Posts Tagged ‘tree inventory’

12,000 years of agriculture has only reduced tree numbers by 46%

September 3, 2015

There is a new paper in Nature which tries to count the number of trees in the world.

Crowther, T. W. et al., Mapping tree density at a global scale, Nature (2015)

They find that there are 3.04 trillion trees which is about 7 times larger than was previously thought. They further estimate that in spite of 12,000 years of agriculture, the number of trees in the world has only reduced by 46%.

But then I heard the lead author, Thomas Crowther, being interviewed on the BBC today. I was less than impressed by his apparent lack of common sense. “The scale of human impact is astonishing” he says.


There has been a less than 50% reduction of tree-numbers in 12,000 years of agriculture, with all the forest clearing that entails, to feed 7 billion people. A human impact of less than 0.0038% per year (or 3.8% per 1000 years) is claimed to be “astonishing”.

He also claims that their results do not impact “carbon science”. Again, Really?

Seven times as many trees as thought before is 7 times as much bio-mass existing as trees, which leads to 7 times as much carbon inventory locked-up in trees as thought before. It means 7 times more trees die every year than was previously thought. Which makes man-made carbon emissions an even smaller fraction (c. 4%) of natural carbon emissions.

Crowther sounded like a vacuum cleaner salesman talking up his product. He kept emphasising the importance of his paper while denying that it had any implications for “politically correct science”. The estimate of the number of trees is interesting and could be something to build on for carbon cycle calculations. It also suggests that alarmism about bio-diversity of trees is ill founded. But some of their conclusions are just stupid and geared to getting more funding by demonstrating “political correctness”.

Reasonably interesting science but with idiot conclusions.

Oh dear!

Abstract: The global extent and distribution of forest trees is central to our understanding of the terrestrial biosphere. We provide the first spatially continuous map of forest tree density at a global scale. This map reveals that the global number of trees is approximately 3.04 trillion, an order of magnitude higher than the previous estimate. Of these trees, approximately 1.39 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.61 trillion in temperate regions. Biome-level trends in tree density demonstrate the importance of climate and topography in controlling local tree densities at finer scales, as well as the overwhelming effect of humans across most of the world. Based on our projected tree densities, we estimate that over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization.

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