Influence of ground-based skidding on physical and chemical properties of forest soils and their effects on maple seedling growth

The main purpose of this study was to evaluate the effects of skidding operations on the physical and chemical properties of soil as well as root and height growth of maple seedlings. Treatment plots with three replications included combinations of three levels of traffic frequency (three, eight, and 16 passes of a rubber-tired skidder Timberjack 450C) and two levels of trail gradient (≤20 and >20 %) to quantify soil disturbance and corresponding seedling growth. Significant differences between undisturbed areas and machine trail areas of bulk density (0.75 vs. 1.26 g cm⁻³), total porosity (70.6 vs. 50.4 %), macroporosity (44.5 vs. 18.5 %), microporosity (26.1 vs. 31.8 %), moisture content (50.0 vs. 31.3 %), and forest floor biomass (3498 vs. 1271 kg ha⁻¹) were strongly related to the level of traffic frequency and the trail gradient. Similarly, skidding caused significant reductions in the amount of soil OC (by 41 %), concentrations of nitrogen (53 %), phosphorous (28 %), potassium (31 %), and soil acidity (40 %) compared to undisturbed areas. Finally, germination rate, root length, and stem height of seedlings were inversely related to compaction. Physical and chemical soil properties are often significantly impacted by skidding operations, depending on trail gradient and traffic frequency, which resulted in restrictions to seedling growth.