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25%) were randomly chosen from 10 skid trails. The amount of soil displaced and ruts were measured using lateral profile of skid trail. Then the effective factors on soil disturbances such as longitudinal slope, soil texture, crown canopy and forest floor cover were separately measured in the studied plots. The results of regression analysis showed that there were significant differences between amount of soil erosion and longitudinal slope, soil texture, crown canopy and forest floor cover. The results from Pearson test showed that there was significant correlation between amount of soil erosion and longitudinal slope of skid trails, soil texture and forest floor cover (?= 0.01 and ?= 0.05), but there was no significant correlation between amount of soil erosion and crown canopy. The results of this research showed that by increasing longitudinal slope of skid trail, displaced soil volume and rutting depth increased. The sample plots in longitudinal slope class of >25% and average displaced soil volume of 5.3 m3 had maximum disturbance. Mean comparison test also showed that there were no significant differences in the displaced soil volume in the two longitudinal slope classes (0-15 and 15-25%), but with an increase in longitudinal slope (more than 25%), the average displaced soil volume increased.]]>
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13 passes of a Crawler Tractor Onezhets ? 110) and three levels of slope (<10%, 10%-20% and > 20%) were applied to assess soil disturbance. The soil samples from the depth interval 0-10 cm were collected with a soil hammer and rings. Results showed that dry bulk density, moisture content and total porosity were affected considerably by slope and traffic frequency of skid trails. Bulk density was drawing near to the critical value after 8 passes in the trail with the slope >20%; when the number of machine passes increased from 8 to 13 passes, the additional bulk density increment was negligible. Irrespective of traffic frequency, dry bulk density increased significantly in the slope >10% compared to the slope <10%; however there was no significant difference between slopes 10-20% and >20% . Minimum moisture content was measured as 27% on the skid trail versus 47% in the undisturbed area. A negative correlation was found between moisture content and dry bulk density. Total porosity was measured as a maximum 58% to a minimum 44% on the skid trail treatments, and 65% in the undisturbed area. Soil disturbance was extended dramatically on the treatments with slopes >20%, so dry bulk density on the treatments with 8 passes and slopes >20% (1.38 g cm-3) was significantly higher than on the treatment with 13 passes and slopes <10% (1.32 gcm-3). Results showed that slope >10% increased soil disturbance quite dramatically.]]>
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