Abstract
The CASA (Carnegie-Ames-Stanford) ecosystem model based on satellite greenness observations has been used to estimate monthly carbon fluxes in terrestrial ecosystems from 2000 to 2009. The CASA model was driven by NASA Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation cover properties and large-scale (1-km resolution) disturbance events detected in biweekly time series data. This modeling framework has been implemented to estimate historical as well as current monthly patterns in plant carbon fixation, living biomass increments, and long-term decay of woody (slash) pools before, during, and after land cover disturbance events. Results showed that CASA model predictions closely followed the seasonal timing of Ameriflux tower measurements. At a global level, predicting net ecosystem production (NEP) flux for atmospheric CO2 from 2000 through 2005 showed a roughly balanced terrestrial biosphere carbon cycle. Beginning in 2006, global NEP fluxes became increasingly imbalanced, starting from -0.9 Pg C yr-1 to the largest negative (total net terrestrial source) flux of -2.2 Pg C yr-1 in 2009. In addition, the global sum of CO2 emissions from forest disturbance and biomass burning for 2009 was predicted at 0.51 Pg C yr-1. These results demonstrate the potential to monitor and validate terrestrial carbon fluxes using NASA satellite data as inputs to ecosystem models.
Highlights
The emission of CO2 from deforestation and other land cover changes is among the most uncertain components of the global carbon cycle
The CASA model was driven by NASA Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation cover properties and large-scale (1 km resolution) disturbance events detected in biweekly time series data
Flux estimates from eddy-correlation analysis were obtained from AmeriFlux tower flux sites that could meet certain criteria for CASA model comparisons
Summary
The emission of CO2 from deforestation and other land cover changes is among the most uncertain components of the global carbon cycle. A recent review of previous work on estimating carbon emissions from vegetation change by Ramankutty et al [8] pointed to the importance of considering ecosystem dynamics following land cover conversion, including the fluxes from the decay of products and slash pools, and the fluxes from either newly established agricultural lands or regrowing forest. This review suggested that accurate carbon-flux estimates should consider historical land-cover changes over at least the previous 20 years. Such results can be highly sensitive to estimates of the partitioning of cleared carbon into instantaneous burning vs long-time scale dead woody pools. The main objective of the present study was to quantify the major controls on carbon flux patterns and processes terrestrial ecosystems worldwide, using NASA satellite data products to drive models of net ecosystem production (NEP) and detect large-scale ecosystem disturbance, leading to detailed estimates of net biome production (NBP)
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