Western Sydney University researchers have contributed to a world-first study that estimates there are 73,000 tree species on Earth, including about 9,200 species yet to be discovered, of which 1,500 species are likely to be concentrated in northeast Australia and the Pacific Islands.
The team of 100 scientists worked collaboratively on an extensive global forest database to calculate the estimate, and believe the number of species identified is about 14 per cent higher than the current number of known tree species.
The study, published in the Proceedings of the National Academy of Sciences (PNAS), also suggests most of the undiscovered species are likely to be rare and vulnerable.
Research co-author tree physiologist Associate Professor Sebastian Pfautsch, from the University's School of Social Sciences, said the study offered a unique global perspective that had not been achieved before.
"Due to data limitations, it has previously been very challenging to get an accurate understanding of how many tree species are in the world," said Associate Professor Pfautsch.
"Findings from our global database represent years and years of collective research efforts, and the resulting estimate will help us prioritise conservation efforts, such as identifying and protecting new species.
"In Oceania, we anticipate new species are located in tropical and subtropical moist forests, including those in northeast Australia."
As part of the study, 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.
Almost one-third of all tree species to be discovered may be rare, with very low populations and limited spatial distribution (likely in remote tropical lowlands and mountains), with the largest portion of undiscovered tree species in South America, followed by North America, Eurasia, Oceania and Africa.
Co-lead author forest ecologist Professor Peter Reich, who is affiliated with Western Sydney University's Hawkesbury Institute for the Environment as well as the Universities of Minnesota and Michigan, said the study would provide a benchmark for future conservation efforts.
"The findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species, and thus global tree richness," said Professor Reich.
The authors state that losing regions of forest that contain rare species will have direct and potentially long-lasting impacts on the global species diversity and their provisioning of ecosystem services.
