A major reason for alarm over the rate and magnitude of deforestation
in Brazil has been concern that the reduction in vegetation releases c
arbon dioxide (CO2) and other greenhouse gases (GHG) that may contribu
te to global climate change. While deforestation releases CO2 and othe
r GHG, however, tree growth elsewhere absorbs atmospheric carbon (C) t
hrough photosynthesis. discussions of CO2 releases from tropical defor
estation have tended to focus on gross releases and have generally not
considered the effects of carbon uptake. The objective of this paper
is to examine the net C balance for Brazil, by estimating both CO2 - C
release and uptake. Our approach was to construct a generalized conce
ptual model of ecosystem C cycling that could be applied to any vegeta
tion type and can be quantified with available data. the primary C poo
ls in the model are the atmosphere, live vegetation, litter and coarse
woody debris, and soil. Fluxes are represented as transfer between th
ese pools that occur as a result of land use change, disturbance or re
covery from past disturbance by plant growth and accumulation of organ
ic matter. To estimate ecosystem areas, we used and adapted the most r
ecently completed and current vegetation map available (Stone et al. i
n press). The primary sources for C density data were a report compile
d by Olson et al (1983) and a subsequent version. We also used an alte
rnative C density for closed moist forest from Brown and Lugo (1992).
These forests play a major role in Brazil's C balance, but there is so
me uncertainty regarding their C density. We attempted to bracket this
uncertainty by using both high and low values. We also used published
data to calculate flux estimates. A major flux in Brazil's C budget i
s release to the atmphere resulting from deforestation. In 1990, 1.38
x 10(6) ha of closed forest were cleared in Brazil. Additionally, abou
t 1.0 x 10(6) ha of cerrado woodland also cleared. We also estimated t
hat 0.35 x 10(6) ha of secondary forest were cleared that year. Total
C releases for the country as a whole were 174 - 233 x 10(6) tc/yr. Th
e difference was caused mostly by differing estimates in the C density
of closed tropical moist forests, which resulted in different fluxes
from deforestation and burning. Net changes in pool sizes of our C bud
get model varied. The total vegetation C pool decreased by 160 - 240 x
10(6) tc/yr. The soil pool also lost C, about 80 x 10(6) tc/yr as a r
esult of disturbance from forest clearing and intensive agriculture. H
owever, the litter/coarse woody debris pool increased by 70 - 90 x 10(
6) tc/yr. This increase was due to transfers from the vegetation pool
due to clearing of closed tropical moist forest. Total gross C uptake
by the system was 100 x 10(6) tc/yr of which 60 x 10(6) was addition t
o litter and soil pools in secondary forets. Total C releases were 120
- 150 x 10(6) tC/yr from deforestatio/burning and 150 - 180 x 10(6) t
C/yr from decomposition. Most of the C released from burning was deriv
ed from above-ground vegetation but a significant amount also came for
m litter and coarse woody debris, including from reburning of residual
logs and pastures.