Changes in organic carbon stocks in soils under Scots pine (Pinus sylvestris L.) stands in northern Poland over 26 years

Long-term changes in soil organic carbon (SOC) are relevant to the carbon cycle and global warming in coming decades. The possibility of the increasing of carbon sequestration in forest soils is disputable as climate warming can accelerate carbon fl uxes which affects the carbon stocks. Our study aimed at evaluating SOC stocks and its vertical distribution in forest soils over 26 years. Soils were sampled from genetic horizons in mature pine forest in northern Poland. The study was carried out on the same plots in 1992, 2008 and 2018. Organic carbon, total nitrogen and bulk density were determined at genetic soil horizons. SOC stocks were calculated in the 0–40 cm and 0–100 cm soil layers. The SOC stored to the depth of 40 cm was found to decrease by ca. 15% over 26 years. The SOC stocks decreased by 5% in 0–40 cm layer and by 9% in 0–100 cm layer over the last ten years. About 84–88% of the total SOC stocks was found in the 0–40 cm, out of which 40% was accumulated in the organic horizon. The results obtained indicate that no increase in SOC stocks in forest soils developed from sands may be expected over the next years, even though forests and forest soils represent a large reservoir of organic carbon. Keywords