Tree diversity is fundamental for forest ecosystem stability and services. However, because of limited available data, estimates of tree diversity at large geographic domains still rely heavily on published lists of species descriptions that are geographically uneven in coverage. Based on global ground-sourced data, a multinational team of scientists has estimated the total tree species richness at global, continental, and biome levels. Their results indicate that there are 73,274 tree species globally, among which about 9,200 tree species are yet to be discovered.
“It’s hugely exciting. This new global dataset is a significant piece of the puzzle in ecology and biodiversity,” said Professor Andy Marshall, a researcher with the Coast Forest Research Institute at the University of the Sunshine and the Department of Environment and Geography at the University of York.
“It’s based on the identification of trees growing in millions of vegetation plots around the world.”
“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,” added Dr. Peter Reich, a forest ecologist with the Institute for Global Change Biology and School for Environment and Sustainability at the University of Michigan, the Department of Forest Resources at the University of Minnesota, St. Paul, and the Hawkesbury Institute for the Environment at Western Sydney University.
“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.”
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.
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.
“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,” said Dr. Roberto Cazzolla Gatti, a researcher with Purdue University and the Global Forest Biodiversity Initiative.
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 m (about 3,300 feet) and 3,500 m (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,” Dr. Reich said.
“Most of them could be endemic and located in diversity hot spots of the Amazon basin and the Andes-Amazon interface.”
“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.”
The results appear in the Proceedings of the National Academy of Sciences.
Roberto Cazzolla Gatti et al. 2022. The number of tree species on Earth. PNAS 119 (6): e2115329119; doi: 10.1073/pnas.2115329119
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