There are about 9,000 undiscovered species of trees on Earth.

Our planet can host some 9,000 species of trees yet to be discovered. A third of them would be rare species with a restricted population both in number and area. This is one of the results of the first estimate of the richness of tree species worldwide, according to the University of Bologna (Italy) in a statement.

The study is published this Monday in the magazine PNAS and it is the result of a three-year international project in which the approximately 73,000 species of trees that currently exist on Earth have been counted.

A first team of researchers compiled the most extensive databases of tree species. In this mapping operation, approximately 40 million trees belonging to 64,000 species were identified. It involved 150 scientists from around the world and was carried out within the framework of the Global Forest Biodiversity Initiative (GFBI).

Based on this preliminary result, the researchers carried out complex statistical analyzes using artificial intelligence and the supercomputer of the Laboratory for Advanced Computing and Artificial Intelligence (FACAI) at Purdue University in Indiana (USA).

A puzzle

Once these analyzes and calculations were completed, the researchers estimated that our planet has approximately 73,300 species of trees, 14% more than are currently known.

"Counting the number of tree species around the world is like a puzzle with pieces spread across the globe. We, the Global Forest Biodiversity Initiative (GFBI), have solved it as a team, sharing each of our pieces," says Professor Jingjing Liang, coordinator of the GFBI Purdue-Hub and co-author of the article.

According to these results, there are still 9,000 unknown species, of which 40% could be in South America, more specifically in the two biomes made up of "grasslands, savannahs and thickets" and "tropical and subtropical forests" of the Amazon and the Andes. Approximately 3,000 of these species are rare, endemic to the continent and populate tropical and subtropical areas.

This work highlights the richness of terrestrial ecosystems and, at the same time, underlines how forest biodiversity is extremely vulnerable to human-induced changes – from land use to climate crisis – and how rare species They are the most at risk.

"A broad knowledge of the richness and diversity of trees is key to preserving the stability and functionality of ecosystems," explains Roberto Cazzolla Gatti, first author of this study and professor at the Department of Biological, Geological and Environmental Sciences at the University of Bologna.

"Until today, our data relating to large areas of the planet were very limited and were based on observation on the ground and on lists of species that covered different areas. These limitations were detrimental to a global perspective of the issue," he adds.

"To obtain a reliable estimate of biodiversity, you have to pay attention to the number of rare species that are currently known, those that were found once, twice or three times during field sampling," explains Cazzolla Gatti. "Indeed, most species are quite common and numerous, there are some rare ones and even fewer are the ones we don't know about. If many species have been observed only a few times, there are probably many rare species that haven't been documented yet." .

The scientists applied this approach to available databases, both continental and global, estimating the number of unknown tree species and identifying areas of the world where they are likely to be discovered.

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