Macrofauna and Organic Matter in Postagrogenic Sandy Soils in the Northwest of Smolensk Oblast (Russia)

Natural reforestation on abandoned arable lands is one of the characteristic processes that trigger the transformation of soil organic matter accompanied by changes in the abundance, biomass, and taxonomic structure of soil macrofauna. The assessment of the time for a potential return of soil properties and macrofauna to their natural state, dynamics of soil organic matter stocks, and the role of macrofauna in this process at different stages of postagrogenic successions is relevant in the context of predicting the changes in ecosystem components and their role in organic carbon sequestration under various land use scenarios. The stock of organic carbon, soil morphological properties, as well as the abundance, biomass, and taxonomic structure of soil macrofauna in arable lands of five stages of pine forest restoration (fallow meadows and pine forests of different ages), and primary forests in the Smolenskoye Poozerye (Smolensk Lakeland) National Park (Smolensk oblast, Russia) have been examined. The soils of 85-100-year-old pine forests retain the lower boundary of the former humus horizon; at the meadow stage, restoration signs appear, namely, a shallow humus horizon pierced with roots and later transformed into a raw-humus horizon in young forests. By the age of 80, the carbon stock in the mineral soil part restores to almost background values. The soil macrofauna composition radically changes with the substitution of meadow communities by forest ones. At the initial stages (in agrocenoses and fallow meadows), the macrofauna of organomineral soil horizons is prevalent, being represented by soil earthworms and larvae of scarab beetles. Further, the macrofauna of organic horizons is restored to contain a high share of saprophages, such as epigeic and epi-endogeic earthworms, which contribute to the differentiation of litter into subhorizons. The biomass of saprophages negatively correlates with the carbon stock in the mineral part of forest soils, its content in the litter, and litter thickness and positively correlates with the share of easily decomposable litter fraction.

Automated summary

Natural reforestation on abandoned arable lands triggers changes in soil organic matter and the abundance, biomass, and taxonomic structure of soil macrofauna. Understanding the dynamics of soil properties, organic matter stocks, and the role of macrofauna in this process is crucial for predicting ecosystem changes and carbon sequestration. A study in Russia's Smolensk Lakeland National Park examined the carbon stocks, soil morphological properties, and macrofauna composition in different stages of pine forest restoration. The results showed that the composition of soil macrofauna changes with the substitution of meadow communities by forest ones, and the biomass of saprophages is negatively correlated with carbon stock in forest soils.