The net carbon flux due to deforestation and forest re-growth in the Brazilian Amazon: analysis using a process-based model

We developed a process-based model of forest growth, carbon cycling and land-cover dynamics named CARLUC (for CARbon and Land-Use Change) to estimate the size of terrestrial carbon pools in terra firme (nonflooded) forests across the Brazilian Legal Amazon and the net flux of carbon resulting from forest disturbance and forest recovery from disturbance. Our goal in building the model was to construct a relatively simple ecosystem model that would respond to soil and climatic heterogeneity that allows us to study the impact of Amazonian deforestation, selective logging and accidental fire on the global carbon cycle. This paper focuses on the net flux caused by deforestation and forest re-growth over the period from 1970 to 1998. We calculate that the net flux to the atmosphere during this period reached a maximum of ~0.35 PgC yr^1 (1 PgC= 1 *10^15 gC) in 1990, with a cumulative release of ~7 PgC from 1970 to 1998. The net flux is higher than predicted by an earlier study (Houghton et al., 2000) by a total of 1 PgC over the period 1989-1998 mainly because CARLUC predicts relatively high mature forest carbon storage compared with the datasets used in the earlier study. Incorporating the dynamics of litter and soil carbon pools into the model increases the cumulative net flux by~1 PgC from 1970 to 1998, while different assumptions about landcover dynamics only caused small changes. The uncertainty of the net flux, calculated with a Monte-Carlo approach, is roughly 35% of the mean value (1 SD).