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Map showing world distribution of rainforests
Section 1:
BIOGEOGRAPHICAL TROPICAL FOREST REALMS
Most "tropical rainforest", 2005. These rankings are estimates.
1
Brazil
2
Congo, Dem Rep
3
Peru
4
Indonesia
5
Colombia
6
Papua New Guinea
7
Venezuela
8
Bolivia
9
Mexico
10
Suriname
11
Guyana
12
Madagascar
13
French Guiana
14
Congo
15
Ecuador
16
Thailand
17
Malaysia
18
Panama
19
Guatemala
20
Nicaragua
21
Honduras
22
Laos
23
Philippines
24
Côte d'Ivoire
25
Belize
The majority of tropical rainforests
are found in four biogeographic realms: the Afrotropical (mainland Africa,
Madagascar, and scattered islands), the Australian (Australia, New Guinea,
and the Pacific Islands), the Indomalayan (India, Sri Lanka, mainland
Asia, and Southeast Asia), and the Neotropical (South America, Central
America, and the Caribbean islands).
Most of the tropical rainforests of Africa exist in the Congo (Zaire)
River Basin, although an unbroken forest once stretched from Senegal
on the Atlantic coast to the Rift Valley. West Africa has suffered heavy
deforestation from logging and agriculture and only a small portion
of the original cover remains. Timber from Central Africa, especially
Gabon, Cameroon, and the Congos, is increasingly used to fill the void
created by the departure from the market of West African timber exporters.
Consequently, deforestation is accelerating in Central Africa, at the
fastest rate of any realm during the 1980s and early 1990s. Overall
Africa had the highest deforestation rate of any biogeographical realm
for the periods from 1980-1990, 1990-2000, and 2000-2005.
Around the turn of the century, West Africa had some 193,000 sq. miles
(500,000 sq. km) of coastal rainforest. However, the tropical forests
of West Africa, mostly lowland formations easily accessible from the
coast, have been largely depleted by commercial exploitation, namely
logging, and conversion for agriculture. Now, according to the Food
and Agriculture Organization of the United Nations, less than 20 percent
of West Africa's moist forests remain, of which much is degraded. In
more populous states, notably Nigeria, human population pressures have
put a tremendous strain on forests, while other countries
like Côte d'Ivoire have suffered extensive forest loss as
a result of commercial logging and agriculture. The effects from forest
loss are yet to be fully understood, though erosion has greatly increased
as has the incidence of drought in the interior countries of Mali and
Niger. These coastal forests appear to play a substantial role in maintaining
rainfall in these interior countries.
The rainforests of Central Africa still cover a substantial area, although
this is rapidly declining. 75 percent of Africa's remaining
rainforest is located in Central Africa, covering about 540,000 square
miles (1.4 million square km). The bulk of this region's remaining forests
are found in the Congo Basin in the Democratic Republic of Congo and
Congo. These forests are mostly threatened by logging and subsistence
activities, especially fuelwood collection and agriculture.
The bulk of the forest
in this region lies on the world's second largest island, New Guinea.
Australia has small sections of forest on the Cape York peninsula in
the extreme northeastern part of the continent near the coast.
New evidence suggests that Australian rainforest covers more of Australia
today than it did in the past 18,000 years. Under the cooler and drier
conditions (rainfall decreased by as much as 80 percent) of
the past glacial period, Australia's rainforest retreated and was replaced by dry, fire-loving eucalyptus. When the ice ages ended,
small pockets of rainforest (10-20 percent of the coverage
that exists today) that survived served as refuges to recolonize the
surrounding land.
The plant and animal species of New Guinea and Australia, including
the original Australoid dark-skinned, frizzy-haired human
inhabitants, are similar because during the ice ages, when
the sea levels dropped, these two land bodies were linked. As a result,
both land masses have an unusually high diversity of marsupials which
have filled the niches left vacant by the absence of cats, monkeys,
civets, and other mammal groups. Also part of the ancient land mass
were the Aru islands, a group of small closely-packed islands
of the western coast of New Guinea. The strip of water between these
Aru islands and the Kei islands to the west, is the dividing line between
the Australian realm and the set of islands connected to neither realm
during the recent ice ages. These islands, including Lombock, Flores,
Timor, Sulawesi (Celebes), Ceram, Halmahera, are today part of Indonesia
and house their own unique species, many of which are characteristic
of neither the Indomalayan nor Australian realm. On Sulawesi (Celebes),
when bats are excluded, mammal endemism is 100 percent, meaning none of the island's mammal species are found elsewhere.
Although technically not part of any realm, oceanic Pacific Islands
will be mentioned here. These islands, many of which are volcanic, have
never been part of a mainland mass. These islands also have forest cover,
although these forests only make up a tiny portion of the world's total.
The majority of the remaining
tropical rainforest in Asia lies in Indonesia (on scattered islands),
the Malay peninsula (Malaysia, Thailand, Myanmar), and Laos and Cambodia.
