The Amazon's Black Box

October 22, 2013

The Amazon rainforest is home to the world’s greatest plant diversity.  But the vast extent and inaccessibility of Amazonian forests have, until recently, prevented scientists from answering one of the simplest questions about the Amazon – how many trees are out there?

Now scientists in the Field Museum's rapid inventory team, together with over a hundred other experts on the Amazon, have answered that question: There are almost half a trillion individual trees in the greater Amazon – close to the number of stars in the Milky Way - and those trees belong to an estimated 16,000 species!

Most exciting of all is the discovery that half of all trees in the Amazon belong to just 227 species – a tiny 1.4% of the total diversity – that scientists have termed “hyperdominants”.

The study also found that an estimated 6,000 Amazonian tree species have populations of fewer than 1,000 individuals, which automatically qualifies them for inclusion in the IUCN Red List of Threatened Species.  The catch, say the authors, is that these species are so rare that scientists may never find them.

The Amazon has been called a “black box” for this reason – a forest whose overwhelming scale and diversity hamper efforts to describe its contents.  Ecologist Miles Silman of Wake Forest University has another term for the thousands of rare tropical species that may never be found: “dark biodiversity”.

Silman’s term alludes to “dark matter” – the stuff that physicists believe makes up most of our universe, but have never seen.  “Our models tell us that species too rare to find account for much of the planet's biodiversity,” says Silman.  “That's a real problem for conservation, because the species at the greatest risk of extinction may disappear before we ever find them."

While scientists are confident that these hyperdominants also dominate the country-sized expanses of Amazonia where scientists have yet to carry out tree surveys, they do not know why some species are hyperdominant and others are rare.

Field Museum botanists are hard at work on those questions today, and the Museum has been a leader in Amazonian plant research for nearly 90 years. With the fifth-largest herbarium in the Western Hemisphere, the Museum maintains one of the world's largest collections of Amazonian plant specimens – which includes most of the hyperdominants.  See some of them up close, on display now at The Field Museum.

Explore more about The Field Museum's work in the Andes-Amazon region.