Clear-cut-based rotation forest management (RFM) is the dominant silvicultural system in boreal forests. Continuous-cover forestry (CCF), an emerging alternative, operates without clear-cutting. How these silvicultural regimes affect long-term SOC storage and quality remains unclear. This dataset contains measurements from a field study that examined the effects of CCF and RFM on SOC quantity and stabilization in spruce-dominated forests in central Finland. We sampled (1) recently clear-cut plots, (2) even-aged mature plots (both representing RFM stages), (3) uneven-aged CCF plots, and (4) uncut controls. We analysed SOC stocks, root biomass, condensed tannins (root metabolites) and soil fungal necromass (indicated by glucosamine). SOC recalcitrance and accessibility for decomposition were assessed through chemical and physical fractionation and laboratory incubation. 13C and 15N abundances indicated the decomposition stage of soil organic matter (SOM) and the contribution of mycorrhizal residues. Uncut forests had marginally higher root biomass than clear-cut and even-aged forests, while uneven-aged forests fell in between. Tannin concentrations were decreased in clear-cut plots. Fungal necromass correlated strongly with SOC but was unaffected by forest management. Contrastingly, greater 15N enrichment in CCF plots suggested higher impact of mycorrhizae in SOM formation. Although soil respiration rate in uncut plots was higher than in managed plots, chemical and physical fractionation analyses showed no treatment effects. While we did not find differences in total SOC stocks between treatments, our results revealed long-term management impacts on SOC quality and stabilization processes, as mycorrhizal fungi appeared to be more involved in SOM formation in uneven-aged plots. This may indicate a greater potential for long-term accumulation of stable SOM.

More clarification of terms and units can be found in the sheets named "metadata" in the data file.

More detailed method descriptions can be found in the publication linked to this dataset.

Soil characteristics

All soil attributes have been assessed separately for the organic topsoil layer (O-layer) and mineral soil (min), if not specified otherwise.

SOC stocks: calculated based on C content (of fine earth fraction), bulk density, and volume of soil layer

Root biomass: hand-picked, oven-dried (65 degrees C), sorted into tree fine roots (<2 mm), tree coarse roots (> 2 mm), dead roots, and understorey roots.

Condensed tannins: concentration of condensed tannins in the soil was analyzed with an acid-butanol assay.

Cumulative soil respiration under standardized conditions was measured during a 28 days laboratory incubation.

Soil fungal necromass: the amino sugar glucosamine was used as an indicator for fungal necromass.

Chemical fractionation: Conducted from organic layer samples, first nonpolar extractives with dichloromethane, followed by a hot water extraction to dissolve polar extractives and followed by acid hydrolysis with sulphuric acid. Chemical fractionation was conducted for O-layer samples and for the light particulate organic carbon (POM) fraction in the mineral soi.

Physical fractionation: Conducted for organic matter in mineral soil. We first separated based on size: particulate organic matter (POM) > 0.63 μm was separated from mineral associated organic matter (MAOM) < 0.63 μm by wet-sieving. Then we separated based on density with a Sodiumpolytungstate solution with a density of 1.85 g cm ^-3. Heavy POM sunk to the bottom, whereas light POM floated on top.

13C and 15N abundance: isotope concentrations were assessed for O-layer samples, POM and MAOM.

Soil temperature, surface temperature and soil moisture were assessed every 15 minutes throughout one year (Oct 2020-Sep 2021)

Forest stand characteristics

Mean diameter at breast height, basal area and dominant tree height of the tree stand were assessed in each plot.

Ground vegetation coverage was visually assessed for dwarf shrubs, herbs, grasses, mosses and lichen.