South America is home to nearly half of the 9,000 tree species unknown to science

  • The most comprehensive survey of tree life on Earth has just been published, showing that there are some 9,000 species that scientists have yet to describe.
  • Nearly half of these unknown trees are found in South America, which in turn accounts for 43% of the estimated 73,000 trees found on Earth, according to the study.
  • Nearly 150 researchers from around the world collaborated in the study, which increases the previous estimate for the total number of tree species by 14%.
  • The study authors say that unidentified species are mostly rare and more vulnerable to the risk of extinction, so there is an urgent need for stronger protection and enforcement of environmental laws.

“Since childhood I have always been fascinated by the diversity of living beings on our planet and I dreamed of working to explore unexplored places on Earth and discover the unknown species that live there”, says Roberto Cazzolla Gatti. “Then, as a biologist, in recent years I have been dedicated to biodiversity issues, and one of them is how to estimate it with as little error as possible and how to protect it.

With this goal in mind, Cazzolla Gatti, from the University of Bologna in Italy, conducted a study that resulted in the most comprehensive georeferenced global tree survey ever.

The result of the work surprised even the almost 150 researchers from all over the world who took part in it. It took years to create this gigantic database, involving the participation of experts of all kinds, as well as the help of supercomputers and artificial intelligence.

Previous estimates put the number of tree species worldwide at around 64,000. This new study, however, bumps that figure up 14%, to 73,300 species. Of these, 9,000 are still unknown to science, and therefore very rare.

“The result left us stunned,” says Cazzolla Gatti. “We never imagined that there would be so many tree species to discover. In fact, this study offers the scientific community, and humanity in general, more knowledge about their incredible diversity. C It’s even more incredible to think that we don’t even know them all yet [in 2022]!”

Renowned for its biodiversity, South America is home to the largest number of tree species, according to the study, at 43% of the total. Next comes the Eurasia region (22%), Africa (16%), North America (15%) and Oceania (11%).

South America is also the continent with most trees still undescribed by science – somewhere around 4,000.

“The richest areas are where the Andes meet the Amazon,” says Oliver Phillips, professor of tropical ecology at the University of Leeds, UK. “That’s where the diversity is high and the number of undescribed species is probably higher.

“Due to the complex topography, climates and geology, there is more diversity and many species will have a smaller distribution,” he adds. “That makes them harder to discover and also more vulnerable.”

Tropical forest specialist and coordinator of the Amazon Forest Inventory Network (Rainfor), Phillips is one of 148 authors of the study published in early February in the Proceedings of the National Academy of Sciences (PNAS), which also includes several Brazilian researchers.

Amazon rainforest in the Tambopata River region of Peru. Image by Joseph King (CC BY-NC-ND 2.0).

Amazon basin: a biodiversity hotspot

At least 31,000 tree species grow in South America alone. Many of them are endemic to the continent, meaning they do not occur anywhere else on the planet. Their habitats include the tropical and subtropical forests of the Amazon, in countries like Peru, Colombia, Ecuador, Venezuela, Bolivia, and Brazil, as well as the high altitudes of the Andes region.

In this verdant vastness – there are around 390 billion trees in the Amazon basin alone – two-thirds of the species are considered very rare.

“These are species that number less than a million individuals,” says co-author Wendeson Castro, a botanist at the Federal University of Acre in Brazil. This is the case in this case Pouteria sessilisCommonly called abiu and endemic to Peru, says Castro. “We are still very clueless about how many species we have and how many we are losing,” he adds.

That’s why the new study, actually an inventory of tree life on Earth, is so relevant. With the certainty that we still lack knowledge about the biodiversity of the world’s forests, and in particular those of South America, it is essential to put in place stricter protection and inspection laws, say the authors.

“Our results reinforce the absolute necessity of preserving tropical forests,” says co-author Jorcely Barroso, professor at the Federal University of Acre. “Unidentified species are mostly rare and more vulnerable to the risk of extinction. Having a better understanding of these numbers and possible locations is key to developing protection strategies, even without knowing them.

Barroso says the large number of as-yet-undocumented species likely to occur in the Amazon Basin and the Andes-Amazon transition zone makes these areas a priority for conservation.

Unknown and endangered

Despite the good news that there are more tree species on Earth than previously thought, one of the main concerns the study highlights is the impact of human activities on their preservation.

For example, the climate of South American forests, where most unknown species are found, has been stable for several centuries. But in the face of more recent phenomena, such as climatic extremes, it is feared that the flora of this region will find it difficult to adapt to the impacts of these changes, such as prolonged droughts and more frequent fires.

“They are more vulnerable to habitat loss, especially since their range is small to begin with,” says Phillips. “But if we can protect certain elevation corridors of forest habitat, species are more likely to migrate uphill to avoid the heat and drought of climate change.”

Where the Amazon merges into the foothills of the Andes in Ecuador. Image by Dallas Krentzell (CC BY 2.0).

The researchers say the species going extinct isn’t the only problem. In the face of all these vulnerabilities and threats, trees could cease to provide the essential environmental services that humanity needs to survive and the planet needs to stay in balance.

“We often think of trees and forests as just our oxygen producers, but they are actually so much more than that,” says Cazzolla Gatti. “Without them, we would have no clean water, no safe mountain slopes, no habitat for many animals, fungi and other plants. We would lose the Earth’s most biodiverse ecosystems, the sinks of our excess carbon dioxide and purifiers of our polluted air.

He adds that if we are to protect the diversity of trees and the incredible richness of other plant and animal species related to them, we must immediately stop deforestation and forest degradation and start viewing forests as untouchable ecosystems that deserve to be protected, like coral reefs.

As an example, Cazzolla Gatti states: “Timber, pulp and paper should only be harvested from man-made plantations and not from natural or semi-natural forests.

“If we stop burning forests as ‘biofuels’, buying products containing palm oil, using tropical wood for our homes, eating large quantities of meat every day, replacing nature by urbanized and industrial areas, and by killing and polluting the fauna that this tree preserved ecosystems, we will have time to discover new species and allow our planet to have a more balanced existence, as well as to the human species itself.


Cazzolla Gatti, R., Reich, PB, Gamarra, J. GP, Crowther, T., Hui, C., Morera, A., … Liang, J. (2022). The number of tree species on Earth. Proceedings of the National Academy of Sciences, 119(6), e2115329119. doi:10.1073/pnas.2115329119

Ter Steege, H., Pitman, N. CA, Sabatier, D., Baraloto, C., Salomão, RP, Guevara, JE, … Silman, MR (2013). Hyperdominance of Amazonian tree flora. Science, 342(6156), 1243092. doi:10.1126/science.1243092

Banner image of rainforest in the central Amazon region, by Neil Palmer/CIFOR.

This story was reported by the Brazil team at Mongabay and first published here on our Brazil site on March 1, 2022.


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