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How many kinds of trees are there?

A recent study found that there are an estimated 73,000 tree species currently living in the world.
Cristy Meiners
A recent study found that there are an estimated 73,000 tree species currently living in the world.

On a road trip last week, I counted the number of different types of cars that whizzed by, responding to that human urge to tally the diversity around us.

I came up with 42 models, a tiny fraction of the many cars manufactured over the years.

As a tree lover, of course I then wondered: How many different types of trees are there? A recent scientific paper — co-authored by 143 authors from 62 countries — gave me the answer.

Based on an exhaustive inventory of 5 million trees in 100,000 forest plots, their estimate was …. over 73,000 tree species. And that’s just the number of species living today. It doesn't include those that have gone extinct since trees evolved, 380 million years ago.

Not surprisingly, tree diversity is highest in the tropics, where life has evolved without the glacial interruptions that polar and temperate regions have experienced over geologic time. And South America is the champion continent for tree diversity, hosting a whopping 43% of the world’s estimated tree species.

Based on their statistical analyses, the authors also suggested that there are another 9,000 species yet to be discovered, many of which they predict will be extremely rare, and thus vulnerable to human changes in land use and climate.

Why did these 143 scientists invest years in tallying tree species? Well, just as automobile dealers need accurate inventories of their cars to avoid running out of the models their customers want, so does this tree species inventory serve as a step to guide protection of trees and the resources they provide for animals, plants, water, air, soil — and people.

Dr. Nalini Nadkarni is an emeritus professor of both The Evergreen State College and the University of Utah, one of the world’s leading ecologists and a popular science communicator. Dr. Nadkarni’s research and public engagement work is supported by the National Geographic Society and the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. @nalininadkarni
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