Deforestation and climate change are having a psofound effect on the Amazon basin, shifting it from a carbon sink to a carbon emitter.
The Large-Scale Biosphere-Atmosphere Experiment in the Amazon (LBA) evaluates the connections between climate change, agricultural expansion, logging, and fire risk.
And, concludes the team, there are clear signs of transition to a disturbance-dominated regime in the southern and eastern portions of the Amazon basin.
"Deforestation has moved the net basin-wide budget away from a possible late 20th-century net carbon sink and towards a net source," they say.
he Amazon forest currently holds about 100 billion tones of carbon - 10 years’ worth of global fossil fuel emissions.
The project showed that it can cope with considerable climatic variation from year to year, but that this resilience can be overwhelmed by severe or prolonged drought.
Successful efforts in Brazil to curb deforestation have cut the clearing of forests in the Amazon basin, from nearly 28,000 km2 per year in 2004 to less than 7,000 km2 in 2010.
However, the incidence of fire has not decreased.
"One strong sign of a new disturbance regime is the high number of recent large-scale wildfires, which are a by-product of intentional fires in Brazil’s ‘arc of deforestation.’," says Jennifer Balch, co-author of a paper appearing in Nature.
These fires, she says, are extremely frequent, occurring every few years, compared with every couple centuries in the past.
"The studies in this review, document changes in river flow, sedimentation in rivers, and lengthening of the dry season in the southern and eastern flanks of the Amazon Basin," says lead scientist Eric Davidson of the Woods Hole Research Center.
“Whether similar changes are likely to occur in other parts of the basin will depend on the interplay of management decisions and the impacts of climate change during the next few years and decades.”