Withey, Kieran and Barlow, Jos and Espirito-Santo, Fernando (2019) Quantifying the immediate carbon emissions from El Niño-mediated wildfires in humid tropical forests. Masters thesis, Lancaster University.
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Abstract
Wildfires produce substantial CO2 emissions in the humid tropics during El Niñomediated extreme droughts, and these emissions are expected to increase in coming decades. Immediate carbon emissions from uncontrolled wildfires in human-modified tropical forests can be considerable owing to high necromass fuel loads. Yet, data on necromass combustion during wildfires are severely lacking. The present study evaluated necromass carbon stocks before and after the 2015– 2016 El Niño in Amazonian forests distributed along a gradient of prior human disturbance. Landsat-derived burn scars were used to extrapolate regional immediate wildfire CO2 emissions during the 2015–2016 El Niño. Before the El Niño, necromass stocks varied significantly with respect to prior disturbance and were largest in undisturbed primary forests (30.2 ± 2.1 Mg ha-1, mean ± s.e.) and smallest in secondary forests (15.6 ± 3.0 Mg ha-1). However, neither prior disturbance nor a proxy of fire intensity (median char height) explained necromass losses due to wildfires. In the 6.5 million hectare (6.5 Mha) study region, almost 1 Mha of primary (disturbed and undisturbed) and 20,000 ha of secondary forest burned during the 2015–2016 El Niño. Covering less than 0.2% of Brazilian Amazonia, these wildfires resulted in expected immediate CO2 emissions of approximately 30 Tg, three to four times greater than comparable estimates from global fire emissions databases. Uncontrolled understorey wildfires in humid tropical forests during extreme droughts are a large and poorly quantified source of CO2 emissions.