How many tree species are there on our planet? The answer is now provided by the most comprehensive inventory of global tree diversity to date. According to this, at least 73,200 different tree species grow on earth, which is a good 14 percent more than previously estimated. The greatest diversity can be found in the tropical forests of South America with 43 percent of all tree species. However, many of these species are very rare and therefore particularly threatened, as the research team reports.
Whether in the tropics, in temperate latitudes or in the taiga of the far north: trees are found almost everywhere on earth. It is estimated that more than three trillion of these plants grow on our planet. They form the “green lungs” of our planet and are important climate buffers. At the same time, forests provide the habitat for countless other animal and plant species.
How many types are there?
But one question has so far remained largely unanswered: How many tree species exist on our planet? “Even for trees, which are among the largest and most widespread organisms on the planet, we still don’t know exactly how many species there are,” say Roberto Cazzolla Gatti of Purdue University and his colleagues. Although the forests of the middle and higher latitudes have been studied relatively well, many species-rich forest areas in the tropics have not.
To fill these gaps, Gatti and his team have compiled the most comprehensive inventory of arboreal biodiversity to date. To do this, they relied on two global databases whose data sets contain information from tens of thousands of test areas around the world. With around 38 million trees mapped and recorded from 90 countries, the Global Forest Biodiversity Initiative (GFBI) database is the largest global repository of information on trees worldwide to date.
The team combined this data with a second large data collection from the TREECHANGE project and used a statistical method to estimate the number of tree species at biome, continent and world level.
A good 14 percent more tree species than expected
The result: there are at least 73,274 tree species worldwide, of which around 9,200 have not yet been described or named. “The absolute number of tree species is thus considerably higher than previously assumed, there are 14.3 percent more species than were known to researchers,” write Gatti and his colleagues. However, even this number is probably still incomplete and too low because the data situation is very sparse in some regions.
The greatest diversity of trees is found in the tropics: “The highest values come from the tropical and subtropical wet forest biomes,” the researchers report. “Around two-thirds of all tree species already known occur in such forests on all five continents.” The rainforests are not only hotspots of tree diversity, but are also probably home to most of the as yet undiscovered species.
South America has the greatest diversity
When comparing the continents, by far the most tree species grow in South America: “Our data on continental tree diversity show that around 43 percent of all tree species grow in South America,” report Gatti and his colleagues. Most of these trees are found in the Amazon basin and in the forested areas on the edge of the Andes. According to the researchers’ estimates, even more tree species could be undiscovered there than anywhere else.
Closely linked to this is the large number of rare tree species in this region: Worldwide, rare species represented by only a few specimens make up around a third of the global tree species diversity – and they are also concentrated in the forests of the tropics. “This underscores the vulnerability of global forest diversity to anthropogenic changes, especially through land use and climate,” says co-author Peter Reich from the University of Michigan. “Because the survival of rare species is disproportionately threatened by such factors.”
Important also beyond the trees
According to the scientists, knowledge about these rare and potentially threatened tree species, but also about the entire arboreal diversity, can now help to better protect them. “In-depth knowledge of tree species richness and diversity is key to maintaining ecosystem stability and functionality,” says Gatti. In addition, this is also an important piece of the puzzle in the overall biodiversity of the planet.
“Our results demonstrate both the lack of knowledge we still have about the trees in our global forest ecosystems and the value of approaches to fill these gaps,” states the research team. “Because this provides us with fundamental insights into the diversity of life on our planet and the protection that we need.” (Proceedings of the National Academy of Sciences, 2022; doi: 10.1073/pnas.2115329119)
Quelle: University of Michigan, Purdue University