Variation in soil organic carbon and nitrogen stocks and forest floor litter of natural and plantation black pine stands in Kastamonu

The impacts of stand development stages (SDS) and forest establishment types (FET) on litter amounts, as well as on soil organic carbon (SOC) and total nitrogen (TN) stocks, were investigated in black pine (Pinus nigra Arnold.) forests in Kastamonu. The litter amounts were determined by selecting eight experimental plots: four from natural black pine forests (NBP) and four from black pine plantations (PBP). A total of 24 litter samples were collected from each plot and arranged into three layers (L, F, and H) at the organic horizon. A total of 144 soil samples were collected and analysed for bulk density, SOC, and TN stocks. The results show that the PBP stands accumulated more litter (28.95 Mg ha⁻¹) than the NBP stands (21.4 Mg ha⁻¹). The highest value was found in stage "b" of the PBP stands at 29.59 Mg ha⁻¹, followed by stage "a" of PBP stands at 28.31 Mg ha⁻¹, stage "b" of NBP stands at 22.84 Mg ha⁻¹ and stage "a" of NBP stands at the lowest value of 19.95 Mg ha⁻¹. SOC and TN stocks in NBP stands (140.6 Mg C ha⁻¹ and 4.51 Mg N ha⁻¹) were generally higher than in the PBP stands (105.1 Mg C ha⁻¹ and 4.38 Mg N ha⁻¹), with more SOC and TN being accumulated in the soils of young stands. In this study on black pine forests, it is recommended that natural forests with high SOC and TN stocks be prioritized for conservation to increase carbon storage capacity, while silvicultural interventions (such as appropriate thinning and light management) be planned in plantation areas to accelerate the incorporation of accumulated dense litter into mineral soil. Also, given the decisive impact of stand development stages and soil depth on carbon dynamics, the adoption of site-specific, age-based management strategies in forest management plans is critical for the sustainability of the region's ecosystem.