Forest once covered a much greater area in Asia, but centuries of tremendous
population pressure has significantly reduced the natural extent, and
today only scattered fragments remain.
Southeast Asia's rainforests are some of the oldest on Earth. Studies
suggest that some forests in present day Malaysia may have existed over
100 million years ago. However, these ancient forests did not much resemble
the ones of today. These early rainforests had far fewer flowering plants,
so species today associated with flowering plants, including
many birds, insects, and mammals, had yet to come into existence. Borneo,
Sumatra, Java, and other Southeast Asian islands lacked many of the
familiar large mammals they have today. When the ice ages caused a drop
in sea level these animals migrated from greater Asia to Southeast Asia.
Ice ages lock up ocean waters in polar ice and cause ocean waters to
condense, causing the existing sea levels to fall. These events meant
profound changes for Southeast Asia since much of the shallow South
China Sea became dry land. As the ocean levels dropped, Sumatra, Java,
Borneo, the Malay Peninsula, and Indochina were connected,
allowing mainland and island species to cross over. As global
temperatures cooled and glaciation expanded, the tropical rainforest
retreated to small pockets and in many areas was replaced by deciduous
forest, savanna, or montane forest. The more extensive montane habitats
and savanna habitats enabled mountain and savanna plants and animals
like guar (a relative of the domestic cow) and the tiger to disperse into the tropics.
As the ice age ended, glaciers retreated, and the climate warmed, the
tropical rainforest surviving in Sumatra, Borneo, and Malay Peninsula
served as a reservoir from which species could recolonize surrounding
areas as they returned to forest. This could explain why today the pockets
of remaining montane forest like that of Mount Kinabalu in Sabah (Malaysian
Borneo) have flora that more closely resembles the plants of the Himalayas
and New Zealand.
The "Wallace line," named in honor of the nineteenth century biogeographer Alfred Wallace,
separates the Indomalayan realm from the Australian realm. Wallace first
documented the odd discontinuity of fauna between Bali and Lombock and
is credited, along with the renowned British naturalist Charles Darwin,
in formulating the theory of evolution. The Indomalayan realm
extends east to Borneo and south to Bali. Sulawesi (Celebes) and Lombock,
despite their proximity to Borneo and Java (respectively), are not included
because they are separated by a deep channel and were not linked to
the Indomalayan land mass formed when the ocean
receded during the ice ages. Land-based species,
and many flying species deterred by the winds, were not able to cross
over and the flora and fauna are quite different and distinct in these
adjacent areas.
The Amazon River Basin
is roughly the size of the forty-eight contiguous United States and
covers some 40 percent of the South American continent. Reflecting
environmental conditions as well as past human influence, the Amazon
is made up of a mosaic of ecosystems and vegetation types including
rainforests, seasonal forests, deciduous forests, flooded forests, and
savannas, among others. The basin is drained by the Amazon River, the
world's largest river in terms of discharge, and the second longest
river in the world after the Nile. The river is made up of over 1,100
tributaries, 17 of which are longer than 1000 miles, and two of which
(the Negro and the Madeira) are larger, in terms of volume, than the
Zaire river. The river system is the lifeline of the forest and its
history plays an important part in the development of its rainforests.
At one time Amazon River flowed westward, perhaps as part of a proto-Congo
(Zaire) river system from the interior of present day Africa when the
continents were joined as one as part of Gondwana. Fifteen million years
ago (an eye-blink in geologic time), the Andes were formed when they
were forced up by the collision of the South American plate with the
Nazca plate. The rise of the Andes and the linkage of the Brazilian
and Guyana bedrock shields blocked the river and caused the
Amazon to become a vast inland sea. Gradually this inland sea became
a massive swampy, freshwater lake and the marine inhabitants adapted
to life in freshwater. For example, over 20 species of stingray, most
closely related to those found in the Pacific Ocean, can be found today
in the freshwaters of the Amazon.
About ten million years ago, waters worked through the sandstone to
the west and the Amazon began to flow eastward. At this time the Amazon
rainforest was born. During the ice age, sea levels
dropped and the great Amazon lake rapidly drained and became a river.
Three million years later, the ocean level receded enough to expose
the Central American isthmus and allow mass migration of mammal species
between the Americas.
The ice ages caused tropical rainforests around
the world to retreat. Although debated, it is believed that much of
the Amazon reverted to savanna and montane forest (see Ice Ages and Glaciation). Savanna divided patches of rainforest into
"islands" and separated existing species for periods long
enough to allow genetic differentiation (a similar rainforest retreat
took place in Africa. Delta core samples suggest that even the mighty
Congo watershed was void of rainforest at this time). When the ice ages
ended, the forest was again joined and the species that were once one
had diverged significantly enough to be constitute designation as separate
species, adding to the tremendous diversity of the region. About 6,000
years ago, sea levels rose about 130 meters, once again causing the
river to be inundated like a long, giant freshwater lake.
The massive size of the Amazon and its tributaries make it easy to overlook
the other great rivers and forest ecosystems of the Neotropical realm.
For example, the Orinoco River flows over 1,600 miles through Venezuela.
