Saturday, September 5, 2015

Scientists Redetermine The Number Of Trees On Earth

Earth Sciences

Sub-Saharan Africa: “An impala strikes a pose under a forest canopy in Zimbabwe.”
Photo Credit: Morkel Erasmus; Getty Images
Source: NPR


An article, by Nell Greenfieldboyce, in NPR says that after a two-year study, scientists have completed the most extensive and exhaustive census of the world’s tree populations. The number of trees that inhabit the earth is three trillion, which is almost eight times more than the previous estimate of 400 billion trees. This equates to about 422 trees per human inhabitant.

In “Tree Counter Is Astonished By How Many Trees There Are” (September 2, 2015), Greenfieldboyce writes about how Thomas Crowther, a Yale Climate & Energy Institute postdoctoral fellow at the Yale School of Forestry & Environmental Studies (F&ES), found an accurate way to count trees.
“We used ground-sourced information,” says Crowther. “All of the information that went into our models was generated from people standing on the ground counting numbers of trees in a given area. And so we could relate this information to what the satellites are telling us.”
To get a better estimate, his team took advantage of the fact that countries produce detailed forest inventories. “It definitely couldn't have been done without all of those huge national forest inventories and thousands of people going out, collecting tree information around the world,” says Crowther.
Using information from around 400,000 forest plots, the researchers painstakingly crunched a ton of numbers. And then it was time for the computer to spit out the final total. “We all gathered in a room, it was a very exciting time,” remembers Crowther. “We'd been working toward it for two years.”
He says the huge number astonished them. And then he got a little worried.“My fear is that a lot of people might think, ‘OK, well, there's loads of trees, so who cares about the environment, there's plenty left! No worries!’ What I’d highlight is that it's not like we’ve discovered new trees,” he says. “We’ve just generated a new number that will help us to understand the global forest.”
The detailed map shows that most of the trees are found in the tropical regions of the Amazon basin and sub-Saharan Africa, in the boreal forests of Canada along the strip near the U.S. border and in the sub-arctic regions of Russia and Scandinavia, Not surprising, these are the regions that have a large forestry industry.

The boreal forests have the greatest tree densities, but the tropical regions possess the most number of trees. As an example, the Amazon basin has a tree density of one million or more trees per square kilometer. The largest geographical area for trees are the tropics, says Kevin Dennehy for Yale News. “which are home to about 43% of the world’s trees. (Only 24% are in the dense boreal regions, while another 22% exist in temperate zones.).”

As this study confirms, there are still many trees, for example, in the lush rain-forests of Brazil (where 60 per cent of it resides), but other studies show that these now cover only six per cent of the earth, where two thousand years they covered 14 per cent. The importance of the Amazon basin as the home of an important ecosystem for the planet cannot be overemphasized.

Although there are a lot more trees than we had once thought, human activity continues to reduce their numbers by 15 billion each year. We have cut their number in half in the last few thousand years, the greatest activity taking place in the last two hundred years—coinciding with increased mechanization and industrialization.

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For more, go to [NPR]

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