Five-year inter-annual variation in the net landscape carbon balance of a managed boreal forest landscape in Sweden

The boreal biome exchanges large amounts of carbon (C) with the atmosphere and thus significantly affects the global climate. A managed boreal landscape typically consists of various sinks and sources of carbon dioxide (CO₂), methane (CH₄), and dissolved organic and inorganic carbon (DOC and DIC) across forests with different stand ages, mires, lakes, and streams. Due to the spatial heterogeneity, a full understanding of the landscape-scale C balance requires capturing all C fluxes. Here, we investigate the five-year interannual variability in the net landscape carbon balance (NLCB) by compiling terrestrial and aquatic fluxes of CO₂, CH₄, DOC, DIC, and harvested C obtained from 2016 to 2020. For that purpose, we applied tall-tower eddy covariance measurements, stream monitoring, and remote sensing of biomass stocks (i.e. harvested C via clearcutting) to estimate the landscape-scale C fluxes across the land-water-atmosphere continuum for an entire boreal catchment (~68 km²) in Sweden. Our results show that this managed boreal forest landscape was a net C sink during 2016-2020 (123 ± 63 g C m^-2 yr^-1) with the lowest and highest sink-strength occurring during a wet year 2017 (16 g C m^-2 yr^-1) and a drought year 2019 (182 g C m^-2 yr^-1), respectively. The net landscape-atmosphere CO₂exchange was the dominant component of NLCB, followed by the C export via harvest and streams. We further found that global radiation and vapor pressure deficit regulated the inter-annual variations of NLCB, whereas forest biomass and source area contribution of mires determined its spatial variability. Overall, our multi-year NLCB investigations provide a holistic understanding of the inter-annual variations in NLCB of managed boreal forest landscapes to better evaluate their potential for mitigating climate change.