A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

The Net Carbon Flux Due to Deforestation and Re-growth in the BrazilianAmazon: Comparing Process-Based and Bookkeeping ApproachesAuthors: Adam Hirsch a* , William S. Little b , and Richard A. Houghton aa The Woods Hole Research Center, P.O. Box 296, Woods Hole, MA, 02543, USAb The Woods Hole Oceanographic Institute, Woods Hole, MA, 02543, USA*Corresponding Author. Email: ahirsch@whrc.orgAbstract: Recent work (Houghton et al., Nature 2000) suggests that the net flux ofcarbon to the atmosphere from deforestation and forest re-growth in the BrazilianAmazon averaged approximately 0.2 Pg C (1 Pg = 1 billion metric tons) per year from1989-1998. That study assumed a linear biomass accumulation for forests growing onabandoned agricultural land and a constant ratio of agricultural area abandoned toprimary forest area cleared each year. We test the impact of these assumptions on theland-use carbon flux by changing the model used in the Houghton et al. (2000) study intwo ways. First, we predict mature forest biomass and re-growth rates across theBrazilian Amazon using a process-based ecosystem model that is driven by observedradiation, climate, and soil characteristics. Second, we calculate rates of agriculturalabandonment and re-clearing of secondary forest from temporal changes in land-coverderived from satellite data. For the 1990s, the process-based model yields slower regrowthrates than the Houghton et al. (2000) study, but a much larger area of re-growingforest. The net impact of these changes is to lower the predicted net source of carbon dueto deforestation and re-growth during the period 1989-1998 from 0.2 Pg C per year to0.15 Pg C per year.