There are 73,200 species of trees growing on Earth

The Earth is not only a blue planet, but also a green one: large parts of the Earth’s surface are covered with forests. But how many types of trees grow in forests around the world? An international research team has now investigated this. According to their balance, there are 73,000 good species of trees around the world, but at least 9,200 of them can still be discovered and undescribed. The largest variety of tree species can be found in the tropical forests of South America: the species growing there account for about 43 percent of the total tree species diversity, the team reports. At the same time, the proportion of undiscovered rare species can be higher there.

How many species are there on Earth? This is one of the fundamental questions in ecology – one that remains unanswered to this day. Because mankind does not know even a small part of all the living things on this planet. “Even for trees, which are among the largest and most widespread organisms on the planet, enabling so much terrestrial biodiversity and providing us humans with a wealth of ecosystem services, we still don’t know exactly how many species there are,” said Roberto Casola Gatti of the University of Bordeaux and colleagues. Although mid- and high-latitude forests have been relatively well studied, many species-rich forest areas in the tropics remain largely unexplored. “But knowing the species richness and diversity of trees is important in order to maintain the stability and function of ecosystems,” says Gatti.

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Data collected from around the world

To fill this knowledge gap, a team of more than 100 scientists from around the world has compiled and evaluated the most comprehensive and comprehensive data set on tree biodiversity. To do this, they combined information from two global databases, one from the Global Forest Biodiversity Initiative (GFBI) and the other from the TREECHANGE project. For these datasets, tree sets were recorded for tens of thousands of test areas around the world. “Each of these datasets comes from a person who recorded every tree in a piece of the forest and collected information about species, size, and other characteristics,” explains this
Gatti Fellow Jingjing Liang, Coordinator of the Global Forest Biodiversity Initiative.

However, much of the data from such surveys has not yet been published and has only been shared by scientists upon request or as part of special projects. “There was no central repository of the valuable data these people collected,” Liang says. Therefore, he made it his mission to create this central database. With nearly 38 million trees mapped and recorded from 90 countries, the GFBI database is the largest global repository of information about trees in the world to date. By combining this with a second large set of data, the team was able to extend this even further. In the next step, Gatti and colleagues divided the global Earth’s surface into 9,353 grid cells measuring 100 by 100 km and used a statistical method to estimate the number of tree species at the biome, continent and world scale.

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South America has the most tree species

Assessments have shown that there are at least 73,274 species of trees worldwide, of which about 9,200 have yet to be discovered or described. “The absolute number of tree species is much higher than previously assumed, and there are 14.3 percent more species than was known to researchers,” Gatti and colleagues write. The greatest diversity of species can be found in the tropical forests of South America in particular: “43 percent of all tree species grow in South America, followed by Eurasia at 22 percent, Africa at 16 percent and North America at 15 percent,” the team . South America is also the continent with the highest proportion of native species – nearly half of all tree species that grow there are endemic to the continent. There could also be more than 4,000 tree species undiscovered. “Many of them probably grow in the Amazon basin and the Andes and thus in biodiversity hotspots,” explains co-author Peter Reich of the University of Michigan.

The assessments also showed that although many forests are dominated by a few common species, rare species represented by only a few specimens account for about a third of the global diversity of tree species. The researchers reported that some of them only occurred once or twice in the entire database. “This underscores the susceptibility of global forest diversity to human changes, particularly through land use and climate,” says Reich. “Because the survival of rare species is disproportionately threatened by such factors.” The research team hopes that their findings will advance knowledge about tree diversity, but also about forest protection.

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Quelle: Roberto Cazzolla Gatti (Purdue University, West Lafayette) et al, Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2115329119

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