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3 Trillion: Study Finds Many, Many More Trees Than Previously Estimated

Even with billions of trees being cut down every year, a new study estimates there are seven-and-a-half times more trees on Earth than previously believed: 3.04 trillion, to be precise — or roughly 422 trees per person.

An international team of researchers used tree density information from forests around the world, satellite imagery and supercomputer computations to map tree populations worldwide at the square-kilometer level. The results were much higher than expected.

"Trees are among the most prominent and critical organisms on Earth, yet we are only recently beginning to comprehend their global extent and distribution," Thomas Crowther, a postdoctoral fellow at the Yale School of Forestry & Environmental Studies and lead author of the study, said in a statement.

"They store huge amounts of carbon, are essential for the cycling of nutrients, for water and air quality, and for countless human services," he added. "Yet you ask people to estimate, within an order of magnitude, how many trees there are and they don't know where to begin. I don't know what I would have guessed, but I was certainly surprised to find that we were talking about trillions."

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The largest forest areas, by far, are in the tropics, which are home to about 43 percent of the world's trees, the researchers found. About 24 percent are in boreal regions and 20 percent in temperate regions.

The 3 trillion figure is seven and a half times more than the previous estimate of 400 billion trees worldwide as of 2005. That estimate, which translates to about 61 trees for every person, was made by a professor of environmental studies at Evergreen State College in Olympia, Washington, based on NASA satellite images.

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Though the new figure is remarkably higher than expected, the news is not all bright.

The researchers note that humans are having an “overwhelming” negative impact on tree populations across the world. Due to deforestation, land-use policies and forest management practices, an estimated 15 billion-plus trees are being cut down each year. In fact, the study concludes that the global number of trees has fallen by roughly 46 percent since the start of human civilization.

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"We've nearly halved the number of trees on the planet, and we've seen the impacts on climate and human health as a result," Crowther said. "This study highlights how much more effort is needed if we are to restore healthy forests worldwide."

The study, "Mapping tree density at a global scale," was published Wednesday in the journal Nature.