Chronological variation in soil density and vegetative cover of compacted skid trails in clearcuts of the western Oregon Cascades

Graduation date: 1981This study evaluated the recovery of compacted soils on logging\ud skid trails in clearcuts of the western Cascade Mountains of Oregon.\ud Soil types included clay, clay loam, silt loam, loam, sandy loam\ud and loamy sands. Sites ranged in age from five to 38 years since\ud harvest and 370 to llOOm in elevation. Soil bulk density, measured\ud with a nuclear density probe, was used to characterize compacted\ud soil conditions. A number of soil, vegetation and site variables\ud were studied to determine possible cause and effect relationships\ud with compaction recovery.\ud Study design consisted of nine sites with nine plots at each\ud site. Plots were classed by level of use with three plots in each of\ud the low, medium and high use level classes. At each plot, measurements\ud of bulk density were taken at the skid trail center, skid trail track and the less-disturbed area adjacent to the skid trail.\ud Determination of vegetative cover was also made at these locations.\ud Depths of measurement for bulk density were 5.1cm, 15.2cm and 30.5cm.\ud No statistical difference of bulk density values was detected\ud between skid trail use-level classes. A similar result was found\ud for the vegetative cover variables. Bulk density values on the\ud skid trail center and skid trail track were statistically similar.\ud However, density on the skid trail track (and center) were greater\ud than those of the less-disturbed area ([alpha]= 0.05). When the data\ud were stratified by site age, the skid trail track still retained\ud greater bulk densities than the less-disturbed area on the 38 year\ud old site. No trends in bulk density changes were observed over\ud time.\ud Interaction between herbaceous cover and overstory cover\ud decreased the usefulness of these variables for correlation with\ud recovery. However, shrubs indicated a reduction of percent cover\ud on skid trails up to 21 years since harvest, but not after\ud that time. This was the only variable measured which indicated\ud possible skid trail recovery.\ud Regression analysis was performed using the bulk density\ud difference between the skid trail track and less-disturbed area as\ud the dependent variable and several soil, site and vegetative variables\ud as independents. Multicolinearity among the independent variables\ud was high and when coupled with the variable nature of the bulk\ud density data, produced inconsistent results