Ecosystem modeling and dynamic effects of deforestation on trace gas fluxes in Amazon tropical forests

• Published in: Forest ecology and management 2001-10, Vol.152 (1), p.97-117
• Main Authors: Potter, Christopher, Davidson, Eric, Nepstad, Daniel, Carvalho, Claudio Reis de
• Format: Article
• Language: English
• Subjects: Amazon forest; Biological and medical sciences; Carbon; Deforestation; Forestry; Fundamental and applied biological sciences. Psychology; General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; Nitrogen; rain forests; Trace gas flux
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/S0378-1127(00)00593-4

To improve predictive capabilities for water, carbon, and nitrogen gas fluxes in the Amazon region, we evaluated the performance of the NASA–CASA simulation model for tropical ecosystem biogeochemistry against independent flux measurements from two Amazon forest sites located in the Brazilian states of Rondônia and Pará. Refinements of this ecosystem model include stand water balance equations, moisture holding and retention capacity for Amazon soils, and addition of a dynamic deforestation sequence to include land use change as a factor in simulations of tropical ecosystem fluxes. Results suggest that model predictions for evapotranspiration and soil water content are consistent with the overall range and seasonal changes in measured values at the two forest sites selected as test cases. The predicted carbon balance from the model implies that relatively undisturbed Amazon forest ecosystems may be large net sinks for atmospheric carbon, with annual net ecosystem production values on the order of 200 g C m −2 per year. Measured fluxes of soil N 2O for the two Amazon forests closely match our model prediction for the Pará forest, but not for the Rondônia site, suggesting that process algorithms controlling nitrogen trace gas fluxes, particularly in relatively sandy tropical soils will require further study. In terms of net ecosystem carbon fluxes during deforestation and for 2 years afterward, the model predicts that these sites switch from being a net sink for carbon to a substantial source following the large loss of biomass from simulated burning. During crop regrowth simulation in the first year after deforestation, the net source of carbon to the atmosphere is nearly 1.6 kg C m −2 per year, a flux magnitude roughly equivalent to 10 years of undisturbed CO 2 sink fluxes in the Amazon forest. Compared to the primary forest that was cut and burned, predicted changes in soil nitrogen cycling lead to a doubling in annual emissions of N 2O gas during the first year following deforestation, with lower emissions thereafter. Implications for scaling up these model predictions to the Amazon forest region are discussed with reference to necessary improvements in land cover, land use, and soils classifications for the area.