A few tree species dominate diverse Amazon rain forest

18.10.2013 14:53

The Amazon is the largest and most
diverse rain forest in the world — about
10 percent of all known species on Earth
dwell there — but only a few dozen of the
Amazon's thousands of tree species rule
the jungle, researchers recently found.
This new analysis can help reveal which
Amazon tree species face the most severe
threats of extinction and which areas
there are most in need of protection,
scientists added.
Until now, researchers' knowledge of the
types of trees in the Amazon and where
they were located was based on analyses
of regions — the rain forest's vast
expanse made it challenging to survey in
its entirety. For instance, scientists didn't
even know the most common tree species
in the Amazon.
To help shed light on this giant rain
forest's tree composition, more than 120
scientists cataloged any trees with stems
thicker than 3.9 inches (10 centimeters)
at 1,170 different locations throughout
Amazonia, the 2.3-million-square-mile
area (6 million square kilometers)
surrounding the Amazon River . They
found that about 16,000 tree species
made up this region. [ Amazon Photos:
Trees That Dominate the Rain Forest]
'Hyperdominant' trees
Of these 16,000 tree species, scientists
unexpectedly discovered that only 227
species, or 1.4 percent of all the types of
trees in Amazonia, made up half of the
nearly 400 billion total trees estimated to
live there.
"That's a much smaller number than
anyone anticipated," study lead author
Hans ter Steege, a tropical forest ecologist
at the Naturalis Biodiversity Center in
Leiden, Netherlands, said in a statement.
Hardly any of these "hyperdominant"
species, as the researchers call them, are
consistently common across the Amazon.
Each usually specializes in certain habitats
— one or two types of forest, such as
swamps or white-sand forests.
It remains unclear what makes any given
species hyperdominant. One possibility is
that hyperdominant species are unusually
resistant to disease and herbivores.
"There's a really interesting debate
shaping up between people who think
that hyperdominant trees are common
because pre-1492 (i.e., pre-Christopher
Columbus) indigenous groups farmed
them and people who think those trees
were dominant long before modern
humans ever arrived in the Americas,"
study co-author Nigel Pitman, an ecologist
and conservationist of the Field Museum
in Chicago, said in a statement.
Incidentally, the most common tree
species in Amazonia is the palm species
Euterpe precatoria, a relative of the açaí
palm Euterpe oleracea), whose sweet
berries are growing in popularity
worldwide. The researchers estimate that
5.2 billion Euterpe precatoria live in
The scientists also estimated that 11,000
of Amazonia's tree species are very rare,
which each of these rare types composed
of fewer than 1 million trees and in total
accounting for just 0.12 percent of all
trees in Amazonia. Many of these tree
types run a high risk of becoming extinct,
even before biologists can discover them,
the researchers said.
Better protection
Now that scientists have a better idea of
where populations of tree species are
located there, they can figure out which
Amazonian tree species might face the
most severe threats of extinction.
"We can better predict the effect of
deforestation and protection on
populations of trees," ter Steege told
LiveScience's OurAmazingPlanet.
In addition, conservation groups "can
now better determine in which areas the
richest, most diverse and potentially
endangered species are found," Johan van
de Gronden, director of the World Wildlife
Fund Netherlands, said in a statement.
"For the future of the Amazon, this is of
great importance."
The scientists detail their findings in
Friday's issue of the journal Science.