Abstract
Abstract. A simulation model based on satellite observations of monthly vegetation greenness from the Moderate Resolution Imaging Spectroradiometer (MODIS) was used to estimate monthly carbon fluxes in terrestrial ecosystems of Brazilian Amazon and Cerrado regions over the period 2000–2002. The NASA-CASA (Carnegie Ames Stanford Approach) model estimates of annual forest production were used for the first time as the basis to generate a prediction for the standing pool of carbon in above-ground biomass (AGB; g C m−2) for forested areas of the Brazilian Amazon region. Plot-level measurements of the residence time of carbon in wood in Amazon forest from Malhi et al. (2006) were interpolated by inverse distance weighting algorithms and used with CASA to generate a new regional map of AGB. Data from the Brazilian PRODES (Estimativa do Desflorestamento da Amazônia) project were used to map deforested areas. Results show that net primary production (NPP) sinks for carbon varied between 4.25 Pg C yr−1 (1 Pg=1015 g) and 4.34 Pg C for the region and were highest across the eastern and northern Amazon areas, whereas deforestation sources of CO2 flux from decomposition of residual woody debris were higher and less seasonal in the central Amazon than in the eastern and southern areas. Increased woody debris from past deforestation events was predicted to alter the net ecosystem carbon balance of the Amazon region to generate annual CO2 source fluxes at least two times higher than previously predicted by CASA modeling studies. Variations in climate, land cover, and forest burning were predicted to release carbon at rates of 0.5 to 1 Pg C yr−1 from the Brazilian Amazon. When direct deforestation emissions of CO2 from forest burning of between 0.2 and 0.6 Pg C yr−1 in the Legal Amazon are overlooked in regional budgets, the year-to-year variations in this net biome flux may appear to be large, whereas our model results implies net biome fluxes had actually been relatively consistent from year to year during the period 2000–2002. This is the first study to use MODIS data to model all carbon pools (wood, leaf, root) dynamically in simulations of Amazon forest deforestation from clearing and burning of all kinds.
Highlights
Greenhouse gas emissions from tropical deforestation and land cover change are among the most uncertain components of the global carbon cycle
Global net primary production (NPP) of vegetation can be predicted using the relationship between leaf reflectance properties and the absorption of photosynthetically active radiation (PAR), assuming that net conversion efficiencies of PAR to plant carbon can be approximated for different ecosystems or are nearly constant across all ecosystems (Running and Nemani, 1988; Goetz and Prince, 1998)
The Enhanced Vegetation Index (EVI) has been found useful in estimating absorbed PAR related to chlorophyll contents in vegetated canopies (Zhang et al, 2005), and has been shown to be highly correlated with processes that depend on absorbed light, such as gross primary productivity (GPP) (Xiao et al, 2004; Rahman, 2005)
Summary
Greenhouse gas emissions from tropical deforestation and land cover change are among the most uncertain components of the global carbon cycle. As recommended by Ramankutty et al (2007), our NASA-CASA modeling framework (Potter et al 1999, 2003, and 2009) has been designed to estimate historical as well as current monthly patterns in plant carbon fixation, living biomass increments, nutrient allocation, litter fall and decomposition, long-term decay of slash pools, soil CO2 respiration, and soil nutrient mineralization before, during, and after deforestation events in the tropics To our knowledge, this is the first study to take full advantage of both Landsat and MODIS land cover products to make annual NBP estimates for the Amazon region. All model carbon pools (wood, leaf, and root) have been altered dynamically in the simulations of clearing and burning anywhere and everywhere that deforestation has been mapped out by PRODES results
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