Exploring the role of shrubs in modulating heavy metal accumulation in forest soils in single-species pine stands

Heavy metals accumulate and bind strongly in soil, making them difficult to eliminate. The objective of this study was to evaluate the effect of alder buckthorn (Frangula alnus) and European hazelnut (Coryllus avellana) admixtures in pine monocultures on the accumulation and vertical distribution of heavy metals in soil surface horizons. Ten sites each of pine stands admixed with alder buckthorn, pine stands admixed with European hazelnut, and pine monocultures in the Rybnik Forest District in southern Poland were selected for each variant. For the study, soil samples were taken from each site from the organic and mineral horizons and analysed for N and C contents, C/N ratio, pHH2O, base cation contents, and heavy metal contents. For all three stand compositions, the organic horizons showed a significant accumulation of heavy metals compared to the mineral horizons. Heavy metal content was correlated with pH, N and C contents, C/N ratio, and base cation contents. The admixture of shrubs, especially European hazelnut, positively affected soil organic matter quality and, consequently, the accumulation of heavy metals. European hazelnut had the most beneficial soil effects on the tested soil, which confirms that this species can be used in planning species composition, particularly in regions prone to heavy pollutant deposition.