Atte Kumpu, Mikko Peltoniemi, Martin Forsius, Annikki Mäkelä. (2025). Soil carbon and nitrogen in unmanaged forests in Southern and Eastern Finland. Silva Fennica vol. 59 no. 3 article id 24072. https://doi.org/10.14214/sf.24072

Keywords: Norway spruce; boreal forest; mineral soil layer; organic soil layer

Highlights: Unmanaged forest soils store more carbon and nitrogen than managed forest soils; In unmanaged forest soils the carbon and nitrogen storages remain stable over time.

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Soils have an essential role in ecosystem carbon balance. The soils of natural-like old unmanaged forests have been studied less than those of managed stands. In this study, we collected soil core samples and measured the soil carbon and nitrogen content of 27 old unmanaged forest soils in Southern and Eastern Finland. The results were compared against existing data from managed stands of similar site types. The data was also compared with earlier soil measurements from the same sites to look for any significant changes. The analysis resulted in an average of 2.58, 2.44 and 1.62 kg m^-2 of soil carbon and 0.087, 0.097 and 0.074 kg m^-2 of nitrogen in the organic layer, 0–10 cm of mineral soil layer and 10–20 cm of mineral soil layer, respectively. Carbon contents in the mineral soil layers were higher in unmanaged forests than in managed forests, but not in the organic-layer. Similarly for nitrogen, there was a significant difference between the unmanaged forests and the managed stands for both mineral soil layers, but not for the organic layer. There were no significant changes in soil carbon or nitrogen contents between the old and new measurements in the old unmanaged forests. The results align with the assumption that carbon and nitrogen content are higher in unmanaged forests than in managed forests due to their higher litter input on average, and more stable and cooler conditions. This means that old unmanaged forests have an important role as carbon storage and that the carbon storage is stable.

Kumpu, University of Helsinki, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland https://orcid.org/0000-0001-9547-1697 E-mail: atte.kumpu@helsinki.fi
Peltoniemi, Natural Resources Institute Finland (Luke); Bioeconomy and environment, Latokartanonkaari 9, FI-00790 Helsinki, Finland E-mail: mikko.peltoniemi@luke.fi
Forsius, Finnish Environment Institute (Syke), Nature solutions, Latokartanonkaari 11, FI-00790 Helsinki, Finland https://orcid.org/0000-0003-0125-5120 E-mail: martin.forsius@syke.fi
Mäkelä, University of Helsinki, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland https://orcid.org/0000-0001-9633-7350 E-mail: annikki.makela@helsinki.fi

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