effects of ground-based skidding using wheeled skidder timberjack 450c on forest soil physical properties (case study: gorazbon disrict, kheyrud forest)

forest harvesting operations for extracting of forest products in these trails, causing extensive damage in a wide range of soil and its productivity every year, therefore it is necessary to research about degradation of soil properties should be down. the aim of this study was investigate changes in the skid trails soil physical characteristics due to wheeled cable skidder traffic by measuring soil texture, bulk density, porosity and soil penetration resistence. for this purposes, 311 and 319 compartments of gorazbon district in kheyrud educational and research forest were selected. this study was conducted in a completely randomized factorial design and treatments consisted of two slop (uphill and downhill), three levels of skidder traffic intensity such as low intensity (less than 3 passes), moderate (3 to 7 passes) and very large (more than 7 passes) and two soil depths (0-10 and 10-20 cm).the results showed that machine traffic intensity and skid trail slop statistically had significant effects on soil compaction. soil compaction and penetratin resistance will increase with increasing of machine traffic, but the largest percentage increase observe in initial passes (less than 3 times) although subsequent passes change this factors, but its trend is not significant, also soil compaction is greater than in the uphill skidding of downhill skidding and in the 0-10 cm soil depth greater than 10-20 cm. hence, we concluded that skidding operation should be planned in slope lower than 20% and uphill skidding (higher than 10%) should be excluded from ground-based logging systems.