|Biomass burning (fire) is used as a tool to aid in a number of land use and related changes, including: the clearing of forests and savannas for agricultural and grazing use; shifting agricultural practices; the control of grass, weeds, litter - and sometimes pests - on agricultural and grazing lands; the elimination of stubble and waste on agricultural lands after the harvest; and domestic use.||
The major components of biomass burning are forests (tropical, temperate,
and boreal); savannas; agricultural lands after the harvest; and wood for
cooking, heating, and the production of charcoal (Box 1). The burning
of tropical savannas is estimated to destroy three times as much dry matter
per year as the burning of tropical forests. The vast majority of the world's
burning is human-initiated, with lightning-induced natural fires accounting
for only a small percentage of the total.
Types of Biomass Burned:
Global estimates of annual amounts of biomass burning and of the resulting release of carbon into the atmosphere
|Source of Burning||Biomass burned
(Tg dry matter/yr)
(Tg dry matter/yr)
|Proportion of Total Carbon released (%)|
Agricultural wastes 2020 910 23.1
Tropical forests 1260 570 14.5
Fuelwood 1430 640 16.2
Temperate & boreal forests 280 130 3.3
Charcoal 21 30 1.0
|World Total 8700 3940 100.|
|Source: Adapted from Andreae (1991) in Environmental Science and Technology (1995).|
Pressures result from two main impacts of burning:
If the burned vegetation does not regenerate, the released carbon dioxide remains in the atmosphere. If the burned ecosystem completely regenerates, as the savannas tend to do under the right conditions, the carbon dioxide is eventually removed from the atmosphere via photosynthesis and is incorporated back into new vegetative growth. However, if regeneration is prevented - e.g. by excessive grazing / browsing of growing material, carbon dioxide is not re-incorporated within vegetation and/or the soil. Other gaseous emissions, however, remain in the atmosphere.
The gases produced are environmentally significant. The greenhouse gases
Carbon dioxide and Methane influence global climate. Combustion particulates
affect the global radiation budget and climate. Carbon monoxide, methane,
non-methane hydrocarbons, and nitric oxide are all chemically active gases
contributing to global warming or climate change.
Methyl chloride is a source of atmospheric chlorine, leading to the chemical
destruction of stratospheric ozone. Recently it was discovered that biomass
burning is also an important global source of atmospheric bromine in the
form of methyl bromine. Bromine leads to the chemical destruction of ozone
in the stratosphere and is about 40 times more efficient in that process
than is chlorine on a molecule-for-molecule basis.
Measurements have shown that in addition to the instantaneous production of trace gases and particulates resulting from the combustion of biomass matter, burning also enhances the biogenic emissions of nitric oxide and nitrous oxide from soil. It is believed that these emissions are related to increased concentrations of ammonium found in soil following burning. Ammonium, a major nitrogen component of the burn ash, is the substrate in nitrification, which is the microbial process believed responsible for the production of nitric oxide and nitrous oxide. The enhanced biogenic soil emissions of nitric oxide and nitrous oxide may be comparable to or even surpass the instantaneous production of these gases during biomass burning.
Changes in the levels of biodiversity can be illustrated
by examples where fire has been used under experimental conditions (see
2). In general, continued burning over a number of years results in
a long-term reduction in levels of biodiversity. However, some vegetation
communities are dependant on fire for their survival. Important considerations
are the frequency of fires (e.g. do they occur every year?) and the state
of the vegetation - how dry is it? This latter question is related to the
temperature at which the fires burn. Fires that burn late in a dry season
are hotter and more destructive than fires that occur earlier when the
vegetation still has residual moisture.
Impact of Bushfires on Floristic Diversity of Woodland in Côte d'Ivoire
Long-term research has been conducted on the impact of bushfires on floristic diversity of woodland. The effect of bushfire on the natural arboreal vegetation evolution was first studied in 1936 in Kokondekro by A. Aubreville on 7-year-old fallow land that held homogenous vegetation. The experimental field was divided into three plots of 2 hectares each. The first was protected against fire, the second was burnt annually on 15 December (early burning), whilst the third plot was burned on 15 March each year (late burning). Seven surveys completed between 1937 and 1994 indicate the evolution of the natural vegetation.
By combining estimates for the global annual amounts of biomass burning with information on the emission ratios for various compounds produced during burning, estimates of global emissions have been made (Box 3)
State indicators are therefore characterised by:
The results of burning are increased levels of atmospheric Carbon dioxide
and other emissions related to global warming.
The contribution of burning to global emissions. Comparison of global emissions from biomass burning with emissions from all sources, including biomass burning.
|Biomass burning(Tg element/yr)
|All sources (Tg element/yr)
|Biomass burning as of total (%)
The majority of fires in savannas and other grazing areas are anthropogenic in nature. As a result, changes to land use management practices can make significant differences to the important indicators listed above.
Response may therefore be characterised by:
Andreae, M.O. (1991). In Global Biomass Burning: Atmospheric Climatic and Biospheric Implications; Levine, J.S. E.; The MIT Press, Cambridge, MA.
NASA, 1999. Biomass burning and global change. http://asd-www.larc.nasa.gov/biomass_burn/biomass_burn.html
Levine, J.S. 1994. Biomass burning and the production of greenhosue gases. In: Zepp, R.G. (ed) 1994. Climate Biosphere Interaction: Biogenic Emissions and Environmental Effects of Climate Change. John Wiley and Sons. ISBN 0-471-58943-3. http://asd-www.larc.nasa.gov/biomass_burn/biomass.html
Environmental Science and Technology (1995). Biomass Burning: A Driver for Global Change. http://asd-www.larc.nasa.gov/biomass_burn/globe_impact.html
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