The Carbon Balance of Tropical Forests is a Matter of Life and Death
Living trees take carbon dioxide out of the air as they grow, and dead trees put carbon back into the air as they decompose. This study, seven years in the making, for the first time quantifies tropical forest disturbance and mortality at a continental scale from branch falls through vast blow-downs caused by windstorms. The study confirms that, in its natural state, the Amazon forest removes more carbon from the atmosphere than it emits, therefore reducing the carbon dioxide content of the atmosphere and ameliorating global warming.Using a combination of remote sensing data, the authors found that each year, dead Amazonian trees emit over 1 petagram (1 billion metric tons) of carbon to the atmosphere. Because there is no universally accepted estimate of Amazon carbon absorption, the researchers ran a model combining their tree-mortality data with censuses of forest growth and other information, using different scenarios to cover the uncertainties in the data. In every scenario, the absorption of carbon by living trees prevailed, indicating that the net effect of the Amazon is to absorb carbon. Until now, scientists have estimated tree deaths for the Amazon basin from limited observations of about 100 forest plots comprising about 1 hectare (2.47 acres) in area. On these plots, the forest removes more carbon than it emits. The scientific community has been vigorously debating how well the plots represent all the processes in the huge Amazon region since the discovery in the 1990s that large areas of the forest can be killed off by intense storms in events called blowdowns.
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