New research has provided the most accurate count yet for the number of trees on Earth: 3.04 trillion. The finding, with 95% accuracy, is about eight times more than previous estimates, but suggests that the number of trees has plummeted 46% since the dawn of human civilization 11,000 years ago – with the number once being above six trillion.
The study, published in the journal Nature, was conducted by an international team of researchers and led by Yale University. The tree count was made using a combination of satellite imagery and more than 400,000 ground measurements, with the researchers defining a tree as “a plant with woody stems larger than 10 centimeters [four inches] diameter at breast height.”
In a press conference, lead author Thomas Crowther, a postdoctoral fellow at the Yale School of Forestry & Environmental Studies (F&ES), noted that previous studies only looked at plants larger than 50 centimeters (20 inches) in diameter. Nonetheless, the latest findings could help map endangered species, show how water is recycled and reveal how much carbon dioxide is being absorbed from the atmosphere.
Perhaps most significantly, the study highlights the dramatic effect humanity is having on the natural world.
"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 in a statement. “This study highlights how much more effort is needed if we are to restore healthy forests worldwide.”
Data from the study could be useful in working out how much carbon is stored in terrestrial vegetation. "In the study, we show that there is a positive relationship between the amount of trees in an area and the amount of carbon storage," Crowther told IFLScience, but he noted that "this relationship was not strong because the highest densities of trees are often dominated by a large number of small trees that don’t store much carbon."
The findings are visualized in the video above. Nature/YouTube.
Breaking down the findings, 1.39 trillion trees were in tropical and subtropical forests, 0.74 trillion in boreal regions and 0.61 trillion in temperate regions. Thanks to the data on the ground, the researchers were able to measure the density of trees in forests around the world to come to their accurate figures.
The study looked at tree levels over the last 12 years, and found that there was a gross loss of more than 15 billion trees a year, and a net loss of 10 billion when regrowth was taken into account. Crucially, humans were found to be "one of the dominant regulators of trees," Crowther said in the press conference. "The one consistent factor is the negative impact of humans."
Another outcome of the study was on campaigns to plant more trees, such as the UN's Billion Trees Campaign. According to the findings, planting one billion trees is just 1/3000th of the total number on Earth, suggesting greater efforts are needed to manage Earth’s ecosystem.
Overall, the message is clear: We are having a drastic effect on Earth’s ecosystem. There are currently 422 trees per person in the world but, if current trends continue, that will fall to 214 in 150 years. It’s a sobering thought to realise just how much of an impact we are having on this relatively tiny ball of rock we call a planet.