Mapping and quantifying post-fire carbon budget in Amazonia


Global climate change and the large-scale loss of the tropical forests are probably the most urgent of contemporary environmental problems. Some global circulation models suggest that Amazonia may be vulnerable to extreme drying in response to circulation shifts induced by global warming, with a significant probability of enhanced dry seasons in eastern Amazonia.

In the event of long-term drying and increased drought frequency in the Amazon region, the leakage of deliberate fires into forest areas is likely to be the major agent of forest transformation rather than changes in forest ecology and physiology. This process has an important influence on the global carbon cycling by affecting vegetation structure, changing carbon pools and fluxes, and causing feedbacks to the atmosphere, but it is thus far poorly quantified. The lack of systematic information (spatial and temporal) on these processes is a critical limitation when estimating the magnitude of this carbon source and consequent maintenance of the Amazon forest biome and its ecosystem function. The 21st century is bringing ongoing forest clearance, degradation and fragmentation, coupled with a probability of more frequent drought.

In this context, fires in Amazonian forests are almost certain to increase in occurrence: Hence my main research aim in this fellowship is to combine information from multi-temporal satellite images with extensive field data on the component processes of the net ecosystem productivity (NEP) to obtain the first detailed and spatially extensive assessment of the long-term effect of forest fires on the carbon balance of Amazonian forests. The specific aims are:

  1. Generate the first map of the fire-affected forests in the Brazilian Amazon.
  2. Quantify the amount of carbon being emitted, uptake and moved from and among forest compartments at different time-scales and at different fire frequency and intensity.
  3. Calculate the carbon budget of Amazonian forests taking into account the effect of forest fires, and understand how this variation is controlled by climate and deforestation rates.
  4. Understand how the carbon balance varies temporally and spatially because of forest fires.

To achieve the aims of this proposal, the first step will be to analyze multi-temporal satellite remote sensing images to map the scars of Amazonian forests affected by fire and quantify the frequency of fire occurrence in these areas. To better understand the variation of the intensity of the fires, the mapped burn scars will be stratified by distance from the nearest ignition source (deforested areas, roads), as the intensity of the fires decreases with the increased distance from the ignition source. Finally, a biomass map will be used to identify different forest classes in the Amazon.

The maps will then be merged in one single map showing the forest stratified by biomass, fire frequency and intensity. This will characterize the spatial variability of fire damage in the region that is likely to influence the variation of carbon budget of Amazonia. This map will be the basis for defining the areas that will be investigated in detail in the field and will be also used in a later stage to extrapolate field data to the whole Amazon. The second step will tackle the effect of different fire frequency and intensity on carbon budget. This will involve a compilation of existing field data and direct measurements in key field sites selected in the stratification procedure, of the component processes of the carbon balance or net primary productivity (NEP), which is the difference between the CO2 assimilated by the vegetation through photosynthesis and the CO2 released by the ecosystem through the respiration process. This will be quantified in terms of aboveground biomass, coarse wood debris, stand fine litter layer, fine roots and soil carbon and respiration fluxes. These measurements will provide detailed information on the amount of carbon being emitted, absorbed and moved from and among forest compartments at different time-scales depending on the severity of the fire damage.

I have been successfully employing and developing the methods to measure carbon stocks and fluxes in my current postdoctoral research in intact Amazonian and Andean forests and I am confident this is a reliable method to be implemented in these areas. Once the data from the different sources have been prepared and analysed, the logical next step is to integrate the datasets in order to understand the annual Amazon-wide variation of the component processes of NEP in the fire-affected areas.

Two main approaches will be tested initially: (1) a zonal average method, where, having the stratified map of burn intensity and frequency, the biomass map and knowing the behaviour of NEP components in each one of the classes, an average value of NEP can be associated to each class; and (2) a decision tree method, which consider binary decision rules, that can be implemented by combining information about the fire classes and empirically-calibrated relationships between NEP and its component processes with rainfall, biomass and forest type. At this stage all the information will be available for calculating the carbon budget of Amazonian forests, taking into account the effect of forest fires and for investigating its temporal and spatial variation, which will be done in the next step.

The ultimate goal of this work is to arrive at annual spatially explicit values of uptake, release and the net balance of carbon in fire-affected forest sites in recent years, to quantify the relative influences of the component processes that determine this net carbon balance and to understand how climate variation and human activities through deforestation, affects its spatial and temporal patterns.

The general result of this study can then be used to inform large-scale estimates of carbon emissions from the tropics and to help decision makers to define priority areas for conservation and to plan a more sustainable occupation of Amazon region. The detailed results will strongly contribute towards calibrating and validating models that quantify fire emissions from Amazonia. This work will also involve the local community, students and researchers and will be important for the exchange of information in order to develop site-specific conservation and management practices in this region. Beyond the local impact of this research, the knowledge on carbon dynamics and on the stability of Amazonian forests can be extremely important for implementing “Avoided Deforestation” and forest regrowth strategies, as potential mechanisms for climate change mitigation. In the context of the Kyoto Protocol and the Clean Development Mechanism (CDM), this is becoming an issue of increasing financial and political relevance.

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