Stable organic carbon pool rises in soil under chestnut (Castanea sativa Mill.) forest for timber production after 15 years since grafting onto satin-cut stumps

Forest soils represent an important terrestrial organic carbon sink and the management practices could affect this C pool. The purpose of the present study was to investigate the effect of a forest restoration on the quantity and quality of the soil organic C (SOC). Since the widespread distribution of European chestnut (Castanea sativa Mill.) trees in European temperate forests, a 15 years old chestnut forest for timber production was selected on Northern Apennine chain (Italy) which was established on a clear–cut old chestnut stand. The soil sampling was performed in November 2004 (t0, before grafting), 2008 (t1) and 2019 (t2) through the digging of minipits down to 10 – 30 cm. In each minipit the surface and subsurface horizons were sampled and analysed for the determination of the total organic C content (TOC), and the C of fulvic acids (FA–C), humic acids (HA–C), humin (humin–C) and non–humic substances. Then, the total organic C stock (OCstock), the humification index (HI) and the humification rate (HR) were calculated. From t0 to t2 the mean thickness of subsurface horizon increased likely due both to the tree roots development and to the increased canopy cover due to tree growth which probably reduced the soil erosion. Generally, both TOC content and OCstock did not change over time. The FA–C and HA–C concentrations, instead, more sensitive to the change of management practises, generally reduced over time. This trend was also confirmed by the decline of HR. The humin–C content increased indicating an accumulation of the most recalcitrant SOC pool over time. Hence, the restoration of chestnut stands in mountainous areas, beyond to be a valid economic practice, has beneficial effects on the soil capacity to storage stable C