Evaluation of changes in soil physical, chemical and biological properties 25 years after skidding operations in Kheyrud forest

Soil compaction is a widespread problem in forestry due to the use of heavy machinery for timber harvesting and the lack of attention to soil conditions in harvesting operations. Therefore, the present study was conducted to investigate the natural recovery process of compacted soil properties after skidding operations in Kheyrud forest. Four abandoned skid trails with different ages (3, 10, 20 and 25 years) were selected with three replications at the forest area. In each of them, three traffic intensity classes and three slope classes were specified and sampling were done at the wheel track at depths of 0-10 and 10-20 cm of soil. The results showed that 20 years after the skidding operations, bulk density, penetration resistance and microporosity were 8.4%, 27.4% and 50.44% greater and TP, MP and SM were 1.96%, 17.1% and 4.58% lower than the undisturbed area, respectively. 20 years after skidding operation, the values of pH, EC, C, N, Available P, K, Ca, and Mg, earthworm density and biomass were lower than the undisturbed area, respectively, and value of C/N ratio was higher than the undisturbed area. High traffic intensity (H3) and slope classes of 20 - 30% (C3) in the 3-year skid trail had the greatest impact on soil properties, that indicating greater changes and longer recovery of soil properties in these treatments. The consequence of this study indicated that recovery of soil chemical properties is longer than biological and physical properties, so that complete recovery of these properties takes more than 25 years.