- NASA satellite observation of deforestation in the Mato Grosso state of Brazil. The transformation from forest to farm is evident by the paler square shaped areas under development.
- Fires and deforestation in the state of Rondônia.
- One consequence of forest clearing in the Amazon: thick smoke that hangs over the forest.
- Anthropogenic emission of greenhouse gases broken down by sector for the year 2000.
- Aerosols over the Amazon each September for four burning seasons (2005 through 2008). The aerosol scale (yellow to dark reddish-brown) indicates the relative amount of particles that absorb sunlight.
- Aerial roots of red mangrove on an Amazonian river.
The Amazon rainforest (Portuguese: Floresta
Amazônica or Amazônia; Spanish: Selva
Amazónica, Amazonía or usually Amazonia; French: Forêt
amazonienne; Dutch: Amazoneregenwoud), also known in English as Amazonia or the Amazon Jungle, is a moist broadleaf forest in
the Amazon biome that covers most of
the Amazon basin of South America.
This basin encompasses 7,000,000 square kilometres
(2,700,000 sq mi), of which 5,500,000 square kilometres
(2,100,000 sq mi) are covered by the rainforest. This region
includes territory belonging to nine nations. The majority of the forest is
contained within Brazil, with 60% of the
rainforest, followed by Peru with 13%, Colombia with 10%, and with minor
amounts in Venezuela, Ecuador, Bolivia, Guyana, Suriname and French
Guiana. States or departments in four nations
contain "Amazonas" in their names. The
Amazon represents over half of the planet's remaining rainforests,[1] and
comprises the largest and most biodiverse tract of tropical
rainforest in the world, with an estimated
390 billion individual trees divided into 16,000 species.
Etymology
The
name Amazon is said to arise
from a war Francisco
de Orellana fought with the Tapuyas and
other tribes. The women of the tribe fought alongside the men, as was their
custom. Orellana derived the name Amazonas from
the Amazons of Greek mythology,
described by Herodotus and Diodorus.
History
Natural
The
rainforest likely formed during the Eocene era. It appeared
following a global reduction of tropical temperatures when the Atlantic Ocean
had widened sufficiently to provide a warm, moist climate to the Amazon basin.
The rainforest has been in existence for at least 55 million years, and most
of the region remained free of savanna-type biomes at least until
the current ice
age, when the climate was drier and savanna more widespread.
Following
the Cretaceous–Paleogene
extinction event, the extinction of the dinosaurs and the
wetter climate may have allowed the tropical rainforest to spread out across
the continent. From 66–34 Mya, the rainforest
extended as far south as 45°. Climate
fluctuations during the last 34 million years have allowed savanna regions to
expand into the tropics. During the Oligocene, for example, the
rainforest spanned a relatively narrow band. It expanded again during
the Middle Miocene,
then retracted to a mostly inland formation at the last glacial maximum. However,
the rainforest still managed to thrive during these glacial periods, allowing
for the survival and evolution of a broad diversity of species.
During
the mid-Eocene,
it is believed that the drainage basin of the Amazon was split along the
middle of the continent by the Purus
Arch. Water on the eastern side flowed toward the Atlantic, while to the
west water flowed toward the Pacific across
the Amazonas Basin.
As the Andes Mountains
rose, however, a large basin was created that enclosed a lake; now known as
the Solimões
Basin. Within the last 5–10 million years, this accumulating water
broke through the Purus Arch, joining the easterly flow toward the Atlantic.
There
is evidence that there have been significant changes in Amazon
rainforest vegetation over
the last 21,000 years through the Last Glacial Maximum (LGM)
and subsequent deglaciation. Analyses of sediment deposits from Amazon basin
paleolakes and from the Amazon Fan indicate that rainfall in the basin during
the LGM was lower than for the present, and this was almost certainly
associated with reduced moist tropical vegetation cover in the
basin. There is debate, however, over how extensive this reduction was.
Some scientists argue that the rainforest was reduced to small, isolated refugia separated
by open forest and grassland; other scientists argue that the rainforest
remained largely intact but extended less far to the north, south, and east
than is seen today. This debate has proved difficult to resolve because
the practical limitations of working in the rainforest mean that data sampling
is biased away from the center of the Amazon basin, and both explanations are
reasonably well supported by the available data.
