The objective of this research was to assess the effect of skidding machinery on soil physical and micromorphological properties. The different positions (control or non-traffic areas, left wheel track, right wheel track and log track) and two soil depths (0 - 10 and 10 - 20 cm) in three repetitions were investigated. The results showed that average soil dry bulk density in four positions and two soil depths were significantly different. Comparison of average total porosity percentage and soil saturated hydraulic conductivity revealed that there were significant differences in four positions and two soil depths. Soil thin section studies using Image Tool software showed that in compacted samples there was an increase in the number of vughs voids and channels voids were in low occurrence. Micromorphological studies showed that soil compaction caused void size to decrease. In compacted samples voids bigger than 10 μm were very rare and dominant voids size was 2 μm. In compacted samples soil structure were damaged and aggregates were compressed. Also soil matrix was compressed and microstructure was massive. Results from this study confirmed that skidding machinery had a significant effect on soil physical and morphological properties. These changes causes soil and environmental degradation due to reduction in water infiltration increasing soil erosion risk

ABSTRACT:The use of skidding machinery in logging operations causes destructive effects especially on soil but has many advantages such as extracting long and heavy logs, optimum use of useful logging time and absence of defect in wood production quality and thus an increase in the added value of wood. In this research compartment 40 of the second district of Nav-Asalem in northern Iran at an altitude of 1,050-1,450 m above sea level was chosen in order to assess the amount of displaced soil volume and depth of ruts due to the traffic of Timber Jack 450C rubber wheeled skidder along the skid trail. Therefore, the correlations between two independent variables, longitudinal slope and soil texture, with two dependent variables, displaced soil volume and average depth of rut, along the skid trail were examined after 20 passes of skidder machinery. The results of this research showed a significant difference between the longitudinal slope increase of skid trail and the amount of soil volume displaced (P < 0.001). However, there was no significant correlation between the mean rut depth and different classification of longitudinal slope along the skid trail. The highest measured rut depth was 22 cm and occurred in the slope class of more than 25%. There was no significant correlation between the amount of displaced soil volume and rut depth with changes in soil texture along the skid trail.

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ABSTRACT:In forest harvesting operations usually after using skidding machinery (skidders), traces of soil damage in the form of soil compaction and wheel and logs ruts can be seen in the forest soil. Soil bulk density, which represents soil compaction, decreases soil porosity, infiltration rate and aeration and these in turn increase runoff and water erosion in the harvested area. On the other hand, a decrease in soil aeration prevents root growth and decreases the vegetative cover. In this study the changes in soil bulk density and relative soil compaction due to a different number of wheeled skidder passes from stump to landing for two soil types (clay soil with high and low liquid limits, CH, CL) are analyzed. The results showed that the effect of skidder traffic on an increase in soil bulk density at sample locations was significant (α = 0.05). The range of soil bulk density increases in sample pits due to a different number of machinery passes was from 15.8% to 62.6% compared to the control area. The findings of this research showed that the interaction effect of skidder traffic and soil type on soil bulk density changes was not significant. Also the highest significant increase in soil bulk density occurred at the first 11 passes in skidding trails and from this number of passes onwards there was no significant difference in the soil bulk density increase in sample locations. 315In a study carried out by Jansson and Johansson (1998), the effect of wheeled and tracked machinery was studied on soil bulk density in silt loam soil in Sweden. The results showed that average bulk density increased 23% and 14% at 15 and 20 cm depth, respectively, after two passes of wheeled forwarder machinery (20 ton weight). The traffic of wheeled machinery at the first pass produces the highest compaction in soil and the following machinery passes have a lower effect, but overall soil compaction is produced which significantly affects the root growth (Hatchel et al. 1988). Studies by Burger et al. (1985) showed that the number of machinery passes significantly affects soil bulk density and the soil bulk density of top soil increases very rapidly in the first three passes and the following passes have a lower effect.Skidding operations are the most common way of causing soil compaction (Senyk, Craigdallie 1997). The skidding machinery is designed and manufactured in a way so that it can transport heavy loads in off-road conditions. Hence a major part of soil degradation occurs on skid trails and landings due to skidding operations (Heninger et al. 2002). Froehlich and Mcnabb (1984) came to the conclusion that the initial few passes of skidder have the highest compaction effect on soil. In other words, the initial 5 passes exceptionally increase soil compaction whereas the following passes cause less soil compaction. Gent et al. (1983) proved that in skidding operations using wheeled skidders, the severest compaction occurred at 10 cm depth of soil and the effect of compaction decreases with an increase in soil depth. In skidd...