturbed soil. Cores were taken to measure bulk density, moisture content, and moisture retention. Compaction resulted in increases in bulk density of up to 25%, in shear vane strength up to 157%, and in cone index up to 220% along with a decrease in pore space greater than 10 mu m of 69%. Bulk density, vane shear, and penetrometer measurements were found to be highly correlated.