Sahara Desert dust windblown to the Amazon
More
than 56% of the dust fertilizing the Amazon rainforest comes from the Bodélé
depression in Northern Chad in the Sahara desert. The dust
contains phosphorus,
important for plant growth. The yearly Sahara dust replaces the equivalent
amount of phosphorus washed away yearly in Amazon soil from rains and
floods. Up to 50 million tonnes of Sahara dust per
year are blown across the Atlantic Ocean.
NASA's CALIPSO satellite has
measured the amount of dust transported by wind from the Sahara to the Amazon:
an average 182 million tons of dust are windblown out of the Sahara each year,
at 15 degrees west longitude, across 1,600 miles (2,600 km) over the Atlantic
Ocean (some dust falls into the Atlantic), then at 35 degrees West longitude
at the eastern coast of South America, 27.7 million tons (15%) of dust fall
over the Amazon basin, 132 million tons of dust remain in the air, 43 million
tons of dust are windblown and falls on the Caribbean Sea, past 75 degrees
west longitude.
CALIPSO
uses a laser range finder to scan the Earth's atmosphere for the vertical
distribution of dust and other aerosols. CALIPSO regularly tracks the
Sahara-Amazon dust plume. CALIPSO has measured variations in the dust amounts
transported— an 86 percent drop between the highest amount of dust transported
in 2007 and the lowest in 2011.
A
possibility causing the variation is the Sahel, a strip of semi-arid
land on the southern border of the Sahara. When rain amounts in the Sahel are
higher, the volume of dust is lower. The higher rainfall could make more
vegetation grow in the Sahel, leaving less sand exposed to winds to blow away.
Human activity
Based
on archaeological evidence
from an excavation at Caverna da Pedra
Pintada, human inhabitants first settled in the Amazon region at least
11,200 years ago. Subsequent development led to late-prehistoric
settlements along the periphery of the forest by AD 1250, which induced
alterations in the forest cover.
For a
long time, it was thought that the Amazon rainforest was only ever sparsely
populated, as it was impossible to sustain a large population through agriculture given
the poor soil. Archeologist Betty Meggers was
a prominent proponent of this idea, as described in her book Amazonia: Man and Culture in a Counterfeit Paradise.
She claimed that a population density of 0.2 inhabitants per square kilometre
(0.52/sq mi) is the maximum that can be sustained in the rainforest
through hunting, with agriculture needed to host a larger
population. However, recent anthropologicalfindings
have suggested that the region was actually densely populated. Some 5 million
people may have lived in the Amazon region in AD 1500, divided between dense
coastal settlements, such as that at Marajó, and inland
dwellers. By 1900 the population had fallen to 1 million and by the early
1980s it was less than 200,000.
The
first European to travel the length of the Amazon River was Francisco de
Orellana in 1542. The BBC's Unnatural Histories presents
evidence that Orellana, rather than exaggerating his claims as previously
thought, was correct in his observations that a complex civilization was
flourishing along the Amazon in the 1540s. It is believed that the
civilization was later devastated by the spread of diseases from Europe, such
as smallpox.
Since
the 1970s, numerous geoglyphs have
been discovered on deforested land dating between AD 1–1250, furthering claims
about Pre-Columbian civilizations. Ondemar
Dias is accredited with first discovering the geoglyphs in 1977 and Alceu
Ranzi with furthering their discovery after flying over Acre. The
BBC's Unnatural Histories presented
evidence that the Amazon rainforest, rather than being a pristine wilderness, has been
shaped by man for at least 11,000 years through practices such as forest gardening and terra
preta. Terra preta is found over large areas in the Amazon
forest; and is now widely accepted as a product of indigenous soil management.
The development of this fertile soil allowed agriculture and silviculture in the
previously hostile environment; meaning that large portions of the Amazon
rainforest are probably the result of centuries of human management, rather
than naturally occurring as has previously been supposed. In the region
of the Xingu tribe,
remains of some of these large settlements in the middle of the Amazon forest
were found in 2003 by Michael Heckenberger and colleagues of the University of
Florida. Among those were evidence of roads, bridges and large plazas.
Biodiversity
Wet
tropical forests are the most species-rich biome, and tropical forests in
the Americas are consistently more species rich than the wet forests in Africa
and Asia. As the largest tract of tropical rainforest in the Americas,
the Amazonian rainforests have unparalleled biodiversity. One in ten
known species in the world lives in the Amazon rainforest. This
constitutes the largest collection of living plants and animal species in the
world.
