Tree treasure hunt: 9000 species still to be discovered

Our planet is home to 9000 undiscovered tree species, according to the first-ever estimate of global tree biodiversity.

The new study, published in the journal PNAS, reflects the work of 150 scientists who have spent years identifying trees all over the world.

“It’s hugely exciting,” says Andy Marshall, a professor at the University of the Sunshine Coast who helped collect data in East Africa and Australia.

“This new global dataset is a significant piece of the puzzle in ecology and biodiversity. It’s based on the identification of trees growing in millions of vegetation plots around the world.”

Detailed knowledge of tree biodiversity is key to preserving stable and functional ecosystems, but until now, we had no global perspective – just local field observations and lists of species across different areas.

A few years ago this changed, when US forest ecologist Jingjing Liang founded the Global Forest Biodiversity Initiative (GFBI).

“I literally found a rich forest inventory dataset in someone’s drawer,” says Liang, who is now a professor at Purdue University. “I realised people would want that information, but it had never been published. Scientists would share their data on a project or request basis, but there was no central repository for the valuable data people were collecting.”

So he began collecting, and over the years data came in from all around the world.

“We combined individual datasets into one massive global dataset of tree-level data,” he explains. “Each set comes from someone going out to a forest stand and measuring every single tree – collecting information about the tree species, sizes and other characteristics.

“Counting the number of tree species worldwide is like a puzzle with pieces spreading all over the world. We solved it together as a team, each sharing our own piece.”

Now, their global dataset is the largest known to date – with 38 million individual trees logged from over 90 countries and 150 scientists.

“Through this vast amount of data, we have a good picture of tree species diversity for different biomes and at the continental level, which is what we used to make this estimate,” says Liang.

He also co-directs Purdue’s Lab of Forest Advanced Computing and Artificial Intelligence (FACAI), which was used to assess the massive dataset. Combining the power of FACAI’s supercomputer with AI, Liang and team performed statistical analyses to estimate the total number of unique tree species currently in existence on the planet.

The number they came up with – as reported in this new study – is 73,300.

64,100 of these have been confirmed by observations, which means that means there are 9200 yet to find.

The team thinks that about one-third of these are rare, with only a small number of individuals, and will likely be found in tropical or sub-tropical areas.

The study also suggests that about 40% of undiscovered tree species reside in South America, which already contains 43% of the planet’s tree species and the highest number of rare ones.

In addition, about 1500 undiscovered tree species are thought to exist in Oceania, most probably in the tropical and subtropical moist forests of northeast Australia and the Pacific Islands.

This highlights the vulnerability of forest biodiversity – as many undiscovered species are likely to be located in areas disproportionately threatened by climate change or land-use changes.

“It is very possible we could lose undiscovered tree species to extinction before we even find them,” Liang says.

But this study is one way to help.

Marshall explains that estimating the total number of tree species not only shows us how many exist across different ecosystems, but can also help us gauge their health.

“The better the information, the better we can inform national and international plans for conservation priorities and biodiversity targets and management – potentially saving endangered tree species in the process,” he says.