Post-agrogenic development of vegetation, soils, and carbon stocks under self-restoration in different climatic zones of European Russia

• Post-agrogenic self-restoration of soils of different climate was analyzed with chronosequential approach.
• Vegetation and soils developed towards their natural conditions.
• A recovery of SOC stocks was observed.
• Active and passive OC pools reflected an increase of total SOC.
• No full restoration was found within the time of 42–170 years.

The objective of this study was to provide a general concept of post-agrogenic self-restoration of vegetation, soils, and carbon stocks in different climatic zones of European Russia based on comparative analysis of our previous studies (Kalinina et al., 2009, 2010, 2011, 2013, 2014). The focus was on post-agrogenic plant succession, pedogenesis, carbon stocks and different carbon pools of Podzols and Albeluvisols of the taiga, Chernozems of the semi-humid steppe, and Calcisols–Solonetzes of the semi-arid steppe of Russia. During self-restoration, vegetation and soils developed towards their natural conditions. Former homogenous plow horizons developed a vertical stratification in terms of the morphological and chemical properties typical of the undisturbed soils, promoting pedodiversity. With the exception of the post-agrogenic Chernozems, the plow boundary was present during the studied period of self-restoration (42–170 years). The trend towards natural soils was also observed in every chronosequence in terms of increasing soil organic carbon (SOC) dynamics, indicating a net carbon sink function during self-restoration. Accelerated SOC gains occurred when forests established in the taiga and steppe species appeared in the Chernozem and Calcisol sequences. SOC gains occurred in the taiga mostly within the organic surface layer whereas in the steppe areas within the mineral topsoil of 0–0.2 m. The investigation of different carbon pools showed a significant organic carbon (OC) enrichment of the density fractions < 1.8 g cm− 3 (free particulate organic material (POM) and occluded POM) and the density fractions > 1.8 g cm− 3 (sand coarse/medium silt, fine silt, clay) following the increase of total SOC during self-restoration. In the taiga, SOC restoration time was almost identical with the duration of natural plant succession of about 150 years; in the steppe areas, SOC restoration took about 100 years and was longer than plant succession. Although self-restoration developed towards natural conditions, a full recovery was hardly ever reached, revealing that self-restoration is a long or infinitely long-term process.