Estimating fire intensity, severity and greenhouse gas emissions for a working savanna landscape in Mali, West Africa

Savanna ecosystems are the largest and most frequently burned areas on earth. Savanna fires contribute significantly to Greenhouse gas (GHG) emissions although their precise impacts depend on a variety of variables including fire intensity, severity and combustion efficiency, which are thought to impact gas amounts and emission factors (EFs). While it is increasingly recognized that savanna fires play an important role in the global carbon cycle, there are few accurate estimates of their emissions and none from West Africa, the continent's most active fire region. Most estimates of emissions contain high levels of uncertainty because they are based on broad and naïve generalizations of diverse landscapes that are burned by complex fire regimes. To improve estimates, this study used a novel approach grounded in the burning practices of people who set fires to working landscapes. To determine the factors that influence fire emissions of three key gases-- CO₂, CO and CH₄ --we studied over 100 experimental fires using two field-based methods to measure emissions at plot level. Vegetation, fire timing, and season (early, middle or late) were selected based on local burning practices. Data were collected for savanna type, grass type, biomass composition and amount consumed, scorch height, speed of fire front, fire type and ambient air conditions for two mesic savanna sites in Mali. We used statistical analysis to determine the key factors effecting the fire intensity, severity, modified combustion efficiency (MCE) and EFs. Results suggest that fire type and fuel load and composition are important determinants of key variables and that mid-season fires have distinct characteristics—specifically, higher MCE and lower intensity—than early or late season fires. The implications of traditional burning practices on the key factors and the potential for GHG mitigation are discussed.