研究：世界上仍有许多未知的树木

From Peru to Australia, Madagascar to California, the world has many wonderful tree species. How many? A new study suggests there are about 73,000 kinds of trees, many of them still undiscovered. Such information reminds us of how much more we can learn about the Earth, experts say.

Largest forest database

Researchers recently revealed the world's largest forest database, one that is made up of more than 44 million trees at more than 100,000 locations in 90 countries.

Researchers used the data to estimate that Earth has about 73,300 tree species.

That number is about 14 percent higher than earlier estimates. Of that total, about 9,200 are estimated to exist based on mathematical predictions but have not yet been identified by science. Many of these trees grow in South America, the researchers said.

South America, home to the Amazon rainforest and Andean forests, was found to have 43 percent of the planet's tree species and the largest number of rare species, at about 8,200.

Roberto Cazzolla Gatti of the University of Bologna in Italy was the lead writer of the study that appeared recently in the publication Proceedings of the National Academy of Sciences.

Trees and forests are much more than just oxygen producers, Gatti said, explaining that they play an important part in the health of the environment.

He added, "Our society often considers forests as just pieces of wood and trees as natural resources... From trees and forests humanity gets inspiration, relaxation, spirituality and essentially the meaning of life."

The research team estimated that South America has about 27,000 known tree species and 4,000 yet to be identified.

The team also had estimates for other areas of the world.

Europe and Asia have about 14,000 known species and 2,000 unknown species.

Africa has 10,000 known species and 1,000 unknown; North America including Central America has 9,000 known and 2,000 unknown; while Oceania including Australia has 7,000 known and 2,000 unknown.

Importance of the study

study co-writer Peter Reich of the University of Michigan and University of Minnesota said that by measuring the number of trees "our study can contribute to tree and forest conservation efforts."

Conservation is a term that means the protection of plants, animals, and the natural environment.

Reich believes that "tree species diversity is key to maintaining healthy, productive forests, and important to the global economy and to nature."

He added that the information in the study "is important because tree species are going extinct due to deforestation and climate change, and understanding the value of that diversity requires us to know what is there in the first place before we lose it."

This study did not estimate the total number of individual trees globally. But 2015 research led by one of the co-authors put that number at about 3 trillion.

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

The researchers used methods developed by mathematicians to estimate the number of unknown species by using the numbers of known species. Tropical and subtropical areas in South America may have 40 percent of these yet-to-be-identified species, they said.

Jingjing Liang of Purdue University in Indiana was a co-writer of the study.

"This study reminds us how little we know about our own planet ....there is so much more we need to learn about the Earth so that we can better protect it and conserve natural resources for future generations," Liang said.

I'm John Russell.

Will Dunham reported on this story for Reuters. John Russell adapted it for Learning English.

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species – n. biology : a group of animals or plants that are similar and can produce young animals or plants : a group of related animals or plants that is smaller than a genus

inspiration—n. something that makes someone want to do something or that gives someone an idea about what to do or create : a force or influence that inspires someone

relaxation – n. a way to rest and enjoy yourself

deforestation -- n. the act or result of cutting down or burning all the trees in an area