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.”
A mortality map of the Amazon near Manaus, Brazil based on Landsat satellite images shows the spatial pattern of tree mortality.
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.
“These climate change signals will start popping out of the noise faster and faster as the years go on,” Chambers said. “So, what’s going to happen to old-growth tropical forests? On one hand they are being fertilized by some unknown extent by the rising CO2 concentration, and on the other hand a warming climate will likely accelerate tree mortality. So which of these processes will win out in the long-term: growth or death? Our study provides the tools to continue to make these critical observations and answer this question as climate change processes fully kick in over the coming years.”
CITATION: Jeffrey Q. Chambers et al. The steady-state mosaic of disturbance and succession across an old-growth Central Amazon forest landscape. PNAS January 28, 2013, doi: 10.1073/pnas.1202894110
(12/24/2012) The impact of a major drought in the Amazon rainforest in 2005 persisted far longer than previously believed, raising questions about the world’s largest tropical forest to cope with the expected impacts of climate change, reports a new study published in the journal Proceedings of the National Academy of Sciences.
(12/14/2012) Some Amazon rainforest tree species are more than eight million years old found a genetic study published in the December 2012 edition of Ecology and Evolution.
(12/12/2012) Severe drought conditions in 2010 appear to have substantially increased tree mortality in the Western Amazon, a region thought largely immune from the worst effects of changes occurring in other parts of the world’s largest rainforest, reported research presented last week at the fall meeting of the American Geophysical Union (AGU). The findings suggest that the Amazon may face higher-the-expected vulnerability to climate change, potentially undercutting its ability to help mitigate greenhouse gas emissions by absorbing carbon dioxide through faster growth.
(11/23/2012) Forests worldwide are at ‘equally high risk’ to die-off from drought conditions, warns a new study published this week in the journal Nature. The study, conducted by an international team of scientists, assessed the specific physiological effects of drought on 226 tree species at 81 sites in different biomes around the world. It found that 70 percent of the species sampled are particularly vulnerable to reduction in water availability. With drought conditions increasing around the globe due to climate change and deforestation, the research suggests large swathes of the world’s forests — and the services they afford — may be approaching a tipping point.
(01/26/2012) Already on the decline worldwide, big trees face a dire future due to habitat fragmentation, selective harvesting by loggers, exotic invaders, and the effects of climate change, warns an article published this week in New Scientist magazine. Reviewing research from forests around the world, William F. Laurance, an ecologist at James Cook University in Cairns, Australia, provides evidence of decline among the world’s ‘biggest and most magnificent’ trees and details the range of threats they face. He says their demise will have substantial impacts on biodiversity and forest ecology, while worsening climate change.
(02/03/2011) In 2005 the Amazon rainforest underwent a massive drought that was labeled a one-in-100 year event. The subsequent die-off of trees from the drought released 5 billion tons of CO2. Just five years later another major drought struck. The 2010 drought, which desiccated entire rivers, may have been even worse according to a new study in Science, adding on-the-ground evidence to fears that climate change may inevitably transform the world’s greatest rainforest.
(08/12/2009) Old growth forests in the Amazon store nearly 10 billion tons of carbon in dead trees and branches, a total greater than global annual emissions from fossil fuel combustion, according to scientists who have conducted the first pan-Amazon analysis of “necromass.”
(04/13/2009) An experimental study of pinon pines at Biosphere 2 in Arizona shows that an increase in temperature makes the species more susceptible to die-off during drought. When temperatures were increased by 4 degrees Celsius (7.2 degrees Fahrenheit), the piñon pines died 28 percent faster than trees which experienced drought-conditions at current temperatures, according to a new study published in Proceedings of the National Academy of Sciences (PNAS).
(03/05/2009) Drought in the Amazon is imperiling the rainforest ecosystem and global climate, reports new research published in Science. Analyzing the impact of the severe Amazon drought of 2005, a team of 68 researchers across 13 countries found evidence that rainfall-starved tropical forests lose massive amounts of carbon due to reduced plant growth and dying trees. The 2005 drought — triggered by warming in the tropical North Atlantic rather than el Niño — resulted in a net flux of 5 billion tons of carbon dioxide (CO2) into the atmosphere — more than the combined annual emissions of Japan and Europe — relative to normal years when the Amazon is a net sink for 2 billion tons of CO2.