The deeper the lane, the stronger the changes: Soil physical properties of forest skid trails and their spatial distribution

In highly mechanized modern timber harvest, forest soils are wheeled by heavy vehicles on skid trails. This leads to structural changes in the soil. The aim of this work was to quantify the soil physical properties of skid trail lanes of different depths (0-10, 10-20, 20-30 cm). Between 2017 and 2021, 18 existing skid trails in a spruce stand in the low mountain range Solling (southern Lower-Saxony, Germany) were examined from a soil physical point of view after repeated use with a harvester (25 Mg total mass) and a forwarder (35 Mg). Undisturbed soil samples were taken at six soil depths in the lane, in the adjacent edge area and in the nearby undisturbed forest soil. In addition, disturbed samples were collected as well for analysis like soil texture. The dry bulk density increases with lane depth and, on average, reaches maximum values in the middle of the lane. This decreases in the edge areas. Significant differences between the treatments can be determined up to a sampling depth of 35 cm. The saturated hydraulic conductivity is lowest in the deepest lanes. With the exception of the sampling depth of 50 cm, this also applies to the porosity, which can primarily be explained by a decrease in the coarse pores. A trend can be derived from the results: The deeper the shape of the lane, the more it deviates from the unwheeled comparison area in terms of its physical soil properties.