Soil organic carbon in Italian forests and agroecosystems: Estimating current stock and future changes with a spatial modelling approach

The soil organic carbon (SOC) is the largest carbon pool in the terrestrial biosphere, second only to oceans, containing twice as much carbon as the atmosphere and three times that stored in global vegetation. Climate change (CC) is expected to impact this carbon pool. To date, large uncertainties still persist on the effects of CC on SOC stocks. In addition, a shortage of data related to regional SOC quantities of tree-covered areas and future changes under CC conditions is recognized. In this work, we used a spatial-explicit modelling approach to estimate the current SOC stock (at 2005) and future changes (at 2095) under CC conditions of the whole forest, tree crop, grassland, and pasture covered areas of Italy. A methodology was preliminarily implemented to obtain spatialized SOC estimates at a regional scale by using the CENTURY 5 model coupled with spatialized vegetation, soil, and climate data. We ran both moderate (RCP4.5) and extreme (RCP8.5) climatic scenarios, and used three Global Circulation Models for each one of the four ecosystems described above. The current SOC stock estimates range from 51.3 (orchards) to 129.5 Mg carbon ha−1 (coniferous forests) and we found an overall SOC stock in Italy ranging from 1320.1 to 1425.1 Tg. SOC projections under CC showed a moderate carbon loss suggesting that forest, grassland, and permanent crop soils could provide an important contribution to climate change mitigation.