Interestingly, the Orinoco River system is linked to the Amazon River
basin through a unique natural river system called the Casiquiare
canal. The Casiquiare canal is the only river on the planet which links
two major river systems. To the south of the Amazon is an expanse of
forest that lies in the Tocantins river system. A small area of forest,
greatly reduced by human activity to less than 5 percent of
its original cover, is found along the Atlantic seaboard in Brazil.
The highly threatened Chocò rainforest is found along the northwestern
coast of the continent in Colombia, while the Pacific coast rainforest
runs from Ecuador into Central America.
Much of Central America and many of the Caribbean islands were once
forested with tropical rainforest, although these have been greatly
reduced. Few Caribbean islands still retain any primary forest cover,
while rainforest continues to persist in some parks and reserves in
Central America. Central America suffered the highest percentage loss
of forest of any tropical region between 1990-2005, losing almost 30
percent of its forests.
Today South America suffers the highest total loss of forest—around 4.3 million hectares were cleared per year between 2000
and 2005. Most of the forest loss has occurred in the Amazon
rainforest where large tracts of land are being cleared for cattle ranches
and soybean plantations. Scientists are concerned that forest loss could
escalate in the Amazon due to increasingly dry conditions. In 2005,
the Amazon suffered the most severe drought on record, leaving rivers
dry and communities stranded. Tens of thousands of fires burned.
Total land area
Total forest cover 2005
Primary forest cover 2005
Total deforestation 1990-2005
Loss of primary forest 1990-2005
Country
(1000 ha)
(1000 ha)
% of total land area
(1000 ha)
% of total land area
% of 1990 forest cover
% of 1990 primary forest cover
Belize
2,296
1,653
72.5
612
26.7
0.0
0.0
Bolivia
109,858
58,740
54.2
29,360
26.7
-6.5
-6.5
Brazil
851,488
477,698
57.2
415,890
48.8
-8.1
-9.7
Colombia
113,891
60,728
58.5
53,062
46.6
-1.2
-1.5
Costa Rica
5,110
2,391
46.8
180
3.5
-6.7
-29.4
Ecuador
28,356
10,853
39.2
4,794
16.9
-21.5
0.0
El Salvador
2,104
298
14.4
6
0.3
-20.5
0.0
French Guiana
9,000
8,063
91.8
7,701
85.6
-0.3
-2.6
Guatemala
10,889
3,938
36.3
1,957
18.0
-17.1
-17.0
Guyana
21,497
15,104
76.7
9,314
43.3
0.0
n/a
Honduras
11,209
4,648
41.5
1,512
13.5
-37.1
0.0
Mexico
195,820
64,238
33.7
32,850
16.8
-6.9
-15.3
Nicaragua
13,000
5,189
42.7
1,849
14.2
-20.6
0.0
Panama
7,552
4,294
57.7
3,023
40.0
-1.9
-18.4
Peru
128,522
68,742
53.7
61,065
47.5
-2.0
-2.9
Suriname
16,327
14,776
94.7
14,214
87.1
0.0
0.0
Venezuela
91,205
47,713
54.1
-
n/a
-8.3
n/a
Total Caribbean
23,482
5,974
26.1
0.0
11.7
n/a
Total Central America
52,160
22,411
43.9
0.0
-18.9
n/a
Total South America
1,783,770
831,540
47.7
0.0
-6.7
n/a
Review questions:
Rainforests are generally broken into how many biogeographical realms?
The largest expanse of rainforest is located on what continent?
Most of the rainforest in Africa is found in what basin?
How is African rainforest generally different from rainforests of Asia and South America?
What is the world's second largest island?
Does Australia naturally have monkeys?
What is the Wallace Line?
How did the Ice Ages affect islands and forests in southeast Asia?
True or False—The Amazon River Basin is roughly the size of the forty-eight contiguous United States.
Is the Amazon River the largest river, in terms of volume, in the world?
Is the Amazon River the longest river in the world?
What continent loses the most area of forest each year?
Indonesian palm oil firms pledge to stop clearing rainforests
(5/13/2008) Palm oil companies operating in Indonesia pledged to stop clearing forests for new plantations reports The Jakarta Post. The move is a response to growing criticism that oil palm expansion is destroying biologically-rich rainforests and contributing to global warming.
Unilever calls for ban on rainforest destruction for palm oil
(5/1/2008) Unilever, the world's largest consumer good company, will start using palm oil from certified sustainable sources this year and aims to have all its palm oil certified by 2015, according to a speech delivered today by CEO Patrick Cescau.
No sacrifices to ending deforestation in the Amazon, only gains
(4/29/2008) Regular columnist and co-creator of Brazil's environmental news website, O Eco, Sergio Abranches has great credibility in Brazil's eco-awakening. A professor of political science, Abranches uses his unique talents to reach a widening audience in Brazil for environmental, energy, and climate change news and discussion. He speaks expertly on any number of topics: from Amazonian deforestation to the current food crises to economic and political transformations for a warming world.
