More than 9 000 tree species yet to be d iscovered

A NEW study involving more than 100 scientists from across the globe and the largest forest database yet has assembled astonishing estimates of there being 73 000 tree species on the Earth, including about 9 200 species yet to be discovered.

The study was published in Proceedings of the National Academy of Sciences.

The global estimate was 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 showed.

This made the undiscovered species especially vulnerable to human-caused disruptions such as deforestation and climate change, according to the study authors, who said, the new findings will help prioritise 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 (UM) forest ecologist Peter Reich, one of two senior authors of the study.

“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 UM’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, co-ordinator 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,” said Jingjing.

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 was 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 included the tropical and subtropical moist forests of the Amazon basin, as well as Andean forests at elevations between 1 000 and 3 500 metres.