FiresAcross the Llanos Widespread biomass burning in northern South America that began in late 2002has continued into the new year. This true-color ModerateResolution Imaging Spectroradiometer (MODIS) image from the Terrasatellite on 04 January 2003, shows active fire detections (red dots) inColumbia and Venezuela .
Source: NASA/ EO
Some Details on Venezuelan Fires:
Different types of savanna formations constitute a veryimportant ecosystem in Venezuela from both ecological and socio-economicperspectives. More than one fourth of the country (approximately 22 million ha)is covered by savannas, found in most geographical regions, but mainly in theLlanos of the central part of the country. The vegetation formations whichdefine these savannas can vary substantially: From the open savannas, with acontinuous grass cover, occasionally interrupted by trees and shrubs and no morethan four gramineous species to the woody savannas, characterized by thepresence of trees and shrubs that can cover up to 15 percent of the area.
Agricultural activities have been traditionally established on agreat extension of the savanna area, through a very high dynamic process of landuse change, which fluctuates according to the country’s economic situation andspecific agricultural policies. Some of the most important crops are grown onsavannas such as corn, rice and sorghum, among others, while extensive andintensive cattle raising represents the most significant economic activity ofthese areas.
Savanna burning during the dry season is a common agriculturalpractice in the country, mainly to eliminate weeds and pests and encouragegrowth of new grass for animal grazing through the promotion of nutrientcycling. This periodical burning of a great portion of the savanna areasreleases important non-CO2 trace gases: methane, carbon monoxide, nitrous oxide,and nitrogen oxides. Carbon dioxide, which is also emitted in large quantities,is not included in the greenhouse gas inventory because, as knowledged by theIPCC methodology, it is reabsorbed by the vegetation regrowth between theburning cycles. Consequently, in an annual basis, net carbon dioxide emissionsfrom savanna burning is considered to be zero.
The proportion of the savanna areas burned in Venezuela ishighly uncertain as there are not reliable national statistics that compile, ona regular basis, the frequency and extent of savanna burning. Consequently, asatellite imagery study (Landsat TM, 1:250,000 scale) was performed on abouthalf of the savanna area of the country in order to determine this fraction andprovide a more reliable knowledge of this process.
The dates of the selected satellite images were made to coincidewith a time period towards the end of the dry season (March and April), underthe assumption that such a time framework would ensure the inclusion of most ofthe burning which could have occurred within the covered area. In order tochoose representative years around 1990, in terms of climatic conditions, theaverage monthly precipitation of the study area for a ten year series wascarefully analyzed so that the dates of the selected images would not coincidewith any particularly dry or wet year that could bias the study’s results.
A total of five satellite images at 1:250,000 scale were chosen,covering about 25 percent of the national territory and close to 50 percent ofthe savanna area. The interpretation was done visually while the areacalculation of the different vegetation units and burned portions was performedthrough the implementation of a Geographical Information System. The resultsfrom the study show that approximately 13% of the savanna area was burned onaverage. However, the fractions burned by region vary widely: from less than 1%in the Nor-oriente Region to almost 50% in the Centro-occidente Region. Thecorresponding burned fractions, obtained from the study, were extrapolated tothe entire savanna area in each region in order to estimate the average burnedarea in the country. Based on this extrapolation, an average of 3.1 million haof savannas are annually burned in the country.
Aboveground biomass density data were gathered from differentlocal studies, ranging from 3.3 to 6.1 t/ha dry matter, and have also beenassigned to specific regions, based on their proximity and general ecologicalcharacteristics. Similar approach was used to extrapolate the values provided bythe same studies on dead and live biomass fractions. These local data were usedto determine the amount of carbon released by the burnings. Theseresults are very controversial as the proportion savanna burned annually in thecountry (13%) obtained from the study, appears to be very low, especially whencompared to the regional data provided by the IPCC methodology. According todifferent local studies, conducted mainly in Africa and some parts of tropicalAmerica, it has been determined that savannas are burned worldwide every one tofour years on average. Discussions with various Venezuelan scientists have alsoconfirmed that savannas are very likely burned in the country in a much higher,but still undetermined, proportion than the fraction reported by the study.
Source: Ministry of Environment and Renewable Resources,Ministry of Energy and Mines, Venezuela. 1995. Preliminary National GreebhouseGas Inventory: Venezuela. UNEP Project GF/4102-92-40, 52 p. + Literature andAnnexes.