Evaluation of changes in soil physical properties 20 years after skidding operations

Soil degradation can negatively impact its physical and chemical properties over the long term. We investigated the natural recovery of physical properties of disturbed soils on an abandoned machine operating trail in a deciduous mountain forest in northern Iran. The machine operating trail hadn't been used for the last 20 years. Dry bulk density and total porosity were assessed for three levels of traffic intensity (light, moderate, and heavily trafficked trails) and two levels of slope gradients (gentle, <= 20%, and steep, >20%), in four different soil depths (0-10, 10.1-20, 20.1-30, and 30.1-40 cm) as well as in undisturbed (control) areas. Over the course of the 20-year recovery period, it was observed that in the depth intervals of 0-10, 10.1-20, 20.1-30, and 30.1-40 cm, trails subjected to heavy traffic on gently sloping terrain displayed mean values that exhibited an increase of 78%, 62%, 55%, and 47% in bulk density, respectively, and a decrease of 27%, 26%, 28%, and 27% in total porosity, respectively, when compared to undisturbed soil. In the case of steep slopes, analogous assessments indicated an increase of 82%, 69%, 39%, and 31% in bulk density, respectively, and a reduction of 28%, 29%, 26%, and 24% in total porosity, respectively, within the aforementioned depth intervals. However, in the case of lightly trafficked trails situated on gentle slopes, there was a discernible amelioration in surface soil compaction. Our findings consequently suggest that the natural recovery of soil physical properties in the study area extends beyond the examined timeframe of twenty years.