Timber harvesting shows persistent effects on soil hydrology and surface runoff 20 years past trafficking

Timber harvesting operations significantly impact soil hydrological parameters, particularly when heavy machinery is involved.

We quantified the recovery of skid trails by measuring soil physical properties and surface runoff one (H01) and three (H03) years after trafficking, and on a trail trafficked ca. 21 years prior (H21). Adjacent untrafficked plots served as controls to establish a baseline. The study site is a moderately sloped (18–26%) Stagnic Cambisol in the Flysch zone of the Vienna Woods. Soil properties were measured using undisturbed cores (250 cm³, n=3 per treatment and depth) at 5 and 15 cm depths. Surface runoff was assessed with high-intensity rainfall simulation experiments (100 mm h^-1, 50 m² plots).

Bulk density in control plots was low at both depths (5 cm: 0.96±0.07 g cm^-3; 15 cm: 1.00±0.12 g cm^-3). Trafficking increased bulk density at 15 cm by approximately 25%, with only partial recovery after 20 years, whereas at 5 cm it recovered to control levels (H21: 1.00±0.03 g cm^-3). Saturated hydraulic conductivity showed a similar trend, albeit with high variability. Water retention curves indicated a marked loss of macroporosity one and three years after trafficking at both depths. After 20 years, recovery was evident mostly in the topsoil. This produced a porous, recovered surface layer sitting on top a compacted hardpan at 15 cm depth.

Runoff dynamics reflected this stratification: H01 and H03 exhibited infiltration-excess overland flow with final surface runoff coefficients (Ψ_f) of 0.66 and 0.60 respectively, whereas H21 shifted to saturation-excess overland flow once the top layer was saturated (Ψ_f = 0.23).

These results demonstrate the long-term effect of subsurface compaction on clayey forest soils, underscoring the need to minimize trafficked area and to confine operations to permanently marked skid trails to safeguard soil functions and associated ecosystem services.