Effects of timber skidding on soil physical properties and water retention of Dystric Cambisol loam soil in a natural lower montane forest in Southern Poland

Intensive forestry operations can cause soil compaction. This negatively impacts soil structure and water movement, particularly in mountain forest ecosystems. This study examined the effects of repeated passes of forestry machinery on the soil physical properties, pore system, and water retention characteristics of Dystric Cambisol loam soil in a natural lower montane forest in southern Poland. Soil samples were collected from control (non−compacted) areas and from machine wheel tracks exposed to different traffic intensities (1, 4, >6 passes, and permanent skidding trails) at two depths (0−10 and 10−20 cm). Bulk density, total porosity, pore size distribution, and soil water retention characteristics were determined using undisturbed soil cores and pressure plate measurements. Low traffic intensity (1 and 4 passes) did not significantly affect soil physical or hydraulic properties compared with the control. In contrast, intensive machinery traffic and permanent skidding trails caused a significant increase in bulk density and a reduction in total porosity, particularly in the 0−10 cm soil layer. These changes were associated with marked modifications in pore size distribution, including a substantial decrease in macropores and large mesopores (0.5−50 µm), which are essential for plant water availability. Alterations in the pore system were reflected in reduced field capacity, available water capacity, and unfavourable relative field capacity values, indicating impaired soil air−water relations under high traffic intensity. In the 10−20 cm layer, soil physical and hydraulic properties were largely unaffected by machinery traffic. The results demonstrate that repeated and intensive machinery passes during forestry operations pose a significant risk to soil structural integrity and water retention in mountain forest soils. Restricting traffic intensity and confining machinery movement to designated skid trails are essential measures to mitigate soil degradation and support sustainable forest management.