ABSTRACT:In this study, the effects of slope and traffic intensity on soil compaction, rutting and forest floor removal was evaluated on a skid trail in the natural forest of north of Iran. Combination of two levels of slope < 20% (SC1) and > 20% (SC2) and three levels of traffic (one, five and nine traffics) were studied. Treatment plots, with three replications, were established on the skid trail prior to skidding. The results of this study showed that all bulk densities were considerably higher in SC2 than in SC1 and average soil bulk densities were measured from 1.07 (g•cm -3 ) to 1.23 (g•cm -3 ) on skid trail and 0.91 (g•cm -3 ) in undisturbed areas. With the increment of traffic, soil compaction increased but there was no significant difference among the three levels of traffic frequency in SC1 whereas it was significant between one and five cycles in SC2. Greatest rut depth was measured as 12 cm at nine traffics in SC2, although increase of traffic density caused deeper rut depth at all slope treatments, but it was higher at the SC2 in comparison to SC1. Litter mass decreased considerably on the skid trail with the increasing in slope and traffic. No important difference has been detected between SC1 and SC2 in terms of Litter mass removal. These results provide clear evidence that soil disturbance on steep trail is intensified. 279Several studies have examined the relationship between soil disturbance and the associated number of loaded machine passes. The majority of previous studies investigated the effects of wheeled skidders on soil disturbance while a few studies assessed the impacts of steel tracked skidders whereas in many forest areas, particularly in steep terrain with large trees and high precipitation rates, these machines are likely to remain the most common type of skidding machine used.In mountainous and steep areas, the terrain slope is an important factor that affects operational efficiency, costs and erosion. It may also affect the soil compaction, so in planning forest operations and aligning skid trails the terrain slope may be an important consideration for protecting soil resources (Jamshidi et al. 2008).The objectives of this investigation were to (1) assess the soil disturbance after ground based logging by a steel tracked skidder and (2) determine the effects of slope on the soil disturbance in a skid trail. MATERIAL AND METHODSA field study was conducted at a Forestry Experimental Station of Tarbiat Modares University, located in a temperate forest in the north of Iran, between 36°31'56''N and 36°32'11''N latitudes and 51°47'49''E and 51°47'56''E longitudes, in February 2008. The elevation is approximately 650 m a.s.l. with western aspect, while the average annual rainfall of 1,308 mm has been recorded.The natural vegetation is a deciduous forest with dominant species of hornbeam (Carpinus betulus [L.]) and beech (Fagus orientalis Lipsky).Soil samples for detecting the soil texture were collected at ten random points from the top of the 50 cm deep soil profile from an undistu...

Reinforcement of skid trails with slash has been shown to reduce soil disturbances, but there have not been any studies documenting the mitigating effects following traffic of harvest equipment traffic on steep mountainous skid trails. The objective of this study was to quantify potentially mitigating effects of slash cover on soil compaction and rutting on skid trails in mountainous hardwood forests. The effects of the placement of no slash (bare soil), light density slash (7.5 kg m −2 ) and heavy density slash (17.5 kg m −2 ) in a skid trail following one, five, and nine machine passes on both gentle slopes <20% and steep slopes >20% in a downhill skidding operation by a steel-tracked skidder were studied. Bulk density and rut depth increased following harvest equipment traffic on both slope gradients. Compared to bare soils, soil bulk density was not significantly reduced by light slash density; however, soil bulk density was significantly reduced by heavy slash up to five machine passes on steep slopes. Light and heavy slash significantly reduced rut depth in both slope classes. The study revealed a high protective role of slash, particularly on steep skid trails. However, benefits of slash to mitigate soil compaction were limited to five passes, after which the slash deteriorated and only provided benefits against rutting.