An increase in natural disturbances (windthrow, bark beetle, and fire) in mountain spruce forests throughout Central Europe can have a significant negative impact on forest ecosystem services especially carbon sequestration. Forest disturbances alter carbon fluxes by affecting the balance between carbon uptake through gross primary production (GPP) and loss via ecosystem respiration (Reco), determining whether an ecosystem acts as a carbon sink or source. Initially, disturbances typically shift ecosystems to carbon emission, with recovery leading to increased sequestration, depending on disturbance type and intensity. While climate change impacts on carbon sequestration are well studied, the role of post-disturbance forest management in regulating carbon fluxes remains less explored, despite the recognized importance of reforestation.

The study analyzes carbon fluxes in Tatra National Park (TANAP), a member of the international Long-Term Ecological Research (LTER) network. In 2004, a large area of forest was heavily disturbed by wind. And subsequently, by fire and bark beetle outbreaks. The study was realized on sites representing different disturbance agents, fire (FIR), bark beetle (IPS) as well as different post-disturbance management - traditional salvage logging (EXT), natural processes (NEX), and intact reference conditions (REF). Study sites, each covering 100 ha, were situated in areas with comparable windthrow impact, ecological conditions, and climate. They were located on south and southeast-facing slopes with inclinations up to 15° at an altitude of 1050–1100 m a.s.l. The sites featured a larch-spruce forest (Lariceto-Piceetum community) growing on shallow, rocky dystric/podzolic cambisols.

Carbon flux measurements were conducted using two methods during different periods. Chamber transparent custom-built Vaisala probe (Vaisala, CarboCap 343) for micro ecosystem scale and Li-6400XT (LI-COR, Lincoln, NE, USA) for leaf scale were used from 2010 to 2015. Since 2018, eddy covariance methods (EC, model 7500-DS) have been used at the ecosystem-wide scale.

Chamber gas-exchange measurements revealed that herbaceous species such as Calamagrostis villosa and Rubus idaeus exhibited photosynthetic rates up to 19 µmol CO₂ m^-2 s^-1, significantly exceeding those of tree seedlings like Picea abies (8–13 µmol CO₂ m^-2 s^-1). Chamber-based soil respiration measurements also indicated substantial variability across ecosystem types, with fluxes of 953 gC m^-2 y^-1 in mature spruce forests, 905 gC m^-2 y^-1 in unmanaged windthrow, 617 gC m^-2 y^-1 in burnt windthrow areas, and 596 gC m^-2 y^-1 in managed windthrow sites. Additionally, chamber-based net ecosystem exchange (NEE) data highlighted variations in carbon balance across land cover types, with burnt windthrow acting as the strongest carbon sink (-463 ± 178 gC m^-2 y^-1), followed by managed windthrow (-352 ± 81 gC m^-2 y^-1) and unmanaged windthrow (-341 ± 92 gC m^-2 y^-1), whereas bark beetle-infested stands remained a net carbon source (+495 ± 176 gC m^-2 y^-1).

EC data showed that gross primary production (GPP) in unmanaged stands was 25% higher than in managed stands due to increased vegetation diversity and greater leaf area index (LAI). The maximum GPP recorded by EC was 14 gC m^-2 y^-1 in unmanaged sites and 12 gC m^-2 y^-1 in managed sites. However, total ecosystem respiration (Reco) was 104% higher in unmanaged sites compared to managed sites, with annual Reco values of 846 gC m^-2 y^-1 in managed stands and 1725 gC m^-2 y^-1 in unmanaged stands. EC-based NEE values indicated that managed stands transitioned to a carbon sink by 2019, while unmanaged stands remained a carbon source until 2020 and only became a net sink by 2021. Annual NEE values were -206 ± 115 gC m^-2 y^-1 in unmanaged stands and -136 ± 84 gC m^-2 y^-1 in managed stands.

These findings indicate that managed sites sequestered carbon more efficiently in the short term, while unmanaged stands exhibited higher long-term assimilation potential due to increased vegetation diversity. The study highlights the trade-offs in post-disturbance forest management, where salvage logging accelerates carbon sequestration but may reduce future stand diversity and resilience.