Posted on 09/02/2015 10:56:17 AM PDT by Red Badger
The global map of tree density at the square-kilometer pixel scale. Credit: Crowther, et al
A new Yale-led study estimates that there are more than 3 trillion trees on Earth, about seven and a half times more than some previous estimates. But the total number of trees has plummeted by roughly 46 percent since the start of human civilization, the study estimates.
Using a combination of satellite imagery, forest inventories, and supercomputer technologies, the international team of researchers was able to map tree populations worldwide at the square-kilometer level.
Their results, published in the journal Nature, provide the most comprehensive assessment of tree populations ever produced and offer new insights into a class of organism that helps shape most terrestrial biomes.
The new insights can improve the modeling of many large-scale systems, from carbon cycling and climate change models to the distribution of animal and plant species, say the researchers.
"Trees are among the most prominent and critical organisms on Earth, yet we are only recently beginning to comprehend their global extent and distribution," said Thomas Crowther, a postdoctoral fellow at the Yale School of Forestry & Environmental Studies (F&ES) and lead author of the study.
"They store huge amounts of carbon, are essential for the cycling of nutrients, for water and air quality, and for countless human services," he added. "Yet you ask people to estimate, within an order of magnitude, how many trees there are and they don't know where to begin. I don't know what I would have guessed, but I was certainly surprised to find that we were talking about trillions."
The study was inspired by a request by Plant for the Planet, a global youth initiative that leads the United Nations Environment Programme's "Billion Tree Campaign." Two years ago the group approached Crowther asking for baseline estimates of tree numbers at regional and global scales so they could better evaluate the contribution of their efforts and set targets for future tree-planting initiatives.
At the time, the only global estimate was just over 400 billion trees worldwide, or about 61 trees for every person on Earth. That prediction was generated using satellite imagery and estimates of forest area, but did not incorporate any information from the ground.
The new study used a combination of approaches to reveal that there are 3.04 trillion trees—roughly 422 trees per person.
Crowther and his colleagues collected tree density information from more than 400,000 forest plots around the world. This included information from several national forest inventories and peer-reviewed studies, each of which included tree counts that had been verified at the ground level. Using satellite imagery, they were then able to assess how the number of trees in each of those plots is related to local characteristics such as climate, topography, vegetation, soil condition, and human impacts.
"The diverse array of data available today allowed us to build predictive models to estimate the number of trees at each location around the globe," said Yale postdoctoral student Henry Glick, second author of the study.
The resulting map has the potential to inform scientists about the structure of forest ecosystems in different regions, and it can be used to improve predictions about carbon storage and biodiversity around the world.
"Most global environmental data is thematically coarse," said Matthew Hansen, a global forestry expert from the University of Maryland who was not involved in the study. "The study of Crowther et al. moves us towards a needed direct quantification of tree distributions, information ready to be used by a host of downstream science investigations."
The highest densities of trees were found in the boreal forests in the sub-arctic regions of Russia, Scandinavia, and North America. But the largest forest areas, by far, are in the tropics, which are home to about 43 percent of the world's trees. (Only 24 percent are in the dense boreal regions, while another 22 percent exist in temperate zones.)
The results illustrate how tree density changes within forest types. Researchers found that climate can help predict tree density in most biomes. In wetter areas, for instance, more trees are able to grow. However, the positive effects of moisture were reversed in some regions because humans typically prefer the moist, productive areas for agriculture.
In fact, human activity is the largest driver of tree numbers worldwide, said Crowther. While the negative impact of human activity on natural ecosystems is clearly visible in small areas, the study provides a new measure of the scale of anthropogenic effects, highlighting how historical land use decisions have shaped natural ecosystems on a global scale. In short, tree densities usually plummet as the human population increases. Deforestation, land-use change, and forest management are responsible for a gross loss of over 15 billion trees each year.
"We've nearly halved the number of trees on the planet, and we've seen the impacts on climate and human health as a result," Crowther said. "This study highlights how much more effort is needed if we are to restore healthy forests worldwide."
Researchers from 15 countries collaborated on the study.
More information: Nature, DOI: 10.1038/nature14967
Journal reference: Nature
“”“it’s said that squirrels could travel from tree to tree from the Northeast to the Mississippi without ever having to touch the ground,”””
I don’t believe that for a minute. There was nobody trying to stop forest fires back then, nobody managing any preserves either.
You also bought 8 trees in the past 4 years?
Seems I’ve heard that also, there were less trees 1000’s of years ago than now. That is because back then forest fires just kept burning, now we put them out.
Teaching Math In 1960:
A logger sells a truckload of lumber for $100. His cost of production is 4/5 of the price, or $80. What is his profit?
Teaching Math In 1970:
A logger sells a truckload of lumber for $100. His cost of production is $80. Did he make a profit?
Teaching Math In 1980:
A logger sells a truckload of lumber for $100. His cost of production is $80 and his profit is $20 Your assignment: Underline the number 20.
Teaching Math In 1990:
A logger cuts down a beautiful forest because he is selfish and inconsiderate and cares nothing for the habitat of animals or the preservation of our woodlands. He does this so he can make a profit of $20. What do you think of this way of making a living?
(Topic for class participation after answering the question: How did the birds and squirrels feel as the logger cut down their homes? (There are no wrong answers.)
--From a passed around e-mail
Look at pictures of civil war battlefields and look at the same places today, big difference. Yeah in the USA Eastern seaboard there are a lot more trees.
Yes, Pecan, peach, apple, pear, fig and some shade trees..................
Lucky you to live in what sounds like a nice ‘country’ setting. I’m stuck here in miserable New York City.
Oh, THOSE trees! We had classified them as shrubbery and spontaneous topiary outgrowths.
Old growth forests don’t take in much CO2, so since we have loads more trees than we thought, we should (to save the Environment, dontcha know) start a MASSIVE old forest cutdown program. If the enviros were honest, thats what would happen, oh that and Nuclear Now... but.. mostly crickets from the left.
So it looks like the eco-Idiots were wrongo again. Bwahahahahahahaaaaaaaaaaaaaaaaaaaaaa.
Just a residential neighborhood, unincorporated, with a large corner lot and room for a few good trees. Had to cut down several old trees and hurricane fodder..................
B-b-but where would the spotted owls live?????...............
Impossible! The rain forests all disappeared years ago, at the rate they said they were being cut down!
It’s the TREE’S, oh my god, Global warming, it’s the TREES!
The above statement is a spin that supercomputers modeling climate change spit out garbage when they are fed garbage.
I must have at least 2,000 trees or so on my 20 acres. There are new ones every year, and if I didn’t mow the lawn, the lawn would be forest.
I have 5 enormous pecan trees I cannot collect all the nuts from—I used to have an old fella come round every Fall to collect them but he passed. Now I might pick up a bucket or two for myself but the rest are for the squirrels, dogs (yes my dogs LOVE pecans and squirrels, it’s like a twofer for them) or they grow into seedlings. I mow hundreds each year.
Tree huggers really need to get busy or a lot of trees will never get a hug.
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