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Preprints
https://doi.org/10.5194/egusphere-2023-1852
https://doi.org/10.5194/egusphere-2023-1852
28 Aug 2023
 | 28 Aug 2023

Forest-floor greenhouse gas fluxes in a subalpine spruce forest: Continuous multi-year measurements, drivers, and budgets

Luana Krebs, Susanne Burri, Iris Feigenwinter, Mana Gharun, Philip Meier, and Nina Buchmann

Abstract. Forest ecosystems play an important role in the global carbon (C) budget by sequestering a large fraction of anthropogenic carbon dioxide (CO2) emissions and by acting as important methane (CH4) sinks. The forest-floor greenhouse gas (GHG; CO2, CH4 and nitrous oxide N2O) flux, i.e., from soil and understory vegetation, is one of the major components to consider when determining the C budget of forests. Although winter fluxes are essential to determine the annual C budget, only very few studies have examined long-term, year-round forest-floor GHG fluxes. Thus, we aimed to i) quantify the seasonal and annual variations of forest-floor GHG fluxes; ii) evaluate their drivers, including the effects of snow cover, timing, and amount of snow melt, and iii) calculate annual budgets of forest-floor GHG fluxes for a subalpine spruce forest in Switzerland. We measured GHG fluxes year-round during four years with four automatic large chambers at the ICOS Class 1 Ecosystem station Davos (CH-Dav). We applied random forest models to investigate environmental drivers and to gap-fill the flux time series. Annual and seasonal forest-floor CO2 emissions responded most strongly to soil temperature and snow depth (2.34±0.20 kg CO2 m-2 yr-1). No response of forest-floor CO2 emissions to leaf area index or photosynthetic photon flux density was observed, suggesting a strong direct control of environmental factors and a weak or even lacking indirect control of canopy biology. Furthermore, the forest-floor was a consistent CH4 sink (-19.1±1.8 g CO2-eq m-2 yr-1), with annual fluxes driven mainly by snow depth. Fluxes during winter were less important for the CO2 budget (6.0–7.3 %), while they contributed substantially to the annual CH4 budget (14.4–18.4 %). N2O fluxes were very low, negligible for the forest-floor GHG budget at our site. In 2022, the warmest year on record with also below-average precipitation at the Davos site, we observed a substantial increase in forest-floor CO2 emissions compared to other years. The mean forest-floor GHG budget indicated emissions of 2317±200 g CO2-eq m-2 yr-1 (mean±standard deviation over four years), with CO2 fluxes dominating and CH4 offsetting a small proportion (0.8 %) of the GHG budget. Due to the relevance of snow cover, we recommend year-round measurements of GHG fluxes with high temporal resolution. In a future with increasing temperatures and less snow cover due to climate change, we expect increased forest-floor CO2 emissions even at this subalpine site, with negative effects on its carbon sink behaviour.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
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Journal article(s) based on this preprint

24 Apr 2024
Forest-floor respiration, N2O fluxes, and CH4 fluxes in a subalpine spruce forest: drivers and annual budgets
Luana Krebs, Susanne Burri, Iris Feigenwinter, Mana Gharun, Philip Meier, and Nina Buchmann
Biogeosciences, 21, 2005–2028, https://doi.org/10.5194/bg-21-2005-2024,https://doi.org/10.5194/bg-21-2005-2024, 2024
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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This study explored year-round forest-floor greenhouse gas (GHG) fluxes in a Swiss spruce...
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