An International team of scientists think they have the answer – about 73,000

Researchers also think that about 9,000 of the 73,000 estimated species are yet to be discovered and will need names and scientific descriptions.

According to the research, led by Roberto Cazzolla Gatti of Purdue University and the Global Forest Biodiversity Initiative, “these findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species and global tree richness.”

Almost 6,700 known tree species and 1,500 undiscovered species were estimated in Oceania, including Australia. The research found a ‘hot spot’ of likely undiscovered species in the tropical and subtropical moist forests of northeast Australia and the Pacific Islands.

The researchers estimate that one-third of the undiscovered species are rare with small numbers of trees and likely exist in tropical or subtropical areas like the Amazon Rain Forest.

 Jingjing Liang, Professor of quantitative forest ecology in Purdue’s Department of Forestry and Natural Resources,explained:

“South America contains roughly 43% of the planet’s tree species and the highest number of rare species. It is very possible we could lose undiscovered tree species to extinction before we even find them.”

The global initiative GFBI has steadily grown over the past five years, and its efforts to understand the world’s tree population are bearing fruit. The global tree species estimate follows development of the first global map of tree symbioses, published in the journal Nature, and discovery that forest biodiversity benefits the economy by more than five times the cost of conservation efforts, published in the journal Science.

Professor Andy  Marshall of the University of the Sunshine Coast Forest Research Institute  said that estimating the planet’s total number of tree species helped show how many different ecosystems existed and gauge the health of those systems.

“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 said.

He is continuing the tree identification research this year with PhD students from USC in Australia and Tanzania and with his charity, Reforest Africa.

“In Queensland, we’ll be working on setting up new vegetation plots from Cape York in the north to Lamington in the south, including the Sunshine Coast, to add to existing research plots across the Cassowary Coast and Atherton Tablelands,” he said.

Professor Marshall, who started researching trees in 1998 in Tanzania, said his recent highlights were discovering two new African tree species from the custard apple family.

“One of them, the Mischogyne iddi, is a flowering tree that grows up to 20 metres tall up in the mountains. We named it after a Tanzanian botanist. He was stoked!”

The study “ The number of tree species on Earth” is published in PNAS,  The Proceedings of the National Academy of Sciences of the United States of America

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