Naturalists and botanist have spent countless years in the Amazon rainforest cataloging every tree, vine, orchid and scrap of moss they could find. But after over three centuries of almost continuous exploration, there’s one problem: no one kept a master list of all the tree species.
That’s why a new project led by Hans ter Steege of the Naturalis Biodiversity Center in the Netherlands recently tallied up all the species he and his team could find. The final count was recently published in the journal Scientific Reports.
“Before this paper we didn’t have a list of Amazonian trees,” co-author Nigel Pitman, a tropical forest ecologist at the Field Museum in Chicago tells Nicholas St. Fleur at The New York Times. “With this list we are answering ‘How many species have been found?’ and ‘What are they?’”
The team looked at more than half a million digitized specimens from collections around the world collected between 1707 and 2015, coming up with 11,676 species of Amazon trees in 1,225 genera and 140 families.
Pitman admits the checklist isn’t as accurate or meticulous as one that would be constructed by a formal taxonomist. But he says the team hopes it will be a jumping off point for the scientific community who can amend and refine it. “What cracks me up about this paper is that it’s a bunch of ecologists who got impatient and said ‘Let’s see if we can make a quick checklist and see what we get,’” he tells Le Fleur. “This is an effort to pull together this 300-year-long research on this incredibly diverse region and convert it into a simple tool that anybody can use.”
The tally wasn’t completely unexpected. In 2013 Steege conducted another study, looking at 1,170 Amazon forestry surveys. Based on that data, he estimated the Amazon basin holds 16,000 tree species and about 390 billion individual trees. Half of those trees, however come from just 227 hyperdominant species. About 6,000 of those species have only 1,000 individuals or less, which would automatically place them on the endangered list—that is, if researchers could locate them. It's a phenomenon Wake Forest researcher Miles Silman dubs “dark bioversity.”
“Just like physicists’ models tell them that dark matter accounts for much of the universe, our models tell us that species too rare to find account for much of the planet’s biodiversity,” Silman says in a press release. “That’s a real problem for conservation, because the species at the greatest risk of extinction may disappear before we ever find them.”
Several researchers criticized that original paper, estimating that the Amazon only held roughly 6,000-7,000 total species. “We interpret this [new paper] to mean that our 2013 estimate of 16,000 species is good, and that about 4,000 of the rarest Amazonian trees remain to be discovered and described,” Pitman says in the press release.
Some of those missing trees may eventually show up in forgotten botanical collections or at institutions that have not yet digitized their specimens. Many are probably hiding among the rainforests billions of trees. Pitman points out that since 1900, botanists have discovered 50 to 200 new trees per year in the Amazon. It may take centuries, he said, to eventually find them all.