The number of trees on Earth is seven times more than previously thought, and many more than the amount of stars in the Milky Way, a new study revealed.
Combining ground-based surveys with satellite imagining, an international team of scientists has determined there are approximately 3 trillion trees on Earth, far exceeding the previous estimate of about 400 billion, according to Nature, an international weekly journal of science.
The researchers also estimate that the amount of trees being cut down annually is around 15 billion, and that the number of trees worldwide has dropped by 46 percent since the onset of agriculture some 12,000 years ago.
"It's not like we discovered new trees," Thomas Crowther, an ecologist from the Netherlands Institute of Ecology in Wageningen who led the study while at Yale, told Nature. "Rather, we added another layer of information that allowed us to revise much of the previous estimates."
Previous estimates were based on mostly satellite imagery, but this study included thousands of people counting trees all over the world, providing a more accurate count, a count that is truly amazing compared to the estimated 100 billion stars in the Milky War.
Nature explains in the video:
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.
Improved population estimates could help resource managers to weigh up the economic benefits that forests provide in terms of water purification, soil conservation and other functions against those of harvesting or clearing trees for farmland, says ecosystems-services ecologist Becky Chaplin-Kramer of Stanford University in California. "It's great when we can fill in gaps like this," she says.
"All this data helps our understanding of where endangered species will be able to live, how water is cycled in an ecosystem or how much carbon dioxide is being absorbed from the atmosphere," the video says. "It also helps us work out what we ought to be doing to preserve and replenish our planet's forests."
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