Precipitation-fire-functional interactions control biomass stocks and carbon exchanges across the world's largest savanna

Williams Mathew, Milodowski David T., Smallman T. Luke, Dexter Kyle G., Hegerl Gabi C., McNicol Iain M., O’Sullivan Michael, Roesch Carla M., Ryan Casey M., Sitch Stephen, Valade Aude. 2024. Precipitation-fire-functional interactions control biomass stocks and carbon exchanges across the world's largest savanna. Biogeosciences, 25 (6) : 1597-1614.

Url - jeu de données - Entrepôt autre : https://doi.org/10.7488/ds/7776

Résumé : Southern African woodlands (SAW) are the world's largest savanna, covering ∼ 3 M km2, but their carbon balance and its interactions with climate and disturbance are poorly understood. Here we address three issues that hinder regional efforts to address international climate agreements: producing a state-of-the-art C budget of the SAW region; diagnosing C cycle functional variation and interactions with climate and fire across SAW; and evaluating SAW C cycle representation in land surface models (LSMs). Using 1506 independent 0.5° pixel model calibrations, each constrained with local Earth observation time series of woody carbon stocks (Cwood) and leaf area, we produce a regional SAW C analysis (2006–2017). The regional net biome production is neutral, i.e. −0.08 Mg C ha−1 yr−1 (95 % uncertainty interval −1.67/1.66), with fire emissions contributing ∼ 0.88 Mg C ha−1 yr−1 (95 % uncertainty interval 0.36–2.51). Fire-related mortality driving fluxes from the total Cwood to dead organic matter likely exceeds both fire-related emissions from Cwood into the atmosphere and non-fire Cwood mortality. The emergent spatial variation in biogenic fluxes and C pools is strongly correlated with mean annual precipitation and burned area. However, there are multiple, potentially confounding, causal pathways through which variation in environmental drivers impacts the spatial distribution of C stocks and fluxes, which is mediated by spatial variations in functional parameters like allocation, wood lifespan, and fire resilience. More Cwood in wetter areas is caused by positive precipitation effects on net primary production and on parameters for wood lifespan but is damped by a negative effect with rising precipitation increasing fire-related mortality. Compared to this analysis, LSMs showed marked differences in spatial distributions and magnitudes of C stocks and fire emissions. The current generation of LSMs represents savanna as a single plant functional type, missing important spatial functional variations identified here. Patterns of biomass and C cycling across the region are the outcome of climate controls on production and vegetation–fire interactions which determine residence times, which is linked to spatial variations in key ecosystem functional characteristics.

Mots-clés Agrovoc : cycle du carbone, biomasse, distribution spatiale, sciage, accord international, émission atmosphérique, modèle de simulation, théorie Bayésienne

Mots-clés libres : Savanna, Climate, Precipitation, Fire, Carbon

Agences de financement hors UE : Natural Environment Research Council, National Centre for Earth Observation

Auteurs et affiliations

• Williams Mathew, University of Edinburgh (GBR) - auteur correspondant
• Milodowski David T., University of Edinburgh (GBR)
• Smallman T. Luke, University of Edinburgh (GBR)
• Dexter Kyle G., University of Edinburgh (GBR)
• Hegerl Gabi C., University of Edinburgh (GBR)
• McNicol Iain M., University of Edinburgh (GBR)
• O’Sullivan Michael, University of Exeter (GBR)
• Roesch Carla M., University of Edinburgh (GBR)
• Ryan Casey M., University of Edinburgh (GBR)
• Sitch Stephen, University of Exeter (GBR)
• Valade Aude, CIRAD-PERSYST-UMR Eco&Sols (FRA)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/611694/)

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