The
region is home to about 2.5 million insect species, tens of
thousands of plants, and some 2,000 birds and mammals. To date, at least
40,000 plant species, 2,200 fishes, 1,294
birds, 427 mammals, 428 amphibians, and 378 reptiles have been scientifically
classified in the region. One in five of all bird species are found in
the Amazon rainforest, and one in five of the fish species live in Amazonian
rivers and streams. Scientists have described between 96,660 and 128,843 invertebrate species
in Brazil alone.
The
biodiversity of plant species is the highest on Earth with one 2001 study
finding a quarter square kilometer (62 acres) of Ecuadorian rainforest
supports more than 1,100 tree species. A study in 1999 found one square
kilometer (247 acres) of Amazon rainforest can contain about 90,790 tonnes of
living plants. The average plant biomass is estimated at 356 ± 47
tonnes per hectare. To date, an estimated 438,000 species of plants of
economic and social interest have been registered in the region with many more
remaining to be discovered or catalogued. The total number of treespecies in the region is
estimated at 16,000.
The
green leaf area of plants and trees in the rainforest varies by about 25% as a
result of seasonal changes. Leaves expand during the dry season when sunlight
is at a maximum, then undergo abscission in the cloudy wet season. These
changes provide a balance of carbon between photosynthesis and respiration.
The
rainforest contains several species that can pose a hazard. Among the largest
predatory creatures are the black caiman, jaguar, cougar, and anaconda. In the
river, electric eels can
produce an electric shock that can stun or kill, while piranha are known to
bite and injure humans. Various species of poison dart frogs secrete lipophilic alkaloid toxins through
their flesh. There are also numerous parasites and disease vectors. Vampire bats dwell
in the rainforest and can spread the rabies virus. Malaria, yellow fever and Dengue fever can
also be contracted in the Amazon region.
Deforestation
Deforestation is
the conversion of forested areas to non-forested areas. The main sources of
deforestation in the Amazon are human settlement and development of the
land. Prior to the early 1960s, access to the forest's interior was
highly restricted, and the forest remained basically intact. Farms
established during the 1960s were based on crop cultivation and the slash and burn method.
However, the colonists were unable to manage their fields and the crops
because of the loss of soil fertility and
weed invasion. The soils in the Amazon are productive for just a short
period of time, so farmers are constantly moving to new areas and clearing
more land. These farming practices led to deforestation and caused
extensive environmental damage. Deforestation is considerable, and areas
cleared of forest are visible to the naked eye from outer space.
In the
1970s construction began on the Trans-Amazonian
highway. This highway represented a major threat to the Amazon
rainforest.Fortunately for the rainforest, the highway has not been completed,
hereby reducing the environmental damage.
Between
1991 and 2000, the total area of forest lost in the Amazon rose from 415,000
to 587,000 square kilometres (160,000 to 227,000 sq mi), with most
of the lost forest becoming pasture for cattle. Seventy percent of
formerly forested land in the Amazon, and 91% of land deforested since 1970,
is used for livestock pasture. Currently,
Brazil is the second-largest global producer of soybeans after the
United States. New research however, conducted by Leydimere Oliveira et al.,
has shown that the more rainforest is logged in the Amazon, the less
precipitation reaches the area and so the lower the yield per hectare becomes.
So despite the popular perception, there has been no economical advantage for
Brazil from logging rainforest zones and converting these to pastoral fields.
The
needs of soy farmers have been used to justify many of the controversial
transportation projects that are currently developing in the Amazon. The first
two highways successfully opened up the rainforest and led to increased
settlement and deforestation. The mean annual deforestation rate from 2000 to
2005 (22,392 km2 or
8,646 sq mi per year) was 18% higher than in the previous five years
(19,018 km2 or
7,343 sq mi per year). Although deforestation has declined
significantly in the Brazilian Amazon between 2004 and 2014, there has been an
increase to the present day.
Conservation and climate change
Environmentalists
are concerned about loss of biodiversity that will result from destruction of
the forest, and also about the release of the carbon contained within
the vegetation, which could accelerate global warming.
Amazonian evergreen forests account for about 10% of the world's terrestrial
primary productivity and 10% of the carbon stores in ecosystems—of the order
of 1.1 × 1011 metric
tonnes of carbon. Amazonian forests are estimated to have accumulated
0.62 ± 0.37 tons of carbon per hectare per year between 1975 and
1996.
