Number of Earth's tree species estimated to be 14% higher than currently known, with some 9,200 species yet to be discovered

Date:
January 31, 2022
Source:
University of Michigan
Summary:
A new study involving more than 100 scientists from across the
globe and the largest forest database yet assembled estimates
that there are about 73,000 tree species on Earth, including about
9,200 species yet to be discovered.



FULL STORY ==========================================================================
A new study involving more than 100 scientists from across the globe
and the largest forest database yet assembled estimates that there are
about 73,000 tree species on Earth, including about 9,200 species yet
to be discovered.


==========================================================================
The global estimate is about 14% higher than the current number of known
tree species. Most of the undiscovered species are likely to be rare, with
very low populations and limited spatial distribution, the study shows.

That makes the undiscovered species especially vulnerable to human-caused disruptions such as deforestation and climate change, according to the
study authors, who say the new findings will help prioritize forest conservation efforts.

"These results highlight the vulnerability of global forest biodiversity
to anthropogenic changes, particularly land use and climate, because
the survival of rare taxa is disproportionately threatened by these
pressures," said University of Michigan forest ecologist Peter Reich,
one of two senior authors of a paper scheduled for publication Jan. 31
in Proceedings of the National Academy of Sciences.

"By establishing a quantitative benchmark, this study could contribute
to tree and forest conservation efforts and the future discovery of new
trees and associated species in certain parts of the world," said Reich, director of the Institute for Global Change Biology at U-M's School for Environment and Sustainability.

For the study, the researchers combined tree abundance and occurrence
data from two global datasets -- one from the Global Forest Biodiversity Initiative and the other from TREECHANGE -- that use ground-sourced
forest-plot data. The combined databases yielded a total of 64,100
documented tree species worldwide, a total similar to a previous study
that found about 60,000 tree species on the planet.



==========================================================================
"We combined individual datasets into one massive global dataset of
tree-level data," said the study's other senior author, Jingjing Liang
of Purdue University, coordinator of the Global Forest Biodiversity
Initiative.

"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 spread all over the world."
After combining the datasets, the researchers used novel statistical
methods to estimate the total number of unique tree species at biome, continental and global scales -- including species yet to be discovered
and described by scientists. A biome is a major ecological community type,
such as a tropical rainforest, a boreal forest or a savanna.

Their conservative estimate of the total number of tree species on Earth
is 73,274, which means there are likely about 9,200 tree species yet to be discovered, according to the researchers, who say their new study uses a
vastly more extensive dataset and more advanced statistical methods than previous attempts to estimate the planet's tree diversity. The researchers
used modern developments of techniques first devised by mathematician
Alan Turing during World War II to crack Nazi code, Reich said.

Roughly 40% of the undiscovered tree species -- more than on any other continent -- are likely to be in South America, which is mentioned
repeatedly in the study as being of special significance for global
tree diversity.



========================================================================== South America is also the continent with the highest estimated number
of rare tree species (about 8,200) and the highest estimated percentage
(49%) of continentally endemic tree species -- meaning species found
only on that continent.

Hot spots of undiscovered South American tree species likely include
the tropical and subtropical moist forests of the Amazon basin, as well
as Andean forests at elevations between 1,000 meters (about 3,300 feet)
and 3,500 meters (about 11,480 feet).

"Beyond the 27,000 known tree species in South America, there might be
as many as another 4,000 species yet to be discovered there. Most of
them could be endemic and located in diversity hot spots of the Amazon
basin and the Andes- Amazon interface," said Reich, who was recruited
by U-M's Biosciences Initiative and joined the faculty last fall from
the University of Minnesota, where he maintains a dual appointment.

"This makes forest conservation of paramount priority in South
America, especially considering the current tropical forest crisis from anthropogenic impacts such as deforestation, fires and climate change,"
he said.

Worldwide, roughly half to two-thirds of all already known tree
species occur in tropical and subtropical moist forests, which are both species-rich and poorly studied by scientists. Tropical and subtropical
dry forests likely hold high numbers of undiscovered tree species,
as well.

"Extensive knowledge of tree richness and diversity is key to preserving
the stability and functioning of ecosystems," said study lead author
Roberto Cazzolla Gatti of the University of Bologna in Italy.

Forests provide many "ecosystem services" to humanity for free. In
addition to supplying timber, fuelwood, fiber and other products,
forests clean the air, filter the water, and help control erosion
and flooding. They help preserve biodiversity, store climate-warming
carbon, and promote soil formation and nutrient cycling while offering recreational opportunities such as hiking, camping, fishing and hunting.

========================================================================== Story Source: Materials provided by University_of_Michigan. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Roberto Cazzolla Gatti et al. The number of tree species on
Earth. PNAS,
2022 DOI: 10.1073/pnas.2115329119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220131153239.htm

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