Impacts of a fully mechanized timber harvesting system on soil physical properties after a pronounced dry period

Abstract

Within the wood supply chain, timber harvesting plays a crucial role, especially with the growing importance of bioeconomy. This study focused on the effects of a fully mechanized timber harvesting system using a harvester and forwarder on various soil properties in a mixed stand dominated by Picea abies located in Upper Austria. Using portable wheel load scales, we measured the load per wheel of both the empty and loaded forwarder. We analyzed soil rutting and penetration resistance before and after two harvester passes, after two and nine forwarder passes, and at the end of the harvesting operations (n_passes = 18). Soil samples were collected using steel cylinders before and after the harvester, and at the end of the harvesting operation. We measured soil water content, bulk density, total porosity, and the C/N ratio. The results showed a mean rut depth of 13 cm after the harvesting operation was completed. Soil deformation began in predisposed areas (e.g., roots and stumps). Maximum penetration resistance occurred at 10–15 cm, highlighting the substantial impact of both harvester and forwarder at this depth. Harvester effects on penetration resistance were noticeable down to 40 cm, while forwarder effects extended beyond 80 cm. Significant changes in bulk density appeared only after forwarder passes. Low initial water content (12 Vol.–%) enhances soil stability, reducing impacts compared to winter harvesting under the high–moisture conditions. Harvesting at the end of a dry period (e.g., late summer) is a viable alternative for protecting soil physical properties.