Soil displacement during ground-based mechanized forest operations using mixed-wood brush mats

The goal of this research was to examine the mitigating effect of brush mats on soil disturbance caused by off-road traffic of forest machinery, specifically how brush quantity affects rutting and soil displacement in a cut-to-length (CTL) harvesting operation. A field test was performed to analyze the effects of brush mats of varying quantities on the severeness of soil disturbance. At the project test site, located in a mixed-wood stand on silty soils in southern New Brunswick, Canada, two machine operating trails were covered with five different brush amounts (0, 5, 10, 15, and 20 kg/m2). A Logset F-series forwarder with a total loaded mass of 35,800 kg completed three traffic cycles (each consisting of one loaded and one unloaded pass) plus one additional empty pass to simulate the passage of a harvester. The resulting soil disturbance was assessed by determining the area of displaced soil in cross sections of trail segments covered with brush mats of 5, 10, 15, and 20 kg/m2. Results indicated that indent areas of individual tire tracks were between 0.0 and 0.6 m2 when covered by 15 kg/m2 brush mats and normally <0.2 m2 when covered with 20 kg/m2 mats. Relative to the no brush (0 kg/m2) treatment, 5, 10, 15, and 20 kg/m2 brush mats offered reductions of indent areas of 0.0, 14.3, 71.4, and 90.5%, respectively. ANOVA results indicated that brush mats of 15 and 20 kg/m2 along machine operating trails significantly reduced soil disturbance caused by timber harvesting equipment when compared to trail segments with no brush mat. Because regression trees were able to predict minimum indent area (0.0 m2) and rut depth (3.8 cm) based on soil moisture and brush amounts, extending CTL forest operations into soil moisture conditions beyond 50% is not being recommended in this study.