Soil Carbon Sequestration Following Natural Vegetation Recovery on Abandoned European Lands: Review and Research Needs

Natural vegetation recovery of abandoned agricultural lands could play a significant role in combating climate change by enhancing carbon (C) sequestration over time in a passive and cost-effective manner. After agricultural land is abandoned, natural regeneration processes, such as the regrowth of tree cover and increased microbial activity, typically restore soil organic carbon (SOC) sinks, thereby capturing atmospheric carbon dioxide (CO2). However, understanding its contribution to CO2 removal, particularly, on a large, continental scale, remains limited. In this systematic review, we aimed to gather studies investigating soil C sequestration following the abandonment of agricultural activities across Europe. By conducting an integrative analysis of data from 36 studies focusing on natural vegetation recovery after agricultural abandonment, we assessed the relative changes in SOC over time in relation to various environmental factors. Our findings revealed that SOC dynamics are influenced by management, soil reference group, exposition (aspect), and forest type, with remarkable increases found in Mediterranean regions, certain soil groups (Regosols, Cambisols, Calcisols), cropland-converted broadleaf and mixed forests, and specific aspects (North, South, and South-West facing sites). However, the results were strongly influenced by the uneven geographical and altitudinal distribution of study sites, which varied in terms of previous land use management, significantly affecting sequestration models. Most studies concentrated on the Mediterranean region, with grassland data predominantly coming from higher elevations. As a result, we call attention to a pressing need for broader research across Europe and present results of a gap analysis of recently abandoned croplands, highlighting especially underrepresented regions such as Northern Spain, Central France, the United Kingdom, Germany, Poland, the Baltic states, Hungary, and the Balkans, where SOC dynamics remain poorly documented. These findings provide a roadmap for researchers and policymakers to prioritize future SOC monitoring and natural vegetation recovery initiatives to enhance soil C sequestration across Europe.