EGU2020-22260, updated on 16 Mar 2021
https://doi.org/10.5194/egusphere-egu2020-22260
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Spatial variability of the net ecosystem production and its component fluxes across a managed boreal forest landscape in Sweden: A biometric and chamber data-based analysis

Eduardo Martínez García1, Mats B. Nilson1, Hjalmar Laudon1, Jörgen Wallerman2, Johan E.S. Fransson2, Tomas Lundmark1, and Matthias Peichl1
Eduardo Martínez García et al.
  • 1Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), Umeå, Sweden
  • 2Department of Forest Resource Management, Swedish University of Agricultural Sciences (SLU), Umeå, Sweden

A managed boreal forest landscape is a diverse successional mosaic of clear-cuts to old-growth stands of different species growing on a variety of soil types. Consequently, this high spatial heterogeneity strongly impacts the forest net ecosystem production (NEP) across the managed landscape. However, the quantification of the variability of NEP and its component fluxes across forested landscapes is currently highly uncertain due to the complex interactions between forest structure and physiological processes and their changes over time.

Here, we assessed the spatial variability of NEP and its component fluxes during a 3-year period (2016-2018) over a boreal forest landscape (ca. 68 km2) located within the Krycklan catchment (64°14′N, 19°46′E) in northern Sweden. For this purpose, we selected 50 representative forest plots (10 m radius) across the catchment spanning various tree species (pine- and spruce-dominated stands) and forest age classes (from clear-cuts to old-growth forests). In each plot, forest floor CO2 fluxes were manually measured with custom-made closed chambers in monthly intervals during the growing seasons 2016-2018. Measurements were carried out across natural (both light/dark measurements) and trenching/vegetation removal plots (0.45 × 0.45 m) to partition the net forest-floor exchange (NEFF) into its contributing components, i.e., gross primary production (GPPFF) and respiration (ERFF). ERFF was further separated into plant autotrophic and soil heterotrophic respiration (RaFF and RhFF). Plot-level biometric measurements were conducted to determine the net primary production of trees and forest floor vegetation (NPPT and NPPFF) as well as heterotrophic dead wood respiration (decomposition, RhDW). Finally, NEP was calculated as NEP = NPPT + NPPFF – RhFF – RhDW.

Our results showed that NPPT consistently increased with forest ageing, while an opposite pattern was observed for NPPFF. In general, spruce stands showed lower NPPT compared to spruce stands at each given age class. In contrast, pine stands showed consistently higher NEFF, GPPFF, ERFF, RhFF, RaFF, and NPPFF compared to spruce stands. The forest floor was a net CO2 source, which increased with stand age due to the progressive decrease in GPPFF, while the ERFF remained similar among all the age classes. In addition, an analogous age-related pattern was observed in RhFF. Our findings also depicted an increasing NEP with forest age from about ≈ 54±67 g C m-2 yr-1 during the initial stages of development (i.e., 5-30 years-old) to a maximum of ≈ 170±68 g C m-2 yr-1 in middle-aged stands (i.e., 60-100 years-old). Higher NEP was generally observed for pine compared to spruce stands. Interestingly, we found that the old-growth forests steadily continue to accumulate C, which is contrary to the common view that they become C neutral or sources.

Overall, this comprehensive study improves our understanding of the spatial variability of the C balance over the heterogeneous regional forest landscape in northern Sweden, identifying tree species, forest floor vegetation and forest ageing as key drivers.

How to cite: Martínez García, E., Nilson, M. B., Laudon, H., Wallerman, J., Fransson, J. E. S., Lundmark, T., and Peichl, M.: Spatial variability of the net ecosystem production and its component fluxes across a managed boreal forest landscape in Sweden: A biometric and chamber data-based analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22260, https://doi.org/10.5194/egusphere-egu2020-22260, 2020.

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