Ecological Restoration of Compacted Soil Following the Application of Different Leaf Litter Mulches on the Skid Trail over a Five-Year Period

Ground-based skidding operations performed with heavy machinery have drastic effects on forest soils, which normally culminate in an increased soil bulk density and removal of the litter layer. We aimed to assess the efficacy of different tree species litter on the recovery of soil physical, chemical, and biological properties over a 5-year period in the Hyrcanian forests, northern Iran. Therefore, treatments included 45 combinations of five treatments (undisturbed area—UND, untreated trail or bare soil—U, and three leaf litter types: pure beech—B, beech-hornbeam—B-H, and beech-hornbeam-maple—B-H-M) replicated in three plots in three transects. Results show that the highest litter thickness, and concentrations of C and N in the litter were observed in the UND treatment. The litter C/N ratios were highest in the untreated trail (U; 27.52) followed by B > B-H ≈ B-H-M > UND treatments. The highest recovery of soil bulk density, total porosity, macroporosity, soil penetration resistance, and aggregate stability was observed on the B-H-M and B-H treatment followed by the B treatment. The highest recovery values of pH, C, N, C/N ratio, C and N sequestration recovery rates were observed on the B-H-M treatment, followed by the B-H treatment. Significantly higher values of available nutrients (P, K, Ca, and Mg), earthworm density, and biomass were found in the UND treatment followed by B-H-M ≈ B-H > B treatment, while the lowest amounts of available P, K, Ca, and Mg were detected for the U trail. The high-quality litter species (hornbeam and maple) allowed for better recovery of the soil organic matter and increased nutrient availability compared to the lower quality litter (beech). We can conclude that by applying the different litters on compacted soil, the measured soil properties were significantly improved at the B, B-H, and B-H-M treatments. Nevertheless, the soil properties following the B, B-H, and B-H-M treatments still demonstrated significant differences with the UND treatment, even over a 5-year period.