Storm- And Drought-Linked Tree Mortality In Amazon Forests 9-17% Higher Than Generally Believed

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This image taken from a helicopter shows the same blowdown region a few years after the event that is imaged on the Landsat mortality map. The regrowing vegetation has covered up most of the downed trees, but some tree stems are still visible. Courtesy of the authors.

The rate of tree mortality in the Amazon rainforest due to storm damage and drought is 9-17 percent higher than conventionally believed, reports a study published in the Proceedings of the National Academy of Sciences (PNAS).

Comparing Landsat satellite images with on-the-ground observations, researchers from the Lawrence Berkeley National Laboratory, INPA, Tulane University, and other institutions found that roughly half a million dead trees across a 1000-square-mile plot of Brazilian rainforest went unaccounted for over a 20 year period. The fundings suggest that carbon emissions from storm damage could be higher than previously estimated.

"If these results hold for most tropical forests, then it would indicate that because we missed some of the mortality, then the contribution of these forests to the net sink might be less than previous studies have suggested," said lead author Jeffrey Chambers of the U.S. Department of Energy's Lawrence Berkeley National Laboratory, noting that a single storm in 2005 killed hundreds of millions of trees across the Amazon. "An old-growth forest has a mosaic of patches all doing different things. So if you want to understand the average behavior of that system you need to sample at a much larger spatial scale over larger time intervals than was previously appreciated. You don't see this mosaic if you walk through the forest or study only one patch. You really need to look at the forest at the landscape scale."

With climate models projecting stronger storms and more intense droughts as temperatures rise in the tropics, the results raise concerns about rainforests' ability to store carbon, according to Chambers, who went on to add that the study will help improve the understanding of forests' role in the climate system.

EDIT

http://news.mongabay.com/2013/0201-tree-die-off-amazon.html