Forest management reduces soil carbon sequestration potential in European temperate forests

In recent years, the carbon (C) balance of temperate forests has been the focus of growing research interest, as even European temperate forests have shown potential to serve as effective CO2 sinks. However, almost all the attention has predominantly focused on the aboveground biomass of the trees, while C accumulated in forest soils has largely been neglected. This study provides a comparative quantitative assessment of total soil C stored in the forest soils subjected to varying degrees of human influence, highlighting their role in the overall carbon budget in the temperate forests of Central Europe. We found that soil C stocks in unmanaged forests, with likely low or no human influence in the past, generally exceed those in adjacent managed forests. However, some unmanaged forests, despite being protected for several decades, had lower soil C stocks than adjacent managed forests, likely due to severe historical human exploitation. Soil C stocks (down to 40 cm of mineral topsoil) in managed forests ranged from 1117 g/m2 to 2058 g/m2, while in unmanaged forests, they ranged from 774 g/m2 to 3490 g/m2. Among different soil horizons, fermentation and humification (FH), and 0-10 cm, 10-20 cm, and 20-40 cm of mineral soil, the upper mineral soil layer (0-10 cm) contributed most to C stocks (32 % to 47 %). In conclusion, forests that have remained unmanaged with little to no historical human impact tend to store significantly more soil C than recently managed forests. These findings highlight the significant role of unmanaged forests in soil carbon sequestration, underscoring the need to consider soil C in forest management strategies.