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Preprints
https://doi.org/10.5194/bg-2020-312
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-312
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  27 Aug 2020

27 Aug 2020

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A revised version of this preprint is currently under review for the journal BG.

Estimating immediate post-fire carbon fluxes using the eddy-covariance technique

Bruna R. F. Oliveira1, Carsten Schaller2, J. Jacob Keizer1, and Thomas Foken3 Bruna R. F. Oliveira et al.
  • 1Earth surface processes team, Center for Environmental and Marine Studies (CESAM), Department of Environment and Planning, University of Aveiro, Aveiro, Portugal
  • 2Climatology Research Group, Institute of Landscape Ecology, University of Münster, Münster, Germany
  • 3Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, Germany

Abstract. Wildfires typically affect multiple forest ecosystem services, with carbon sequestration being affected both directly, through the combustion of vegetation, litter and soil organic matter, and indirectly, through perturbation of the energy and matter balances. Post-fire carbon fluxes continue poorly studied at the ecosystem scale, especially during the initial window-of-disturbance when changes in environmental conditions can be very pronounced due to the deposition and subsequent mobilization of a wildfire ash layer and the recovery of the vegetation. Therefore, an eddy-covariance system was installed in a burnt area as soon as possible after a wildfire that had occurred on 13 August 2017, and has been operating from the 43rd post-fire day onwards. The study site was specifically selected in a Mediterranean woodland area dominated by Maritime Pine stands with a low stature that had burnt at high severity.

The carbon fluxes recorded during the first post-fire hydrological year tended to be very low, so that a specific procedure for the analysis and, in particular, gap filling of the eddy covariance data had to be developed. Still, the carbon fluxes varied noticeably during the first post-fire year, broadly revealing five consecutive periods. During the rainless period after the wildfire, fluxes were reduced but, somewhat surprisingly, indicated a net assimilation. With the onset of the autumn rainfall, fluxes increased and corresponded to a net emission, while they became insignificant with the start of the winter. From the mid winter onwards, net fluxes became negative, indicating a weak carbon update during spring followed by a strong uptake during summer. Over the first post-fire year as a whole, the cumulative net ecosystem exchange was −347 g C m−2, revealing a relatively fast recovery of the carbon sink function of the ecosystem. This recovery was mainly due to understory species, both resprouter and seeder species, since pine recruitment was reduced.

Specific periods during the first post-fire year were analyzed in detail for improving process understanding. Perhaps most surprisingly, dew formation and, more specifically, its subsequent evaporation was found to play a role in carbon emissions during the rainless period immediately after fire, involving a mechanism distinct from de-gassing of the ash/soil pores by infiltrating water. The use of a special wavelet technique was fundamental for this inference.

Bruna R. F. Oliveira et al.

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Bruna R. F. Oliveira et al.

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Daily Carbon Dioxide fluxes measured by an eddy-covariance station in a recently burnt Mediterranean pine stand in Central Portugal Oliveira, B. R. F., Keizer, J. J., and Foken, T. https://doi.pangaea.de/10.1594/PANGAEA.921281

Bruna R. F. Oliveira et al.

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Short summary
Forest fires have a significant impact on carbon dioxide emissions. The present study from pine forest in Portugal is one of the few where measurements of CO2 fluxes were started immediately (one and a half months) after the forest fire. Carbon dioxide emissions were linked to soil humidiy. Therefore, they started after the beginning of the rainfall in autumn. Due to the beginning of vegetation, the site was already a carbon dioxide sink the following year.
Forest fires have a significant impact on carbon dioxide emissions. The present study from pine...
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