In many Mediterranean regions, wildfire regimes have intensified over the past decades, strongly reflecting human activities directly or indirectly. In Portugal, wildfires have been affecting, on average, 100.000 ha per year and over 300.000 ha in extreme years. A key societal concern regarding wildfires is its impacts on forest ecosystem services and, in particular, carbon sequestration. Forest policy and management have increasingly targeted the carbon sink potential of forest to offset greenhouse gas emissions. Wildfire affects forest carbon pools both directly, through combustion/heating processes, and indirectly, by changing abiotic (eg soil temperature) and biotic (eg leaf area index) conditions. These indirect impacts appear to be important, as model results have suggested that post-fire carbon losses are roughly equivalent to emissions during the fire. Furthermore, forest stands haven been found to act as carbon sink for 10 and more years after wildfire. Wildfire effects on forest carbon dynamics have mainly been addressed through biometric surveys of (annual changes in) carbon stocks. Studies measuring soil respiration effluxes have been less frequent and studies measuring eddy covariance fluxes even less. The well-established advantages of eddy covariance studies (field scale assessments over sub-hourly to annual periods) are offset by the equipment’s elevated costs and, possibly, by its stringent prerequisites in terms of site location, maintenance activities and data pre-processing. The combination of the 3 methodologies - as proposed here – has been advocated for refining process-based models used to assess larger scale effects on the carbon cycle. Only 1 of the previous eddy covariance studies seems to have addressed immediate post-fire conditions and then only for a short period (9 days), in spite post-fire carbon losses are expectedly at their maximum during the initial stages of the window-ofdisturbance. Furthermore, only 1 fire-related edd y covariance study appears to have been carried out in Europe, focussing on the effects of salvage logging 4 years after fire.

The overarching aim is to address the current knowledge gap on forest carbon fluxes and budgets immediately after wildfire, by combining 4 complementary methodologies and adding 2 novel components compared to prior studies (plant-level photosynthesis and carbon exports by overland flow). Based on the literature review and the team’s prior work in recently burnt areas (in eg FIRECNUTS and CASCDE), 6 hypotheses have been defined to guide the proposed research activities. In a nutshell, they address the 3 following topics: (i) direct and indirect effects of two contrasting fire severities (low vs. high) on vegetation, ash, litter and soil carbon pools; (ii) indirect effects of fire severity on carbon exports by overland flow and instantaneous rates of soil respiration and photosynthesis, and their evolution with time-since-fire; (iii) evolution, at the high-severity burnt site (worst-case scenario), of net ecosystem exchange and total ecosystem respiration with time-since-fire and its link with the temporal patterns in point-scale soil effluxes and net carbon assimilation rates.

CESAM members on this project

Ana Catarina Bastos
Researcher

Research Fellow

Bruna R F Oliveira
Research Fellow

Casimiro Pio
Researcher

Dalila do Rosário Encarnação Serpa
Researcher

Diana Catarina Simões Vieira
Researcher

Frank G.A. Verheijen
Researcher

Glória Catarina Cintra da Costa Pinto
Researcher

Isabel Maria Alves Natividade Campos
Research Fellow

João Puga
Researcher

Mário M. A. Cerqueira
Researcher

Nelson J. Cabaços Abrantes
Researcher

Oscar Gonzalez Pelayo
Researcher

Valdemar Esteves
Researcher