An interesting new study estimates there are more than 3 trillion trees on Earth, about seven and a half times more than previous estimates. The results, recently published in the journal Nature, provide the most comprehensive assessment of tree populations ever produced. The study used a combination of approaches revealing that there are roughly 422 trees per person. The number may sound like a lot of trees, however, human-driven deforestation has had a staggering impact on the world’s flora. The research suggests the total number of trees has plummeted by roughly 46% since the start of human civilization and more than 15 billion additional trees are lost to human-related causes each year. 
“Trees are among the most prominent and critical organisms on Earth, yet we are only recently beginning to comprehend their global extent and distribution. They store huge amounts of carbon, are essential for the cycling of nutrients, for water and air quality, and for countless human services,” said Thomas Crowther, a postdoctoral fellow at the Yale School of Forestry & Environmental Studies and lead author of the study.
The highest densities of trees were found in the boreal forests in the sub-arctic regions of Russia, Scandinavia, and North America. But the largest forest areas, by far, are in the tropics, which are home to about 43% of the world’s trees.
“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.”
Crowther added that one of the most dominant themes of the study is how large an effect humans are having on the tree population on the planet. "Human activity came out as the strongest control on tree density across all biomes," he said. "It really highlights how big of an impact humans are having on the Earth on a global scale."