Scientists Count the World’s Tree Species (Spoilers: It’s a Bunch)

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By Will Dunham

WASHINGTON (Reuters) – From the monkey puzzle tree in Peru to the Tasmanian blue gum in Australia, from the baobabs in Madagascar to the giant sequoias in California – the world is blessed with an abundance of tree species. How many? A new study has the answer.

Researchers on Monday unveiled the world’s largest forest database, which includes more than 44 million individual trees in more than 100,000 locations in 90 countries – helping them calculate there are approximately 73,300 species of trees on Earth.

This figure is about 14% higher than previous estimates. Of that total, it’s estimated that about 9,200 exist based on statistical models but have not yet been identified by science, with a large portion of them growing in South America, the researchers said.

South America, home to the vastly biodiverse Amazon rainforest and vast Andean forests, has been home to 43% of the planet’s tree species and the largest number of rare species at around 8,200.

Trees and forests are much more than mere oxygen producers, said Roberto Cazzolla Gatti, professor of biodiversity and conservation at the University of Bologna in Italy and lead author of the study, published in the journal Proceedings of the National Academy of Sciences.

“Without trees and forests, we would not have clean water, safe mountain slopes, habitats for many animals, fungi and other plants, the most biodiverse terrestrial ecosystems, sinks for our excess carbon dioxide, purifiers of our polluted air, etc.,” Gatti said.

“Indeed, our society often regards forests as just pieces of wood and trees as natural resources, ignoring their fundamental role for humanity in providing ecosystem services that lag behind purely economic – albeit important – wood, paper and pulp production. It is from trees and forests that humanity derives inspiration, relaxation, spirituality and essentially the meaning of life,” Gatti added.

It has been determined that there are about 27,000 known tree species and 4,000 yet to be identified in South America. Eurasia has 14,000 known and 2,000 unknown species, followed by Africa (10,000 known/1,000 unknown), North America including Central America (9,000 known/2,000 unknown), and Oceania including Australia (7,000 known/2,000 unknown).

“By setting a quantitative benchmark, our study can contribute to tree and forest conservation efforts,” said study co-author Peter Reich, a forest ecologist at the University of Michigan and the University of Minnesota.

“This information is important because tree species are becoming extinct due to deforestation and climate change, and to understand the value of this diversity, we need to know what’s even there before we lose it,” Reich said. “Tree species diversity is key to maintaining healthy, productive forests and important to the global economy and nature.”

That study didn’t count the total number of individual trees worldwide, but a 2015 study led by one of the co-authors put that number at about 3 trillion.

The new study identified global tree diversity hotspots in the tropics and subtropics of South America, Central America, Africa, Asia and Oceania. It was also found that about a third of the known species can be classified as rare.

The researchers used methods developed by statisticians and mathematicians to estimate the number of unknown species based on the abundance and presence of known species. Tropical and subtropical ecosystems in South America could support 40% of these yet-to-be-identified species, they said.

“This study reminds us how little we know about our own planet and its biosphere,” said study co-author Jingjing Liang, professor of quantitative forest ecology at Purdue University in Indiana. “We still have so much more to learn about the Earth so we can better protect it and preserve natural resources for future generations.”

(Reporting by Will Dunham, Editing by Rosalba O’Brien)

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