Preserving Soil in Mountainous Plantations: Quantifying the Impact of Skidder Traffic on Soil Compaction and Moisture Dynamics in a Hyrcanian Poplar Plantation

Ground-based logging operations threaten soil sustainability in flatland plantations, yet their immediate impacts on the increasingly prevalent and ecologically sensitive sloped plantations remain a critical knowledge gap with urgent management implications. Following a clear-cut operation using a rubber-tired Caterpillar-555D skidder in a poplar plantation located in northern Iran, three distinct traffic intensity levels: low (3–5 passes), medium (8–10 passes), and high (15–20 passes) were analyzed. Skidding was performed under moderate soil moisture conditions, and post-harvest soil sampling for bulk density, total porosity, and gravimetric moisture content was conducted precisely one month post-operation. A randomized complete block design was employed, with three skid trails as blocks, each containing trail segments representing all combinations of the two SCs (<20% and ≥20%) and the three traffic intensities. Soil cores were taken from the wheel tracks at two depths (0–10 cm and 10–20 cm). Control samples were collected from adjacent undisturbed areas. Statistical analysis (three-way analysis of variance [ANOVA]) revealed highly significant (p < .001) main effects of traffic intensity, slope, and depth on all measured properties. Bulk density increased by 18%–34% in trafficked areas compared to the control, while total porosity and moisture content decreased by 15%–29% and 20%–40%, respectively. Significant two-way interactions showed that the detrimental effects of high traffic were exacerbated on steep slopes and in the surface soil layer. A strong negative correlation was observed between bulk density and both total porosity (r = −0.92, p < .01) and moisture content (r = −0.85, p < .01). Regression analysis indicated that bulk density explained over 70% of the variability in moisture content. The combination of high traffic intensity and steep slope caused the greatest soil degradation. These findings underscore the necessity for a management paradigm shift in foothill plantations, where preserving soil health must be prioritized as the primary, non-negotiable objective over short-term, productivity-focused metrics. Cite this article as: Hosseinzadeh, A., Naghdi, R., Tavankar, F., Khaledian, M., & Salehi, A. (2026). Preserving soil in mountainous plantations: quantifying the impact of skidder traffic on soil compaction and moisture dynamics in a Hyrcanian poplar plantation. Forestist, 76, 0022, doi: 10.5152/forestist.2026.26022.