Using radiocarbon dating methods, the team, which includes UC Irvine's Susan Trumbore, found that up to half of all trees greater than 10 centimeters in diameter are more than 300 years old. Some of the trees, Trumbore said, are as much as 750 to 1,000 years old. Study results appear in the online early edition of the Proceedings of the National Academy of Sciences.
"Little was known about the age of tropical trees, because they do not have easily identified annual growth rings," added Trumbore, a professor of Earth system science. "No one had thought these tropical trees could be so old, or that they grow so slowly."
And for Trumbore, who studies how forests and the atmosphere exchange carbon, these discoveries can have implications for the role the Amazon plays in determining global carbon dioxide levels. Carbon dioxide is a greenhouse gas implicated in accelerated global warming and the focus of international efforts to curb its atmospheric levels.
Because their trees are old and slow-growing, the Amazon forests, which contain about a third of all carbon found in land vegetation, have less capacity to absorb atmospheric carbon than previous studies have predicted. Although some of the largest trees also grow the fastest and can take up carbon quickly, the vast majority of the Amazon trees grow slowly.
"In the Central Amazon, where we found the slowest growing trees, the rates of carbon uptake are roughly half what is predicted by current global carbon cycle models," Trumbore said. "As a result, those models -- which are used by scientists to understand how carbon flows through the Earth system -- may be overestimating the forests' capacity to remove carbon dioxide from the atmosphere."