There are more than 3 trillion trees in the world, according to a fascinating study recently released in the journal Nature. The good news: That's more than seven times earlier estimates of 400 billion trees. The bad news: Humans have cut those numbers by 47 percent since the start of civilization.

But how do you count that many trees? And where are they?

Scientists calculated what's called "tree wealth" or "tree resources" based on estimates of the number of trees in every country in the world in relation to various factors including the country's physical size and population.

The world's overall tree leader is Russia, with 642 billion trees, reports The Washington Post, which analyzed the data presented by researchers. Next is Canada with 318 billion trees and Brazil with 302 billion. The United States comes in fourth with 228 billion trees.

Other countries with significant tree wealth include China (140 billion), the Democratic Republic of the Congo (100 billion), Indonesia (81 billion) and Australia (77 billion).

GALLERY: The world's oldest living trees

Having lots of trees provides many benefits, as the Post points out:

They filter water, combat air pollution, sequester huge amounts of carbon that would otherwise reside in the atmosphere, and even, it appears, contribute to human psychological and health benefits. Indeed, large parts of the world population depend on forests for food.

Plus, there's the emotional benefit.

“I think people inherently value trees,” said Clara Rowe, one of the study's authors and a recent graduate of the Yale School of Forestry and Environmental Studies. “In the days since our study was published, we’ve heard from individuals all over the world who are concerned about forest resources in their countries.”

global tree density mapThis tree density map of the world shows where Earth is rich with tree cover and where it's not. (Photo: Nature)

What it means

It's little surprise that larger countries with the most land often have the most trees. That's why researchers wondered if it was more valuable to measure "tree density," which looks at the most trees per square kilometer. With that measurement, desert countries have the lowest tree densities.

Researchers also considered the number of trees per person and found that large, northern countries like Russian and Canada were very tree-rich, while desert countries were tree-poor.

Although it has been suggested that wealthier countries often have more trees, the Nature researchers (and their data) disagree. They found no correlation between economic status and trees.

But researchers believe that knowing tree wealth can be a good starting point for improving the overall tree situation.

“Ultimately, we hope that our study encourages more specific metrics for understanding forest resources,” Rowe told the Washington Post. “Countries should ask themselves: How old are our forests? How much carbon do they store? How diverse are our trees and the species they shelter? But for now, tree number is a great place to start.”

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.