Amazon comes under fire
The Amazon rainforest stores around 100 billion tonnes of carbon in its biomass, the equivalent of more than 10 years' worth of emissions from fossil fuels. But the region has undergone major changes recently, experiencing deforestation and climate variability. With that in mind, over the last 20 years the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) has looked at some of the processes involved.
"The Amazon region is under multiple pressures simultaneously – land-use change due to agricultural expansion, global climate change, regional climate change induced by the regional land-use change, and widespread use of fire," Eric Davidson of the Woods Hole Research Centre, US, told environmentalresearchweb. "We show how these pressures interact."
Davidson and colleagues recently reviewed some of the findings of the NASA-funded contribution to the LBA in Nature.
According to Davidson, areas that have already had some forest clearing tend to have more sources of fire ignition in the cleared pastures, slash-and-burn agriculture, and charcoal production activities. "If the climate is drier and the remaining forest under water stress, the fires may spread into forests that had not previously experienced fire," he said. "We also try to sort out these pressures geographically, showing how the greatest changes can already be detected on the southern and eastern flanks of the Amazon, where most change has occurred and where the climate is already naturally dry and getting drier."
The human population of the Brazilian Amazon has risen dramatically, from 6 million in 1960 to 25 million in 2010. At the same time, forest cover has decreased to around 80% of its original area. There are recent signs of improvement, however: deforestation rates have dropped from nearly 28,000 sq km per year in 2004 to less than 7,000 sq km per year in 2011.
"Brazil has successfully reduced rates of deforestation but not incidence of fire," said Davidson. "One implication is the need to control fire better and to find technologies for pasture management and small-scale agriculture that do not rely on fire."
The team reckons that the interactions between deforestation, fire and drought can lead to losses of carbon storage and changes in regional precipitation patterns, and river discharge. "Although the basin-wide impacts of land use and drought may not yet surpass the magnitude of natural variability of hydrologic and biogeochemical cycles, there are some signs of a transition to a disturbance-dominated regime," they write in Nature. "These signs include changing energy and water cycles in the southern and eastern portions of the Amazon basin."
As well as improving scientific knowledge, Davidson believes that the LBA project's training of a new generation of Brazilian scientists is now "providing tremendous human resources and expertise to inject science into the public policy discourse".