When it comes to the world’s forests, two of the commonly asked questions are “How many trees are are on Earth?” and “How many trees are cut down each year?” A new study proposes answers: three trillion and 15.3 billion.
The research, published today in the journal Nature, is based on a combination of satellite imagery, on-the-ground inventories, and computer modeling led by Thomas Crowther of the Netherlands Institute of Ecology. Crowther conducted the research while at Yale University.
“Trees are among the most prominent and critical organisms on Earth, yet we are only recently beginning to comprehend their global extent and distribution,” Crowther was quoted as saying in an article posted on Yale’s web site.
“They store huge amounts of carbon, are essential for the cycling of nutrients, for water and air quality, and for countless human services. 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.”
Three trillion trees is far higher than the previous leading estimate of 400 billion trees. The wide discrepancy is the result of the more comprehensive methodology used by the research team.
“The diverse array of data available today allowed us to build predictive models to estimate the number of trees at each location around the globe,” said Yale postdoctoral student Henry Glick, second author of the study.
The research broke down tree cover by biome and country, finding the highest density in boreal forests, which altogether house 750 billion trees, or about a quarter of the world’s total. The largest extent of forests exist in the tropics, which have 1.3 billion trees, or 43 percent of the planet’s trees. The differences make intuitive sense given the high diversity and larger size of trees in the tropics versus sub-arctic regions.
By country, Russia had the most trees at 642-698 billion. It was followed by Canada (318-361 billion trees), Brazil (302-338 billion), the United States (222-228 billion), and China (140-178 billion). The highest density among countries with significant amounts of forest cover was Finland, with more than 72,000 trees per square kilometer. It was followed by Slovenia, Sweden, and Taiwan.
The study also estimated current and historical rates of tree cover loss. It said that the number of trees worldwide has fallen 46 percent since the dawn of agriculture 12,000 years ago and more than 15 billion trees are felled every year.
That loss has significant implications for the planet in terms of climate change, biodiversity, and human well-being, according to Crowther.
“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,” he said. “This study highlights how much more effort is needed if we are to restore healthy forests worldwide.”
Article published by Rhett Butler on September 3, 2015 on Mongabay