. 2012. Recovery of soil bulk density, porosity and rutting from ground skidding over a 20-year period after timber harvesting in Iran. Silva Fennica 46(4): 521-538.Ground-based skidding can have detrimental effects on soil properties trough soil profile disturbance and compaction that can persist for decades. We investigated the recovery of physical properties of disturbed brown soils on four abandoned downhill skid trails in a deciduous mountain forest in northern Iran. The most recent skidding operations had taken place 1-5 yrs, 6-10 yrs, 11-15 yrs, and 16-20 yrs ago, providing a 20-year chronosequence with four 5-year recovery periods. For each recovery period, mean values for soil bulk density (BD), total porosity (TP), macroporosity (MP), soil moisture content (SM), and rut depth (RD) were assessed for three levels of traffic intensity (Primary (PS), Secondary (SS) and Tertiary (TS) skid trails) and two levels of slope gradients (Gentle (G) and Steep (S)) and compared to those in undisturbed (control) areas. Over the 20-year recovery period, PS trails on gentle slopes exhibited mean values that were 35-42% (BD), 3-7% (SM), and 13-19 cm (RD) greater and 18-24% (TP) and 19-28% (MP) lower compared to undisturbed areas; on steep PS trails, values were 40-46% (BD), 2-13% (SM), and 13-21 cm (RD) greater and 23-27% (TP) and 28-35% (MP) lower, respectively. While RD and SM recovered, 20 years was not long enough for the other physical soil properties, particularly on steep slopes. To minimize soil disturbance, skidding should be confined to areas with gentle slopes and alternative harvesting methods such as cable yarding should be used where slope gradients exceed 20%.

We investigated the long-term effects of ground-base skidding on residual damage severity on the healing of residual damaged trees in forests of northern Iran twenty-years post logging operation. Characteristics examined included wound size, location, severity, height from ground level, number of wound on the damaged tree stems, and distance of damaged tree from centerline of the skid trail on a 8-meter distance alongside the abandonment skid trail. There were some crucial changes in the characteristics of the wounds on the damaged trees stems, which have been investigated on the high traffic intensity and the low traffic intensity. Results showed that an average amount of damaged trees alongside skid trails, which were 100% inventoried, were 18.83%. Results also confirmed that based on the available measurements of a twenty year period, it is too early to make any definite conclusion about how long it will take for occlusion of wounds on tree stems to fully heal from timber operations.

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Abstract& Key message Skidding operations significantly influenced soil physical properties up to a 2-m distance from the wheel ruts in a forest ecosystem. The most significant changes in soil properties were identified within a 0.5 m to 1 m transitional zone. & Aims The main purpose of this investigation was to determine how far into a forest stand changes in soil physical properties were evident due to skidding operations. & Methods Treatment plots with three replications included combinations of four distance zones at 0.5 m intervals (0 to 2 m in distance) on both sides of skid trail edges to the forest, three slope gradient levels were applied (gentle <10 %, moderate 10-20 %, steep >20 %) and two levels of traffic intensities 20 and 40 passes (with a rubber-tyred skidder, model HSM 904). A total of 576 soil samples were used in this study. & Results Results showed that the physical properties of soil were significantly changed by each traffic intensity in the first distance zone, where the slope was >20 % compared to soil changes at a slope of <20 %. The largest changes in soil properties were identified at 0.5 m transitional distance zones for a slope gradient >20 % after 20 and 40 skidding cycles. & Discussion Dry bulk density values reached its maximum levels in the first 0.5 m from the skid trail on slopes >20 % after 40 skidding cycles.

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