2 Carbon Losses and Sequestration with Land Use Change in the Humid Tropics

The role of tropical forests in the global carbon (C) cycle has been debated over the past 20 years, as several estimates of the flux of carbon dioxide (CO 2) from 42 Thematic Research tropical deforestation have been proposed (Houghton et al. 1987; Detwiler and Hall 1988; Brown et al. 1993). Current estimates indicate that land use change in the trop-ics released 1.7 (0.6–2.5) Gt C/yr, compared with 5.4 ± 0.3 Gt C/yr from fossil fuel emissions (ipcc 2001). This flux has been attributed primarily to deforestation in the tropical zone, with Asia and Latin America accounting for more than 80 percent of the flux (Houghton 1997). However, a recent analysis of the net carbon flux from the Brazilian Amazon suggests that carbon sources created by deforestation are off-set by carbon sinks from the undisturbed forest and regrowing secondary vegetation (Houghton et al. 2000). As noted by DeFries et al. (1999), reducing the uncertainty of estimates of CO 2 emissions caused by land use change is key to balancing the globa