Soil disturbance and quantification of machine traffic soil compaction associated with pushover logging

Pushover logging is a timber harvest system that involves pushing over trees with an excavator, thereby cantilevering the tree roots out of the soil. Pushover logging has the potential to cause above average levels of soil disturbance because of the soil disturbance associated with the uprooting process, and the increased trafficking of the harvest area by both the excavator and skidding machines. The purpose of this study was to quantify and describe the soil disturbance associated with pushover logging. Soil disturbance surveys were completed on two pushover-logged cut blocks in the Nelson Forest Region, near the towns of Golden (Colepitts), and Invermere (Mud Creek). The sites were chosen as representative of sites considered particularly sensitive to pushover logging harvest systems because of high compaction hazards. Soil core samples were taken for analysis of changes in soil physical properties, in four machine traffic disturbance types. Measurements of bulk density, total porosity, aeration porosity, and available water storage capacity were made. Soil disturbance is categorized as potentially detrimental if a negative impact on tree productivity, or on off-site forest resource values can be anticipated. Based on soil survey and laboratory results respectively, mean percent of harvest area occupied by potentially detrimental soil disturbance ranged between 11 % and 23 % at Colepitts, and 17 % and 2 % at Mud Creek. Determination of soil compaction in machine traffic areas, by hand- checking for changes in soil physical properties during the soil disturbance survey, was not a good indicator of compaction level as determined in the laboratory. Stump holes greater than 30 cm deep, created by the uprooting procedure, occupied 9.5 % of the Colepitts area, and 2.1 % of the Mud Creek area. This difference is attributed to stand and individual tree differences between the two sites. There were no significant differences (α = 0.05) found between disturbance types for bulk density, total porosity, and available water storage capacity measures. Aeration porosity measures showed significant differences between disturbance types at the 2 - 4 cm depth at both sites, and at the 6 - 8 cm depth at Mud Creek. At the Colepitts site, decreases in aeration porosity were associated with increases in machine traffic; at Mud Creek the highest aeration porosity values were at the surface in the heaviest machine traffic disturbance type. A lack of information on specific conditions at the time of harvest at Mud Creek make interpretation of the unexpected results difficult. At Colepitts, the levels of compaction measured are not of sufficient magnitude to forecast a reduction in tree productivity at this site in the future.Land and Food Systems, Faculty ofGraduat