Absent of deforestation, Amazon rainforest might survive global warming.
Estimated genetic ages of trees in the study. Photo by Rhett A. Butler
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.
Christopher Dick of the University of Michigan and the Smithsonian Tropical Research Institute (STRI), Simon Lewis of the University of Leeds, Mark Maslin of University College London, and Eldredge Bermingham of STRI analyzed the age of 12 widely distributed Amazon tree species. They found that nine of the species emerged prior to the Pliocene Epoch some 2.6 million years ago, seven dated to the Miocene Epoch (5.6 million years ago), and three were more than eight million years old.
The findings indicate that many Amazon tree species have survived warm periods in the past and are therefore likely to survive climate change projected for the year 2100. Air temperatures in the Amazon during the early Pliocene were similar to Intergovernmental Panel on Climate Change projections for the region in 2100 under a moderate carbon emissions scenario, while temperatures in the late Miocene (5.3-11.5 million years ago) are roughly what the IPCC forecasts under a highest carbon emissions scenario.
The study seems to be at odds with other research suggesting that many Amazon trees would face extinction from higher temperatures alone. For example a 2008 study published in the Proceedings of the National Academy of Sciences (PNAS) projected up to 50 percent of “rare” species across the Amazon could disappear.
 Canopy tree in Peru. Photo by Rhett A. Butler |
However the authors caution that the results do not indicate that Amazon trees are out of the woods yet — other environmental and ecological changes still leave the region highly vulnerable.
“The past cannot be compared directly with the future. While tree species seem likely to tolerate higher air temperatures than today, the Amazon forest is being converted for agriculture and mining, and what remains is being degraded by logging, and increasingly fragmented by fields and roads,” said Lewis in a statement. ” Species will not move as freely in today’s Amazon as they did in previous warm periods, when there was no human influence. Similarly, today’s climate change is extremely fast, making comparisons with slower changes in the past difficult.”
The authors therefore suggest conservation policies focused on preventing deforestation. They also recommend cuts to global greenhouse gas emissions.
“With a clearer understanding of the relative risks to the Amazon forest, we conclude that direct human impacts – such as forest clearances for agriculture or mining – should remain a focus of conservation policy,” said Lewis. “We also need more aggressive action to reduce greenhouse gas emissions in order to minimize the risk of drought and fire impacts to secure the future of most Amazon tree species.”
The Amazon is Earth’s largest rainforest. Nearly two-thirds of the Amazon lies within the borders of Brazil, which has made great progress in reducing deforestation since 2004. However deforestation in Amazon countries outside Brazil is holding relatively steady.
CITATION: Dick, C. W., Lewis, S. L., Maslin, M. and Bermingham, E. (2012), Neogene origins and implied warmth tolerance of Amazon tree species. Ecology and Evolution. doi: 10.1002/ece3.441
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