A new study published in the journal Nature claims that a previous satellite-based estimate of the total number of trees on Earth was off by a large margin. Instead of the 400 billion trees previously thought to exist on the planet, there are an estimated 3 trillion. Almost half of these trees are found in tropical and subtropical forests, another quarter of all trees are found in boreal biomes, the vasts forests of Russia and North America, and about 20 percent are in temperate biomes found in Europe, Asia, and the United States.
Humans have had an “overwhelming effect” on trees. Since the beginning of civilization, about 3 trillion trees have been cut down, said the study’s lead researcher Thomas Crowther at Yale University, in an interview with The Guardian. And the high rate of destruction continues, with about 15 billion trees lost each year due to deforestation and the expansion of farmland. In fact, another new study from Global Forest Watch says that 46 million acres of forests were lost just in 2014. The majority of the destruction is in Russia, the United States, Canada, Brazil, and Indonesia, as it has been for more than a decade. But according to Mongabay, an environmental news site, the Democratic Republic of Congo just jumped to near the top of the list this year, as this Sub-Saharan African country lost 1 million hectares of forest.
Crowther and his team found that Russia has the most number of trees, with 640 billion, followed by Canada with 318 billion, and Brazil, with 300 billion. The United States has around 220 billion, while China has 140 billion.
The scientists used nearly a half-million ground-based sensors on every continent, except for Antarctica, to generate a tree map. Tree density estimates were linked with GIS data and other spatial, topographical, and climactic attributes, as well as land use patterns to come up with more detailed estimates.
Crowther and the other researchers conducted the study to create a real baseline for tree planting efforts. They wanted to see whether the Billion Tree Campaign and the many urban million tree campaigns can have any real impact. Crowther told The Guardian that “the message remains that a billion trees is still a huge contribution. I was concerned that providing them [such tree-planting efforts] with this final information might deter efforts and make people go ‘okay, planting a million trees is pointless’ but actually we got the opposite response.” The are efforts underway to even create a global trillion-tree campaign.
As cities ramp up their million-tree campaigns, the discussion has turned where to plant them, so everyone benefits from their health benefits equally. Living in a neighborhood with a lot of trees has shown to boost health and well-being, and some studies have even linked tree coverage with mortality rates. Doctors in Washington, D.C. are now prescribing time in the park to further test the benefits.
A new interactive tool Trees and Health App, created by researchers at Portland State University (PSU) and financed by the U.S. Forest Service, enables urban planners, non-profits, and landscape architects to plot out where trees can have the biggest health impact.
The tool’s approach to data collection and analysis was first developed in Portland, where the team used nearly 150 street-level sensors to measure pollution levels, and then determine how trees reduce the impact of pollution and therefore respiratory problems like asthma. Vivek Shandas, one of PSU researcher, told Smithsonian magazine, “We found that upward of 14 percent of the pollutants are improved by local neighborhood trees and that the kind of trees does matter. Portland is highly coniferous and those [trees] almost act like scrubbers in the summer, but deciduous trees are becoming more dominant in urban landscapes.”
Right now, 13 cities are available for analysis through the tool, but the team plans to add many more. Explore the app.