Global count reaches 3 trillion trees

Sep 8, 2015

David Zeleny

By Rachel Ehrenberg

There are roughly 3 trillion trees on Earth — more than seven times the number previously estimated — according to a tally1 by an international team of scientists. The study also finds that human activity is detrimental to tree abundance worldwide. Around 15 billion trees are cut down each year, the researchers estimate; since the onset of agriculture about 12,000 years ago, the number of trees worldwide has dropped by 46%.

“The scale of human impact is astonishing,” says Thomas Crowther, an ecologist now at the Netherlands Institute of Ecology in Wageningen who led the study while at Yale University in New Haven, Connecticut. “Obviously we expected humans would have a prominent role, but I didn’t expect that it would come out as the as the strongest control on tree density.”

The previously accepted estimate of the world’s tree population, about 400 billion, was based mostly on satellite imagery. Although remote imaging reveals a lot about where forests are, it does not provide the same level of resolution that a person counting trunks would achieve.

Crowther and his colleagues merged these approaches by first gathering data for every continent except Antarctica from various existing ground-based counts covering about 430,000 hectares. These counts allowed them to improve tree-density estimates from satellite imagery. Then the researchers applied those density estimates to areas that lack good ground inventories. For example, survey data from forests in Canada and northern Europe were used to revise estimates from satellite imagery for similar forests in remote parts of Russia.


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3 comments on “Global count reaches 3 trillion trees

  • @OP – There are roughly 3 trillion trees on Earth — more than seven times the number previously estimated — according to a tally1 by an international team of scientists. The study also finds that human activity is detrimental to tree abundance worldwide. Around 15 billion trees are cut down each year, the researchers estimate; since the onset of agriculture about 12,000 years ago, the number of trees worldwide has dropped by 46%.

    I think that history shows extensive deforestation past and present caused by humans, using, cutting, and burning wood, – together with the grazing of cleared areas by their herds of animals.

    I think the attempt to count individual trees as distinct from areas of forest, is bound to be far from clear, as numerous tree seedlings never make it to maturity, so numbers essentially hinge on what is defined as a tree.

    I do not even know how many trees are in my garden at any one time, but I do weed out inappropriate self sown seedlings from hedges, shrubberies, flower-beds, and vegetable patches.



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  • The previously accepted estimate of the world’s tree population, about 400 billion, was based mostly on satellite imagery.

    Why? Satellite imagery “tells where forests are” but cannot discern individual trees for the purpose of counting. Why attempt an estimate wildly unrelated to actual counts?

    Crowther and his colleagues merged these approaches (sic) [satellite imagery estimates] by first gathering data for every continent except Antarctica from various existing ground-based counts covering about 430,000 hectares. These counts allowed them to improve tree-density estimates from satellite imagery.

    Of course the counts improved because they counted the goddam trees!

    Then the researchers applied those density estimates to areas that lack good ground inventories. For example, survey data from forests in Canada and northern Europe were used to revise estimates from satellite imagery for similar forests in remote parts of Russia.

    Low flying reconnaissance aircraft, covering “remote parts of Russia” could record precise images that separated the forests from the trees whose species, size and density could be accurately measured up close. If the composition factors of remote Russian forests corresponded closely with those in Canada and Northern Europe, then reliable estimates could be easily calculated. Satellite imagery could serve an important function as a rough locator of forested terrain. At the end of the day common sense would dictate that counting the trees (separate from undergrowth – shoots, brush, bushes, ferns and other dense vegetation) would involve credible techniques for identifying trees and actually counting them, allowing of course for necessary but reasonable extrapolations.

    The article plays a shell game keeping up the patter of double-talk.



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