Effects of red oak (Quercus rubra L.) and Scots pine (Pinus sylvestris L.) on early soil development during afforestation of nutrient-poor post-mining sands

The article aims to raise the knowledge on how the Northern red oak affects the soil formation and nutrient cycling compared to Scots pine during the early-stage reclamation of nutrient-poor mineral soil that originated in the deep soil layers in a former sand quarry. Furthermore, the aim is to also answer the question if the admixture of red oak helps to regenerate the soil properties more effectively than pure stands. Three treatments were established: pure red oak, pure pine, and a mixed stand, where organic [composite samples of L+F (litter and fermented), F+H (fermented and humic)] and mineral (A, C) soil horizons were analysed. The oak significantly outperformed the pine in the soil amelioration, showing elevated pH, higher base saturation, and enriched concentrations of basic cations in the humus horizons. The lower litter accumulation under the oak reflected the enhanced decomposability of its litter. A pattern of reduced cation exchange capacity, but the elevated base saturation of the oak soils suggested the development of a nutrient-rich microenvironment with a diminished risk of aluminium toxicity. Phosphorus remained critically limiting. The mixed stand exhibited intermediate properties closer to the pine stand, with the synergistic effects currently limited. Our results support red oak as an effective reclamation species for infertile post-mining soils, though sustained amelioration requires a decades-long perspective and integrated forest management strategies.