Variable carbon losses from recurrent fires in drained tropical peatlands

Tropical peatland fires play a significant role in the context of global warming through emissions of substantial amounts of greenhouse gases. However, the state of knowledge on carbon loss from these fires is still poorly developed with few studies reporting the associated mass of peat consumed. Furthermore, spatial and temporal variations in burn depth have not been previously quantified. This study presents the first spatially explicit investigation of fire-driven tropical peat loss and its variability. An extensive airborne LiDAR (Light Detection and Ranging) dataset was used to develop a pre-fire peat surface modeling methodology, enabling the spatially differentiated quantification of burned area depth over the entire burned area. We observe a strong interdependence between burned area depth, fire frequency and distance to drainage canals. For the first time, we show that relative burned area depth decreases over the first four fire events and is constant thereafter. Based on our results, we revise existing peat and carbon loss estimates for recurrent fires in drained tropical peatlands. We suggest values for the dry mass of peat fuel consumed that are 206 t ha(-1) for initial fires, reducing to 115 t ha(-1) for second, 69 t ha(-1) for third and 23 t ha(-1) for successive fires, which are 58% to 7% of the current IPCC Tier 1 default value for all fires. In our study area, this results in carbon losses of 114, 64, 38 and 13 t C ha(-1) for first to fourth fires, respectively. Furthermore, we show that with increasing proximity to drainage canals both burned area depth and the probability of recurrent fires increase and present equations explaining burned area depth as a function of distance to drainage canal. This improved knowledge enables a more accurate approach to emissions accounting and will support IPCC Tier 2 reporting of fire emissions. This article is protected by copyright. All rights reserved

An outlook on the Sub-Saharan Africa carbon balance

This study gives an outlook on the carbon balance of Sub-Saharan Africa (SSA) by presenting a summary of currently available results from the project CarboAfrica (namely net ecosystem productivity and emissions from fires, deforestation and forest degradation, by field and model estimates) supplemented by bibliographic data and compared with a new synthesis of the data from national communications to UNFCCC. According to these preliminary estimates the biogenic carbon balance of SSA varies from 0.16 Pg C y[Superscript: −1] to a much higher sink of 1.00 Pg C y[Superscript: −1] (depending on the source data). Models estimates would give an unrealistic sink of 3.23 Pg C y[Superscript: −1], confirming their current inadequacy when applied to Africa. The carbon uptake by forests and savannas (0.34 and 1.89 Pg C y[Superscript: −1], respectively,) are the main contributors to the resulting sink. Fires (0.72 Pg C y[Superscript: −1]) and deforestation (0.25 Pg C y[Superscript: −1]) are the main contributors to the SSA carbon emissions, while the agricultural sector and forest degradation contributes only with 0.12 and 0.08 Pg C y[Superscript: −1], respectively. Savannas play a major role in shaping the SSA carbon balance, due to their large extension, their fire regime, and their strong interannual NEP variability, but they are also a major uncertainty in the overall budget. Even if fossil fuel emissions from SSA are relative low, they can be crucial in defining the sign of the overall SSA carbon balance by reducing the natural sink potential, especially in the future. This paper shows that Africa plays a key role in the global carbon cycle system and probably could have a potential for carbon sequestration higher than expected, even if still highly uncertain. Further investigations are needed, particularly to better address the role of savannas and tropical forests and to improve biogeochemical models. The CarboAfrica network of carbon measurements could provide future unique data sets for better estimating the African carbon balance

The Sub-Saharan Africa carbon balance, an overview

This study presents a summary overview of the carbon balance of Sub-Saharan Africa (SSA) by synthesizing the available data from national communications to UNFCCC and first results from the project CarboAfrica (net ecosystem productivity and emis- sions from fires, deforestation and forest degradation, by field and model estimates). 5 According to these preliminary estimates the overall carbon balance of SSA varies from 0.43 Pg C y − 1 (using in situ measurements for savanna NEP) to a much higher sink of 2.53 Pg C y − 1 (using model estimates for savanna NEP). UNFCCC estimates lead to a moderate carbon sink of 0.58Pg C y − 1 . Excluding anthropogenic disturbance and intrinsic episodic events, the carbon uptake by forests (0.98 Pg C y − 1 ) and savannas 10 (from 1.38 to 3.48 Pg C y − 1 , depending on the used methodology) are the main com- ponents of the SSA sink e ff ect. Fires (0.72 Pg C y − 1 ), deforestation (0.25 Pg C y − 1 ) and forest degradation (0.77 Pg C y − 1 ) are the main contributors to the SSA carbon emis- sions, while the agricultural sector contributes only with 0.12 Pg C y − 1 . Notably, the impact of forest degradation is higher than that caused by deforestation, and the SSA 15 forest net carbon balance is close to equilibrium. Savannas play a major role in shap- ing the SSA carbon balance, due to their large areal extent, their fire regime, and their strong interannual NEP variability, but they are also a major uncertainty in the overall budget. This paper shows that Africa plays a key role in the global carbon cycle sys- tem and probably could have a potential for carbon sequestration higher than expected, 20 even if still highly uncertain. Further investigations are needed, particularly to better address the role of savannas and tropical forests. The current CarboAfrica network of carbon measurements could provide future unique data sets for better estimating the African carbon balance