Soil Organic Carbon Dynamics in European Forests over the Period 2009–2018

Forest soils represent the largest carbon reservoir in terrestrial ecosystems, yet decadal scale changes in soil organic carbon (SOC) across Europe remain insufficiently quantified. Here, we analyze harmonized topsoil data from 0 to 20 cm in the LUCAS Soil Surveys conducted between 2009 and 2018 to investigate spatial patterns, environmental controls, and national level changes in forest SOC across the European Union and the United Kingdom. Using spatiotemporal machine learning models, we estimate a net SOC increase of approximately 1.31 Pg C over the decade, accompanied by pronounced regional heterogeneity. Climatic factors, particularly the aridity index, mean annual temperature, and available water capacity, emerged as the dominant drivers of SOC distribution, while forest structure, topography, and land cover change provided additional contributions. France, Sweden, and Germany accounted for the largest shares of total SOC gains and associated CO₂ equivalent reductions. These results highlight forest soils as dynamic and spatially heterogeneous carbon sinks and underscore their importance for national carbon accounting and climate mitigation strategies.