C. Hély

Emissions of major gaseous and particulate species during experimental burns of southern African biomass

Received 2 June 2005; revised 31 October 2005; accepted 23 November 2005; published 22 February 2006. [1] Characteristic vegetation and biofuels in major ecosystems of southern Africa were sampled during summer and autumn 2000 and burned under semicontrolled conditions. Elemental compositions of fuels and ash and emissions of CO2, CO, CH3COOH, HCOOH, NOX ,N H3, HONO, HNO3, HCl, total volatile inorganic Cl and Br, SO2 and particulate C, N, and major ions were measured. Modified combustion efficiencies (MCEs, median = 0.94) were similar to those of ambient fires. Elemental emissions factors (EFel) for CH3COOH were inversely correlated with MCEs; EFels for heading and mixed grass fires were higher than those for backing fires of comparable MCEs. NOX ,N H3, HONO, and particulate N accounted for a median of 22% of emitted N; HNO3 emissions were insignificant. Grass fires with the highest EFels for NH3 corresponded to MCEs in the range of 0.93; grass fires with higher and low MCEs exhibited lower EFels. NH3 emissions for most fuels were poorly correlated with fuel N. Most Cl and Br in fuel was emitted during combustion (median for each = 73%). Inorganic gases and particulate ions accounted for medians of 53% and 30% of emitted Cl and Br, respectively. About half of volatile inorganic Cl was HCl indicating significant emissions of other gaseous inorganic Cl species. Most fuel S (median = 76%) was emitted during combustion; SO2 and particulate SO4� accounted for about half the flux. Mobilization of P by fire (median emission = 82%) implies large nutrient losses from burned regions and potentially important exogenous sources of fertilization for downwind ecosystems.

Regional fuel load for two climatically contrasting years in southern Africa

[1] Available fuel loads for burning in savanna ecosystems in the southern African region have been estimated using a new Fuel load-Net Primary Production model based on ecophysiological processes such as respiration and Potential Evapotranspiration. The model outputs 15-day standing available fuel load layers for an entire year (a total of 24 layers). Published data from the Southern African Fire-Atmosphere Research Initiative (SAFARI-92) project and from the Southern African Regional Science Initiative (SAFARI 2000) field campaigns were generally in agreement with the estimations. Consistently with previous studies, precipitation was recognized to be the major climatic driver for fuel production. As a consequence, even though there was a regional increase in precipitation in 1999–2000 as compared to the 1991–1992 periods, the temporal and spatial variability in precipitation at fine scales (site level) was important enough to restrict generalities over the entire region for fuel load production. Four areas of interest, Etosha National Park (Namibia), Mongu (Zambia), Kasama (Zambia), and Kruger National Park (South Africa), were selected to reconstruct an aridity gradient and analyze their fuel load variability over the two years. These areas presented contrasting fuel load distributions for the two very different studied periods with arid areas producing heavier fuel loads in 1999–2000, and the more humid areas producing heavier fuel loads in 1991–1992. The consequences of such fuel load variability and the use of such results are discussed. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 1615 Global Change: Biogeochemical processes (4805); 1640 Global Change: Remote sensing; 3354 Meteorology and Atmospheric Dynamics: Precipitation (1854); 9305 Information Related to Geographic Region: Africa; KEYWORDS: climate, precipitation, net primary production, Fire, NOVI, tree cover

Using MODIS to evaluate heterogeneity of biomass burning in southern African savannahs: a case study in Etosha

As part of SAFARI 2000, this study investigated fire severity associated with, and emissions released from, a wildfire that burned a total area of approximately 3200 km2 of semi‐arid savannahs in the region of Etosha National Park, Namibia. Percent tree cover derived from Moderate Resolution Imaging Spectroradiometer (MODIS) data was used to scale up from site‐level field measurements to landscape‐level emission fields. Empirical relationships relating fuel load and combustion completeness to tree cover were developed from field observations. These relationships were coupled to the remotely sensed data to determine the emissions released over the entire area burned. Emissions from this single fire event were estimated to be 1.4×1012 g of CO2, 52.4×109 g of CO, 1.5×109 g of CH4, 1.85×109 g of non‐methane hydrocarbons (NMHC), and 2.4×109 g of particles less than 2.5 µm (PM2.5). A Normalized Burned Index difference (NBI diff), representative of fire severity and modified for MODIS data was used to assess the heterogeneity of the burned areas, but no significant correlation was found between this NBI diff and combustion completeness (CC).

FIRE REGIMES IN DRYLAND LANDSCAPES

Dryland regions are climatically defined as having low annual precipitation and dry season periods that can span over several months and take place once or twice a year. Dryland ecosystems (e.g., grasslands, savannas, or dry forests) that experience recurrent fires often exhibit fire-adapted (or “pyrophytic”) vegetation (Trabaud 1981; Scholes 1997; van Wilgen and Scholes 1997; Mistry 1998; Roques et al. 2001; Nicholas et al. 2011; Blackhall et al. 2017; Linder et al. 2017). Fire affects ecosystem dynamics in terms of species selection, regeneration, structure, nutrient cycling, and mortality. While this chapter is devoted to fire regimes, we will also summarize ecological impacts and feedbacks of fire on the environment and in particular on plant communities. Other impacts, such as the effects of fires on soil moisture dynamics, infiltration, and runoff production, are discussed in Chap. 2, while the effects on soil nutrient cycling and soil gas emissions are briefly analyzed in Chaps. 11 and 13. Additional discussion on the role of fire dynamics on different biomes, e.g., grasslands, shrublands, dry forests, and savannas, can be found in Chaps. 16 and 17, while the effects of fire on land–atmosphere interactions are discussed more in detail in Chap. 7.