WASHINGTON - A first-of-its-kind examination of the Amazon's trees found that as many as half the species may be threatened with extinction or heading that way because of massive deforestation. Among the more than 5,000 tree species in deep trouble: the ones that produce Brazil nuts and mahogany.

An international team of 158 scientists found that depending on the degree to which deforestation comes under control in the next 35 years, between 36 and 57 percent of the 16,000 tree species in the tropical rainforest area would be considered threatened. The study is published in Friday's edition of Science Advances.

The range rests on whether cutting down the region's forest continues at the rate of the late 20th and early 21st centuries or slows to lesser levels proposed in 2006, study authors said. If deforestation continues at the same pace, nearly 8,700 tree types are in trouble, but the number of species at risk could be as low as 5,500 if nations are able to cut back as planned, said study coauthor Nigel Pitman, from the Field Museum in Chicago.

"We've never had a good idea of how many species are threatened in the Amazon," Pitman said Friday. "Now with this study, we have an estimate."

About 15 years ago, the Amazon was losing about 11.6 million square miles of forest a year, said Tim Killeen, a scientist from Agteca Amazonica in Bolivia. But that figure has dropped to about 3.8 million square miles a year, he said.

Killeen said the tree that produces Brazil nuts is seriously under threat, while "mahogany is commercially extinct throughout the Amazon." He said that means there's no more industry harvesting the wood, but some trees exist.

Duke University ecologist Stuart Pimm, who was not part of the study, praised the work as sensible and important.