Surface Soil Disturbance Under Conventional and Small-Scale Mechanized Timber Harvesting Systems: A Comparative Case Study in South Korea

As the environmental sustainability of forest management has become an increasingly important consideration, incorporating environmental performance into timber harvesting operations has grown to be correspondingly critical. This shift is reflected in a growing move away from large-scale clear-cutting toward smaller-scale harvesting operations. To conduct such small-scale harvesting efficiently, mechanized systems have increasingly been introduced into practice, yet how these systems affect the soil environment relative to conventional harvesting methods remains insufficiently understood. In the Republic of Korea, where steep, mountainous terrain predominates, this knowledge gap is particularly consequential, as the conventional (chainsaw felling and excavator-based woodgrab extraction) system often produces spatially diffuse and severe surface soil damage. This study compared surface soil disturbances between conventional and small-scale mechanized (SSM) harvesting systems across three slope gradient classes (moderate, <20°; steep, 20–25°; very steep, >25°) at five harvesting units in the Republic of Korea. Disturbance was assessed at total of 2046 systematically distributed grid points using a four-class visual disturbance protocol, with continuous disturbance surfaces derived by inverse distance weighting (IDW) interpolation. The results indicate that SSM systems shift the pattern of disturbance rather than uniformly reducing it. On moderate slopes, SSM (grapple saw felling and clambunk skidding) reduced the proportion of severe, area-wide disturbance but concentrated deep rutting along fixed skid trails, producing significantly deeper ruts than the conventional system. On the steep slope, the SSM system pairing mechanized felling with swing yarder extraction substantially reduced both the extent and the severity of disturbance relative to the conventional system by eliminating in-stand machine travel during extraction. On the very steep slope, no paired conventional unit was available for comparison, but the SSM system using a small tower yarder resulted in a notably low level of surface disturbance. These findings suggest that the soil-protective benefit of SSM systems may depend on how machine traffic is distributed during felling and extraction, offering evidence to guide slope-specific system selection for environmentally sound timber harvesting.