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Just 227 tree species dominate Amazon

Researchers were surprised to find that such a small proportion of species dominated the Amazon .
Despite being home to about 16,000 tree species, just 227 "hyperdominant" species account for half of Amazonia's total trees, a study suggests.

An international team of researchers found that the region was, in total, home to an estimated 390 billion trees.

Writing in Science, they added that the rarest 11,000 species made up only 0.12% of tree cover.

However, they added that the new data could help unlock ecological secrets held by the biodiversity hotspot.

The results were based on a survey of 1,170 plots and half-a-million trees across the six-million-square-kilometre area, often described as the lungs of the world.

The authors said that the underlying cause of the hyper dominance of the 227 species, which accounted for 1.4% of the estimated number of species in the region, remained unknown.

"We knew that, normally, a few species dominate ecosystems, but if you have a system that has 16,000 tree species but just 227 make up half of the trees, that was pretty surprising even for us," said lead author Dr Hans ter Steege from the Naturalis Biodiversity Center in the Netherlands.

He told the Science podcast: "We don't really know why these species are so incredibly dominant because they do not have any particular ecological feature that stands out."

In the paper, Dr ter Steege and the team of more than 100 scientists wrote that there was no evidence that two key functional traits for trees - seed mass and wood density - played a part in determining what species dominated the landscape.

"The 227 hyperdominant species include both shade-tolerant, typically large-seeded climax species with dense wood and shade-intolerant, small seeded pioneer (species) with light wood," they observed.

The most dominant species was indentified as Euterpe precatoria, a palm tree native to central and southern America, with a mean estimate population of more than five billion individuals within Amazonia.

Conversely, the researchers noted that the rarest 5,800 species had communities with fewer than 1,000 individuals, adding: "which is sufficient to classify those that are endemic as globally threatened".

They suggested further analysis would show that the species identified as hyperdominant would be "disproportionately resistant to pathogens, specialist herbivores and other sources of frequency-dependent mortality".

Dr ter Steege said the data could also be used by conservationists to find out what species were found in protected areas, such as national parks, and what ones were located in unprotected areas, and were therefore vulnerable to threat such as deforestation.