Assessment of Soil Parameters In Response To Repeated Wheeling

Within the wood supply chain, timber harvesting plays a crucial role, especially with the growing importance of the bioeconomy. The increased utilization of efficient, fully mechanized harvesting systems, however, raises concerns regarding their potential negative impacts on soil health and functions, particularly on and in the vicinity of skid trails. This study focused on the effects of repeated wheeling by a fully mechanized timber harvesting system on various soil properties in a mixed stand dominated by Picea abies located in Upper Austria. The study site is located on Stagnic Cambisol formed on silty Molasse sediments, partly covered with Pleistocene gravel and loess deposits. To assess these logging effects, we utilized four portable wheel load scales to estimate the surface contact pressure per single wheel of both empty and loaded machinery for each pass. Soil rutting was evaluated using terrestrial laser scanning and Structure from Motion (photogrammetry). Penetration resistance was measured using an Eijkelkamp Penetrologger. Both were assessed before and after the harvester passed, twice during forwarding and after extraction was completed. Undisturbed soil cores for the determination of soil moisture content, bulk density, total porosity, and C/N ratio were sampled initially, after the harvester pass, and after the final pass of the forwarder (twelve loaded passes). Control measurements and samplings were performed before the harvest for comparison purposes. Preliminary findings indicate a minimal incidence of soil rutting, with more pronounced effects observed on skid trails with higher clay content. The peak of penetration resistance occurred at a soil depth ranging between 5 and 10 cm. The harvester pass exhibited a comparable effect (2.4 MPa; control = 1.2 MPa) to the cumulative passes of the forwarder (3.7 MPa). Further laboratory examinations on bulk density and C/N ratio are expected to confirm these observations. Consequently, the low soil moisture content of 10 Vol.–% during timber harvesting contributes positively to soil stability at the end of a pronounced drought period. The preliminary results emphasize the strong impact of the initial pass of the harvester.