Image copyright BGCI Image caption Bhutan's national Tsenden tree, conserved through international efforts

There are 60,065 species of trees in the world, according to a comprehensive study of the world's plants.

Botanical Gardens Conservation International (BGCI) compiled the tree list by using data gathered from its network of 500 member organisations.

It hopes the list will be used as a tool to identify rare and threatened species in need of immediate action to prevent them becoming extinct.

Details of the study appear in the Journal of Sustainable Forestry.

Image copyright BGCI Image caption Seeds of the Karomia Gigas tree, the last six remaining were found in Tanzania

The data revealed that Brazil was the nation with the greatest number of tree species, home to 8,715 varieties.

Apart from the polar regions, which have no trees, the near-Arctic region of North America had the fewest number of species, with less than 1,400.

Another fact to emerge from the data was that more than half of the species (58%) were only found in one country, suggesting that they were vulnerable to potential threats, such as deforestation from extreme weather events or human activity.

About 300 species have been identified as critically endangered as they had fewer than 50 individuals remaining in the wild.

'Unique position'

BGCI secretary general Paul Smith said that it was not possible to accurately estimate the number of tree species in the world until now because the data has only just been digitised.

"We are in a unique position because we have 500 botanical institutions as members," he told BBC News.

Image copyright BGCI Image caption The critically endangered Mulanje cedar, Malawi's national tree

"A lot of the data is not readily available to the public. The digitisation of this data, in effect, is the culmination of centuries of work."

An important factor of the study is the geo-referencing of the tree species, which allow conservationists to locate individual species, Dr Smith explained.

"Getting location information, such as which countries do these these trees occur in, gives us key information for conservation purposes.

"That is hugely useful for us in prioritizing which ones we need to do conservation action on and which ones we need to do assessments to find out what their status is," he added.

On the edge

BGCI identified a species that was on the edge of extinction as a result of overharvesting. Karomia gigas is found in a remote part of Tanzania. At the end of 2016, a team of scientists found a single population of just six trees.

Image copyright Kyle Dexter Image caption The recent digitisation of data has allowed researchers, for the first time, to estimate the number of tree species on the planet

They recruited local people to guard the trees and to notify them when the trees produced seeds.

The plan is for the seeds to be propagated in Tanzanian botanical gardens, allowing the species to be re-introduced back into the wild at a later date.

BGCI said that it did not expect the number of trees on its GlobalTreeSearch list to remain static as about 2,000 plants were newly subscribed each year. It would be updating the list whenever a new species was named.

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