Skid trails are a major management-induced disturbance in temperate forest ecosystems with considerable impact on soil ecological processes that are so far poorly understood. In German forests, skid trails comprise 10 – 20 % of the forest area that is potentially affected by soil compaction through heavy machinery. We systematically investigated the influence of skid trails on physical, chemical, and microbiological soil parameters at 84 paired plots across four Central European forest types. In low mountain forests with steeper topography, skid trails had more drastic effects than in lowland forests. Skid trails in low mountain areas showed a decrease in the C to N ratio of microbial biomass (MBC/MBN), as well as increased microbial (MBC/SOC) and enzyme activities leading to faster carbon turnover (lower C/N, EOC/EN) and increased CO₂ losses (CO₂/SOC) from the soil. The overall effects of the skid trails in lowland forests were small. On base-poor soils, we found an increase in the MBC/MBN ratio, while skid trails in base-rich lowland soils showed a reduction in CO₂/SOC, suggesting a proportional increase in soil carbon storage. Regardless of region-specific effects, the relative increase in the bulk density of the fine soil was identified as a ‘golden trait’ that determined the effects of skid trails on many soil parameters, as shown by negative correlations with SOC, N, MBC, MBN, MBP, MBC/SOC and CO₂/SOC and positive ones with the activities of certain hydrolytic enzymes.

Synthesis and Applications: Our data clearly showed that carbon conversion processes and soil respiration leading to significant carbon and nutrient losses increased significantly on skid trails in low mountain regions with relatively steep slopes, which was in sharp contrast to lowland sites. The strong context dependence of our findings suggests that the mapping of soil conditions in terms of slope, substrate and moisture with high spatial resolution is mandatory to assess the vulnerability of sites to soil compaction by heavy machinery. Based on such vulnerability analysis, negative impacts can be minimized through the designation of permanently fixed skid trails, the technical adaptation of vehicles (e.g., wide base tyres) as well as careful planning and timing of management operations that should be restricted to dry weather and soil moisture conditions or periods of frost.

The data was collected as part of the BiCO₂ project, a large-scale study of biodiversity and carbon storage along a forestry intensity gradient at four different forest sites in North Rhine-Westphalia, Germany. This partial dataset was used to investigate the effects of skid trails on soil ecological parameters for the manuscript ‘Severity of topsoil compaction controls the impact of skid trails on soil ecological processes’ by Klein-Raufhake et al 2024.

For Details, see the Method section of the related paper, published in Journal of Applied Ecology.