Compaction of a silty clay loam forest soil was compared for 2 types of log-skidding equipment, a rubber-tyred skidder and a flexible-steel-tracked skidder. Experiments involved the loaded skidders traversing marked laneways at zero, 2, 4, and 10 passes. Compaction was quantified in terms of 3 parameters: (1) bulk density to 25 cm depth measured gravimetrically, (2) penetration resistance using a field penetrometer, and (3) saturated hydraulic conductivity using a field rainfall simulator. Results showed no substantial difference in soil bulk density between the experimental treatments, regardless of skidder type or number passes. Penetration resistance of the traversed laneways was significantly higher than the surrounding undisturbed areas; however, there was no difference between skidder type. Rainfall simulation showed that the saturated hydraulic conductivity of all treatments was strongly reduced by trafficking, although this did not differ with skidder type. The results from this study highlight the dangers in assuming that reduced machine static ground pressures will automatically lead to reduced soil impacts. It is important to note that while this study did not find differences between the 2 skidder types when operated in a similar manner, differences in the operation of the two skidders may also influence impacts on soil properties.
Soil Bulk Density and Porosity Changes due to Ground-based Timber Extraction in the Hyrcanian Forest