Three trillion trees: Study finds there are 7.5 times more trees than previously believed

http://phys.org ^ | September 2, 2015 | Provided by: Yale University

[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

[fwdude]

My question as well. Tiny saplings? And what (species) counts as a tree?

[TomGuy]

That is atrocious!!!

Think of all the CO2 they are pumping into the air. It is going to kill us all!!

It is the fault of that Save-the-Trees movement from several decades ago.

Trees converted to lumber no longer produce CO2.

[madison10]

I have 20 maples growing in my eavestrough do they count?

[Redcitizen]

Bout tree fiddy.

[ETL]

Water vapor accounts for something like 95% of the greenhouse effect on Earth, yet the global governance (gorebull warming) crowd rarely ever mentions it.

[Mastador1]

In 1859 however, the Comstock Lode was discovered in Virginia City, Nevada. During the 1860s Tahoe became the center of a lively commerce involving the silver mines in Virginia City and the Central Pacific Railroad (which was pushing over the Sierra toward the town of Truckee). The Comstock era resulted in large-scale deforestation of the Tahoe Basin, as timber was required to build mine shafts and support growing developments. It is estimated that over 80 percent of the Basin's forests were clear cut during this time.

It doesn't take all that long really to re forest, Tahoe today aside from the damage done by beetle is a thriving full forest.

[The Iceman Cometh]

Science: today’s best guess.

[Red Badger]

Only if you put them in the ground on Arbor Day..................B^)

[Red Badger]

Trees TAKE IN CO2 and GIVE OFF O2....................

[Red Badger]

LOL!.................

[GreyFriar]

I remember a couple decades ago, there was a big complaint that “X number of acres or square kilometers/miles” of Amazonian rain forest was being cut down every day/month/year and that all of that virgin forest was being destroyed. Someone actually took the figures and calculated them and discovered that the numbers had to have been imaginary, because the ‘acres cut’ came to be about twice the land mass of north and south America, or some similar size.

[Leep]

Could be a Global Tree epidemic?

[GeronL]

After admitting their estimates were off by a freaking lot they make another

I bet you dollars to donuts there are more trees in the continental US today than when Columbus first came close to North America.

[tophat9000]

Ah..that a BIG CO2 sink to miss...(as plants breath in/consume CO3)

Ive question the computer climate models on how they model plants vs animal's (flora vs fauna) both are dynamic in growth vs decline... so co2 emitter (fauna) vs co2 consumer (fauna) are always changing

I have thought that it might be flora/fauna cycle driving part of the ice age / warming period cycles

...aka a warm co2 environment would favor fauna..as the plants expand.. they consume co2 emitter o2 to the point that it changes the co2 /o2 balance ...and we going it to a cooling..this lead to a die back of plants and expansion of animals.. who are o2 consumers co2 emitters.. so cycle again to warm.....

[Tenacious 1]

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.

The supercomputer technologies requires some human input. So I believe there may be 15X more trees in the world than originally thought. Did they count the 11 trees I have planted in the last 5 years? I doubt they would show up on satalite.

[Red Badger]

Sting.................I remember that ................

[ETL]

How large does a tree have to be to count?

Interesting question considering how many libs view the start of human life.

[Osage Orange]

I bought 8 tree’s in the last 4 years.....

[Tenacious 1]

Well, that shoots all the Man-Made-Global-Warming computer models to hell. Now they have to re-run the calculations to determine the earths O2 absorbtion rate. That would further decrease man’s .00016 contribution to CO2 collecting in the atmosphere.

....don’t hold your breath.

[Red Badger]

I have more trees on my property now than when I moved here 13 years ago. I cut down the old, diseased, and trash trees and replaced them with new young trees and fruit trees..................