Impacts of off-road traffic on soil physical properties of forest clear-cuts: X-ray and laboratory analysis

Due to the great year-round demand for forest products, off-road forestry traffic occurs even when the ground is susceptible to soil compaction and rutting. We investigated the impacts of repeated passes with a laden forwarder (34?Mg) on the soil physical properties of two clear-cuts on stony till soils in northern Sweden. Core samples (n?=?71) were collected from the top 5?cm of mineral soil in and beside wheel tracks, after six passes with the forwarder. Soil physical properties were quantified using classical soil physical analyses and X-ray tomography. The hydraulic conductivity was 70% lower in the wheel tracks than in the soil beside. The X-ray image analysis indicated that this was due to the smaller total volume and lower connectivity of structural pores (φ?>?60?µm). Total porosity was 24% and 12% lower in the tracks at the two sites respectively, and mean bulk density was 1.39?g?cm^?3 in the tracks, compared to 1.13?g?cm^?3 beside them. To conclude, traffic changed the soil physical properties in a way that may lead to longer periods of high water content in the wheel tracks, increased risk of surface runoff and insufficient aeration for optimal seedling growth.