| Summary: | Mechanized timber harvesting is cost efficient and highly productive. However, mechanized harvesting operations are often associated with several environmental problems, including soil compaction and disturbance. Soil compaction impedes air circulation between the soil and atmosphere, which in turn results in increased concentrations of CO<sub>2</sub> within soil pores. In this study, we investigated the impact of forest machine traffic on soil conditions to determine soil CO<sub>2</sub> efflux (<i>F<sub>c</sub></i>), and soil CO<sub>2</sub> concentrations (<i>S<sub>c</sub></i>). Field measurements included soil bulk density (BD), soil temperature (ST), soil water content (SWC), <i>F<sub>c</sub></i>, and <i>S<sub>c</sub></i> over a 3-year period at a specific thinning operation site (Hwacheon-gun) in the Gangwon Province of Korea. To assess the soil impacts associated with machine traffic, we established four machine-treatment plots (MT) characterized by different geographical and traffic conditions. The results revealed that BD, <i>S<sub>c</sub></i>, and SWC increased significantly on the disturbed track areas (<i>p</i> < 0.05). Furthermore, reduced soil <i>F<sub>c</sub></i> values were measured on the soil-compacted (machine disturbed) tracks in comparison with undisturbed (control) areas. Variations in BD, SWC, and <i>S<sub>c</sub></i> were significantly different among the four MT plots. Additionally, in comparison with undisturbed areas, lower <i>F<sub>c</sub></i> and higher <i>S<sub>c</sub></i> values were obtained in compacted areas with high soil temperatures.
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