Wild boar impact on soil properties in a grassy area: interactions of rooting, slope position and shrub encroachment

Abstract Background Wild boar ( Sus scrofa ) rooting can have diverse effects on soil properties, which could be much more complex to predict in the presence of shrub encroachment and varied microtopography. This study aimed to evaluate the interactive effects of wild boar rooting and shrub encroachment on soil properties in a sloping (2–6°), mildly eroded grassland in Budapest, Hungary. Soil samples were collected from both upper and lower slope positions at 0–5 cm and 5–10 cm depths across four distinct microsites: rooted patches, the redistributed soil surrounding the excavated depressions (“rings”), and two adjacent control patches (open grassy patches and areas beneath shrubs). Using a near-infrared spectrometer, we analyzed pH, total nitrogen (N), phosphorus (P), exchangeable potassium (K), exchangeable calcium (Ca), exchangeable magnesium (Mg), total iron (Fe) and clay content. Differences among microsites were evaluated using a Bayesian mixed effects regression model. Results Slope position significantly influenced N and P concentrations, with higher values observed at the lower slope than at the upper slope (1.7–2.0 vs. 1.3–1.7 g/kg for N in grassy patches and 28.8–33.2 vs. 22.1–27.7 mg/kg for P in shrub-encroached patches, respectively). Rooted patches exhibited reduced concentrations of N (1.08–1.31 g/kg), P (21.88–25.05 mg/kg) and K (3.70–4.17 mmol/kg), while Fe (23.8–25.0 g/kg) and clay (21.8–23.1%) were elevated. Although vegetation cover may influence nutrient distribution, a significant effect was confirmed only for Ca, which showed higher levels beneath shrubs than in grassy areas at the upper slope. The interaction between slope position and rooting was not a strong predictor in the model, suggesting limited impact of rooting on nutrient retention. Conclusions These findings demonstrate that wild boar rooting significantly alters soil chemical properties, primarily through soil mixing in deep rootings, but their impact may be overridden by slope position. In summary, our results suggest that slope and wild boar rooting influence soil nutrient distribution, but there is little evidence supporting a mitigating role of shrub encroachment or rooting on slope-related erosion impacts. Further conservation efforts in grasslands should consider the joint processes of those factors to prevent soil degradation.