(CN) — An international team of scientists scoured the world’s largest forest database to determine how many species of trees exist on the planet. They found the number of unique species to be 14% higher than previous estimates, with many species being exceptionally rare and having a limited range.
Because of their limited geographic ranges, many of those tree species are considered especially vulnerable to human-induced disruptions such as deforestation, fires and climate change. Around 40% of all undiscovered tree species on Earth are predicted to be found in South America, more than any other continent, with one-third of those thought to be rare and likely found in tropical lowlands or mountainous regions.
The research team combed through records of a combined 64,100 documented tree species looking for insights, and published their results Monday in a new study in the journal PNAS. The authors hope these new findings will encourage forest conservation efforts where they’re needed most, and prevent further encroachment into vulnerable habitats where the rarest species dwell.
"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 Peter Reich, director of the Institute for Global Change Biology at University of Michigan’s School for Environment and Sustainability, and senior author of the study, in a related statement. "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.”
The authors searched two global datasets, one from the Global Forest Biodiversity Initiative and another from the group TREECHANGE — both of which rely on ground-sourced forest-plot data for their numbers. By applying novel statistical techniques, they determined 73,274 tree species currently exist on Earth, 9,200 of which remain undiscovered.
To arrive at that number, the team compared species accumulation curves, which measures the cumulative number of species living in a particular environment as a function of the effort spent looking for them. That allowed the team to determine the number of species that remain unrecorded in the dataset.
"We combined individual datasets into one massive global dataset of tree-level data," said Jingjing Liang, coordinator of the Global Forest Biodiversity Initiative, and the study's other senior author, in a related statement. "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."
The highest estimated number of tree species across every continent were found in the tropical and subtropical moist forest biomes; between half to two-thirds of all known species occur in these continental forests. Tropical and subtropical dry forests, temperate forests, mangrove forests and non-forested biomes also contain significant numbers of known and unknown tree species. However, most forests remain dominated by just a few primary types.
Unsurprisingly, the two continents estimated to share the greatest number of tree species is North America and South America, which are connected by land in a region where species-rich tropical forests occur on both sides. The second-highest number of shared tree species occurs in Eurasia and Oceania due to their geological continuity through the Southeast Asian archipelago, which itself contains a tremendous amount of tree-species diversity.
The authors suggest that more conservation efforts should be prioritized in South America because of the region’s abundant tree species, particularly those that are rare and vulnerable to encroachment by humans. Tropical and subtropical forests of the Amazon basin should be a particular focus, along with Andean forests between the elevations of 3,300 feet and 11,480 feet, according to the study.
“This study reminds us how little we know about our own planet and its biosphere,” concluded Liang in an email. “There is so much more we need to learn about the Earth, so that we can better protect it, and conserve natural resources for future generations.”
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