Soil organic carbon stock changes in a Mediterranean mountain pasture characterized by transhumant sheep grazing

C storage in grasslands has been estimated to comprise between 10-30% of global soil C. More than half of the world's land surface is grazed, accounting for approximately one fourth of potential C sequestration in world soils. Due to this large potential, significant research efforts have been oriented toward characterizing this potential for C sequestration in grazed lands. Many scientific studies concur that grazing may have a positive effect on soil C concentrations at low and moderate grazing levels, and negative at high grazing levels. However, this has not been characterized fully for extensive Mediterranean high mountain pastures. A study of extensive grazing effects on soil C stocks was carried out in the Parque Natural Sierras de Cazorla, Segura, y Las Villas, specifically within an area of the park (Campos Hernán Perea) where grazing has persisted for centuries. In this area, the majority of sheep herds are transhumant, with grazing over the extensive area from May-November each year. Digital maps of grazing intensity based on GPS tracking collar data from both day and night movements were elaborated for the whole region, allowing a fine-scale estimation of grazing intensity. Paired samples were taken un non-encroached (grassland) and encroached (shrub-covered) soils in this landscape. Soil sampling was to 5 cm depth with metallic cylinders (Ekjelkamp) of 5 cm height and with a volume of 100 cm³, and soils were analyzed for organic C with elemental analysis following decarbonatization. SOC stock was found to be positively associated with both grazing and encroachment in a non-antagonistic manner. SOC stocks to 5 cm were estimated to be a minimum of 13.8 Mg ha^-1 with no grazing and encroachment, and 25.5 Mg ha^-1 with high grazing intensity and encroachment. The results highlight the very crucial influence of grazing and landscape vegetation dynamics for SOC stock estimates in grazed lands.