One computer model of
future climate
change caused by greenhouse gas emissions
shows that the Amazon rainforest could become unsustainable under conditions
of severely reduced rainfall and increased temperatures, leading to an almost
complete loss of rainforest cover in the basin by 2100. However,
simulations of Amazon basin climate change across many different models are
not consistent in their estimation of any rainfall response, ranging from weak
increases to strong decreases. The result indicates that the rainforest
could be threatened though the 21st century by climate change in addition to
deforestation.
In
1989, environmentalist C.M. Peters and two colleagues stated there is economic
as well as biological incentive to protecting the rainforest. One hectare in
the Peruvian
Amazonhas been calculated to have a value of $6820 if intact forest is
sustainably harvested for fruits, latex, and timber; $1000 if clear-cut for
commercial timber (not sustainably harvested); or $148 if used as cattle
pasture.
As
indigenous territories continue to be destroyed by deforestation and ecocide, such as in the Peruvian Amazon indigenous peoples'
rainforest communities continue to disappear, while others, like the Urarina continue to
struggle to fight for their cultural survival and the fate of their forested
territories. Meanwhile, the relationship between non-human primates in the
subsistence and symbolism of indigenous lowland South American peoples has
gained increased attention, as have ethno-biology and community-based
conservation efforts.
From
2002 to 2006, the conserved land in the Amazon rainforest has almost tripled
and deforestation rates have dropped up to 60%. About 1,000,000 square
kilometres (250,000,000 acres) have been put onto some sort of conservation,
which adds up to a current amount of 1,730,000 square kilometres (430,000,000
acres).
A 2009
study found that a 4 °C rise in global temperatures by 2100 would kill
85% of the Amazon rainforest while a temperature rise of 3 °C would kill
some 75% of the Amazon.
Remote sensing
The
use of remotely
sensed data is dramatically improving conservationists' knowledge of
the Amazon basin. Given the objectivity and lowered costs of satellite-based
land cover analysis, it appears likely that remote sensing technology will be
an integral part of assessing the extent and damage of deforestation in the
basin. Furthermore, remote sensing is the best and perhaps only possible
way to study the Amazon on a large-scale.
The
use of remote sensing for the conservation of the Amazon is also being used by
the indigenous tribes of the basin to protect their tribal lands from
commercial interests. Using handheld GPS devices
and programs like Google
Earth, members of the Trio Tribe, who live in the rainforests of southern
Suriname, map out their ancestral lands to help strengthen their territorial
claims. Currently, most tribes in the Amazon do not have clearly defined
boundaries, making it easier for commercial ventures to target their
territories.
To
accurately map the Amazon's biomass and subsequent carbon related emissions,
the classification of tree growth stages within different parts of the forest
is crucial. In 2006 Tatiana Kuplich organized the trees of the Amazon into
four categories: (1) mature forest, (2) regenerating forest [less than three
years], (3) regenerating forest [between three and five years of regrowth],
and (4) regenerating forest [eleven to eighteen years of continued
development]. The researcher used a combination of Synthetic
aperture radar (SAR) and Thematic Mapper (TM)
to accurately place the different portions of the Amazon into one of the four
classifications.
Impact of early 21st-century Amazon droughts
In
2005, parts of the Amazon basin experienced the worst drought in one hundred
years, and there were indications that 2006 could have been a second
successive year of drought. A July 23, 2006 article in the UK
newspaper The Independent reported Woods Hole
Research Center results showing that the forest in its present form
could survive only three years of drought. Scientists at the
Brazilian National
Institute of Amazonian Research argue in the article that this
drought response, coupled with the effects of deforestation on regional
climate, are pushing the rainforest towards a "tipping point"
where it would irreversibly start to die. It concludes that the forest is on
the brink of being turned into savanna or desert, with catastrophic
consequences for the world's climate.
According
to the World
Wide Fund for Nature, the combination of climate change and deforestation
increases the drying effect of dead trees that fuels forest fires.
In
2010 the Amazon rainforest experienced another severe drought, in some ways
more extreme than the 2005 drought. The affected region was approximate
1,160,000 square miles (3,000,000 km2)
of rainforest, compared to 734,000 square miles (1,900,000 km2) in 2005. The 2010 drought had three
epicenters where vegetation died off, whereas in 2005 the drought was focused
on the southwestern part. The findings were published in the journal Science.
In a typical year the Amazon absorbs 1.5 gigatons of carbon dioxide; during
2005 instead 5 gigatons were released and in 2010 8 gigatons were
released. Additional severe droughts occurred in 2010, 2015, and 2016.