CO2 and CO emission rates from three forest fire controlled experiments in Western Amazonia
Graphical abstract
Introduction
Amazon forest is one of the largest ecosystem carbon pools on Earth (Brienen et al., 2015). According to Feldpausch et al. (2012) this ecosystem stores around 150–200 Pg C of living biomass and soils. The Amazon forest represents a third of the world's tropical forests (Barber et al., 2014) and contains 13.0% of the world's biota (Lewinsohn and Prado, 2005).
Despite the importance of the Amazon forest, its burning, as part of the conversion of mature tropical forests to agriculture and pastures, has been common practice in the Amazon region, and contributes significantly to the release of gas and particulate atmospheric pollutants (Crutzen and Andreae, 1990). For Feldpausch et al. (2012) and Gatti et al. (2014), the Amazon rainforest can become a net source of atmospheric carbon and lose its function as a carbon sink, that as a result of the combined effects of drought and frequent fires.
The emissions are an effective source of several greenhouse gases such as CO2, CH4 and N2O, and other pollutants such as NOx, CO and volatile carbon compounds (Chen et al., 2010, Fearnside et al., 2009, Crutzen and Andreae, 1990). Emissions of CO and CH4 perturb the atmospheric oxidation efficiency by reaction with hydroxyl radicals (Alves et al., 2010). The main carbon product generated during biomass combustion is CO2. The highest proportion of CO2 is emitted during the flaming phase, while CH4, CO and other hydrocarbons are mainly emitted during the smoldering phase (Lobert et al., 1991, Ward and Hardy, 1991). The impact of these emissions on air pollution and global warming has been widely studied (Johnston et al., 2012, Bowman et al., 2009, Naeher et al., 2007).
CO2 emissions estimates due to land use change in tropical areas vary widely. Tropical forests, especially in the Amazon forest, contain a large quantity of biomass and are one of the last agricultural frontiers (Righi et al., 2009). Agriculturists use fire in the Amazon basin for establishing and maintaining farm and grazing land. It is estimated that, from 1850 to 1980, between 90 and 120 billion metric tons (90–120 trillion kilograms) of CO2 were released into the atmosphere from tropical forest fires (NASA, 2011). Comparatively, during that same time period, an estimated 165 billion metric tons of CO2 were added to the atmosphere by industrial nations through the burning of coal, oil, and gas. Today, an estimated 5.6 gigatons of carbon are released into the atmosphere each year due to fossil fuel burning. Burning of tropical forests contributes another 2.4 gigatons of carbon per year, which corresponds to about 30.0% of the total (NASA, 2011).
In Brazil, an average of 17,000 km2 yr−1 of primary forests is burned (Andreae and Merlet, 2001). The average deforestation rate of the legal Amazonian region was 13,684 km2 yr−1 during the 2000 to 2014 period (INPE, 2014).
Most recent developments on wildland fire emissions, carbon and climate include the discussions of Weise and Wright (2014) on characterization of fuels, Loehman et al. (2014) on carbon dynamics, Ottmar (2014) and van Leeuwen et al. (2014) on fuel consumption, and Urbanski (2014) on emission factors. However, large uncertainties still exist on carbon emissions from tropical deforestation fires due to the complex tree species composition, variety of ecosystem types, fuel loading, and fuel moisture, as described by Riggan et al. (2004).
The quantification of such emissions is essential to predict environmental impacts (Neto et al., 2009, Righi et al., 2009, Carvalho et al., 2001). Furthermore, the reduction of carbon emissions, resulting from burns, is an important strategy to reduce climate changes (Arima et al., 2014, Gonzalez et al., 2014).
In spite several studies on forest fires were conducted during the past two decades, there is still a need to better investigate the impact of this type of biomass burning on global and regional CO2 and CO emissions.
CO2 and CO emissions are estimated from carbon contained in the biomass above the ground. The quantification of carbon content can be made using forest inventory, which is a method of direct measurement (Gonzalez et al., 2014). For Asner and Mascaro (2014), a larger number of forest inventories must be done to make the mapping of tropical forest carbon widely available.
The main objective of this work was to estimate the amount of CO2 and CO emitted by the fires in the Western Amazonia. Biomass was quantified before and after the fire in the central 1-ha of area deforested and burned in three places of the Western Amazonia (Cruzeiro do Sul, Rio Branco and Candeias do Jamari). A special effort was put into determining biomass consumption of logs, in which the largest part of the biomass is concentrated. This research is part of a project to quantify the main emission and consumption parameters of Amazonia forest fires. Most recent research within the project includes CO2, CO, CH4 and particulate matter emission from biomass combustion (Amaral et al., 2014, Amorim et al., 2013, Costa et al., 2012, Neto et al., 2011), and forest regeneration (d'Oliveira et al., 2011).
Section snippets
Test site
The values obtained for Western Amazonia were calculated from field tests conducted in Cruzeiro do Sul, Rio Branco and Candeias do Jamari. Experimental repetitions were not performed in these three locations.
Fig. 1 shows the location of the test sites, nearby the cities of Cruzeiro do Sul and Rio Branco, in state of Acre, and Candeias do Jamari, in state of Rondônia. In Cruzeiro do Sul, a square area of 4-ha of primary forest was selected to conduct the experiment. In Rio Branco and Candeias do
Forest inventory
The first step, before the cutting of the vegetation, was the conduction of a forest inventory in the central hectare of the three sites. Each specimen had its main characteristics measured (diameter at breast height (DBH), log height, and canopy height). The allometric equation used to estimate the biomass with DBH >10 cm was that of Santos (1996):where FW is the fresh weight (103 kg), and DBH is inserted in meters (m).
The next step was the clearing of the forest,
Forest inventory
The main results of the forest inventory are presented in Table 1 and Fig. 5. The numbers of individuals in the central hectare were 582, 448 and 595, for Cruzeiro do Sul, Rio Branco and Candeias do Jamari, respectively. The total fresh biomass for DBH >10 cm, calculated using Equation (1), was 583.1, 343.8 and 608.3 t, for Cruzeiro do Sul, Rio Branco and Candeias do Jamari, respectively. Most individuals inventoried in the central hectare belonged to the DBH class 10–20 cm. From the 448
Conclusion
Results were described of forest fire experiments conducted in Cruzeiro do Sul, Rio Branco and Candeias do Jamari, cities located in the Western of the Amazon region, Brazil. The main results of the experiments can be summarized as follows:
- (a)
Biomass in Western Amazonia (612.4 ± 142.5 t ha−1) was as heavy as the one in Central Amazonas (685.0 t ha−1), while the one in Northern Mato Grosso was 20.0% lighter.
- (b)
The amount of average carbon contained in the aboveground biomass before the burning, in
Acknowledgements
Funding for this study was provided by the Fundação de Amparo à Pesquisa do Estado de São Paulo – FAPESP, Brazil (Thematic Project number 08/04490-4 and Doctorate Scholarship 13/21231-0).
The burnings in Cruzeiro do Sul and Rio Branco were conducted under permission of the Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq and Instituto de Meio Ambiente do Acre – IMAC, Brazil. The burning in Candeias do Jamari was conducted under permission of CNPq and Secretaria de Estado do
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