"With a clearer understanding of the relative risks to the Amazon forest, we conclude that direct human impacts, such as forest clearance for agriculture or mining, should remain a focus of conservation policy," Lewis said. "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."
Dick and his colleagues used a molecular clock approach to determine the ages of 12 widespread Amazon tree species, including the kapok and the balsa. Then they looked at climatic events that have occurred since those tree species emerged. In general, they inferred that the older the age of the tree species, the warmer the climate it has previously survived.
The researchers determined that nine of the tree species have been around for at least 2.6 million years, seven have been present for at least 5.6 million years, and three have existed in the Amazon for more than 8 million years.
"These are surprisingly old ages," Dick said. "Previous studies have suggested that a majority of Amazon tree species may have originated during the Quaternary Period, from 2.6 million years ago to the present."
Air temperatures across Amazonia in the early Pliocene Epoch (3.6 million to 5 million years ago) were similar to Intergovernmental Panel on Climate Change projections for the region in 2100 using moderate carbon-emission scenarios. Air temperatures in the late Miocene Epoch (5.3 to 11.5 million years ago) were about the same as IPCC projections for the region in 2100 using the highest carbon-emission scenarios.
The 12 tree species used in the study are br
|Contact: Jim Erickson|
University of Michigan