A study published in Nature’s online journal this past week estimates that there are just over three trillion trees on Earth. Previous estimates counted only 400 billion, eight times smaller than the new number.
The team used a combination of mass ground survey data and satellite pictures to establish their number.
Of the approximately 3,040,000,000,000 trees, the scientists estimate that 1.39 trillion are in the tropics and subtropics, 0.61 trillion are in temperate regions and 0.74 trillion in the boreal forests (coniferous forests of the northern latitudes).
As of 2013, Calvin’s campus is home to over 3,500 of the Earth’s nearly three trillion trees. This high density led to Calvin’s recognition as a tree-friendly campus through the “Tree Campus USA” program in April 2013.
Thomas Crowther, the lead scientist on the study, and his team estimate that the new total means that there are approximately 420 trees per person on the planet.
Dr. Crowther cautions that the higher number does not mean anything has changed.
“It’s not like we’ve discovered a load of new trees; it’s not like we’ve discovered a load of new carbon,” he told the BBC. “We’re simply describing the state of the global forest system in numbers that people can understand and that scientists can use, and that environmental practitioners or policymakers can understand and use.”
The study does make it clear that humans have a strong influence on the number of trees on Earth. The team estimates that humans remove close to 15 billion trees per year, while only planting five billion.
“The net loss is about a third of a percent of the current number of trees globally,” co-author Dr. Henry Glick told the BBC. “That doesn’t seem to be an insignificant portion and should probably give us cause for considering the role that deforestation is playing in changing ecosystems.”
Dr. Glick believes that the net loss of trees could increase with the planet’s exploding population, telling the BBC, “[W]here tree losses are often tied to timber supplies and land-use conversion for agriculture, as the global human population grows, we may see the net loss increase as well.”
To drive this point home, a comparison with estimates of ancient forest cover suggests that humans have already removed close to three trillion trees since the last ice age, which occurred some 11,000 years ago.
“Europe used to be almost covered by one giant forest and now it’s almost entirely fields and grasslands,” Dr. Crowther told the BBC. “Humans are absolutely controlling tree densities.”
Some, such as Dr. Nathalie Pettorelli from the Zoological Society of London, believe that this study is unlikely the last effort to conduct a global tree count.
“It may be important to acknowledge that these first estimates produced by Crowther and colleagues are derived from data primarily collected in Europe and North America, with [for example] very little information collected in the Congo basin, China, Australia or India,” Dr. Pettorelli told the UK Science Media Centre.
“As more information becomes available for these countries, it might be interesting to refine the estimates and check that key processes shaping spatial variability in tree density have not been overlooked.”
