Sec 1 Chapter 3 Tropical Rainforests

Chapter 3
Tropical Rainforest
How Can We Save The
Rainforest?

Think about this!
How did the name tropical rainforest come about?
TROPICAL
RAIN
FOREST

Tropical Rainforest
In this section, you will explore these Guiding
Questions:
1. What are tropical rainforests?
2. Where can they be found?
3. What is deforestation and which areas have been
deforested?
4. Why does deforestation occur?
5. How does deforestation impact people and the
environment?
6. How should we manage deforestation?

• Watch a video of the tropical rainforest.
Take note of the features of a tropical
rainforest.

Which photo do you think shows a tropical rainforest?

Characteristics of tropical rainforest
• Thick and luxuriant
• Broadleaved (to capture sunlight for
photosynthesis)
• evergreen trees – they do not shed all their
leaves at the same time.
• Found in areas that experience high rainfall
(about 1,500 – 2,500 mm annually) and high
temperature (about 26oC) throughout the year

• Diversity of plant species
• Structure of tropical rainforest

Diversity of plant species
• Hot and wet environment gives rise to rich
biodiversity (range of plant and animal species found
in an area)
In Amazon rainforest in
South America
In forests in
United Kingdom
300 different plant species
within 0.01 km2
(1 football field)
40 plant species
within 27,000 km2

Diversity of plant species
• Different types of food can be found:
– Fruits (e.g. bananas, mangoes)
– Spices (e.g. pepper, cinnamon)
– Vegetables (e.g. corn, pandan)
– Nuts (e.g. Brazil nuts, walnuts)

Structure of the tropical rainforest
A tropical rainforest has primarily three layers:
• Emergent layer (above 30 m)
• Canopy layer (20–30 m)
• Undergrowth layer (below 20 m)

• Watch a video that describes the structure of
a tropical rainforest.

Characteristics of tropical
rainforest
Structure of the tropical
rainforest
• Emergent layer (above 30 m)
– Uppermost layer where some
trees rise and tower above
other trees
– Can grow up to 50m – 80m
– The emergent layer is formed
by the crowns of these trees.
– Trees in this layer usually have
tall, straight and smooth
trunks with few branches
– E.g. Tualang tree, Kapok tree

rainforest
Structure of the tropical
rainforest
• Canopy layer (20 – 30 m)
– The trees grow to heights of
20 – 30m to reach for
sunlight.
– Trees grow close together
(dense)
– Crowns interlock to form an
almost continuous cover
– This blocks up to 90% of the
sun’s rays from reaching the
forests floor

Canopy layer (20 – 30 m)
• Lianas: Thick,
woody vines that
twine up trees to
reach for sunlight.
• Epiphytes: Plants
which grow on trees to
reach more sunlight
(includes ferns,
orchids, mosses,
lichens)

rainforest
• Undergrowth layer (below 20 m)
– Dark because sun’s rays blocked
by the canopy.
– Plants are small, thin and widely-
spaced due to lack of sunlight.
– Consists of plants such as moss,
ferns, some lianas and epiphytes.
– They have much larger leaves
compared to those in the other
layers
– Thin layer of leaf litter due to
rapid decomposition caused by
hot and wet environment.

Adaptation of plants
• Leaves
– Leaves are broad
• Helps trees capture sunlight for photosynthesis
– Leaves have waxy, leathery or hairy surfaces
• Helps to minimise the loss of moisture through
transpiration due to the high temperatures

• Leaves
– Some leaves have narrow,
downward pointing tips (drip
tips)
• Allow water to run off easily
• Prevents fungi and bacteria
from growing on the leaves

• Fruit and flowers
- colourful and strong-smelling
to attract insects and other
animals to assist in seed
dispersal and pollination
Air is usually still (lack of wind)
which is hard for seed dispersal and
pollination by wind
Fruit of the cacao plant
Rafflesia, the world’s
largest flower

• Roots
– Buttress roots which grow
from 1 – 5 m above the
ground
• To support the heavy
weight of tall trees

• Roots
– Shallow roots
• Nutrients from the rapid decomposition of fallen leaves
and branches are mostly found in the top layer of the
soil
• Water is available throughout the year, therefore there
is no need for the roots to grow deep to search for
water.

Uses of tropical rainforests
a. Water catchment
b. Green lungs of the earth
c. Habitat to flora (plants) and fauna (animals)
d. Habitat to indigenous people
e. Source of timber
f. Medical application

a) Water catchment
• Refers to an area drained by a river and the smaller
rivers that flow into it
Rain falls in tropical rainforests
Trees stop rain from reaching the ground directly
Water slowly drips from the trees
Contributes to water supply
• Because impurities in rainwater are trapped in the
soil before it flows into the reservoirs, forests help
to maintain the quality of water.
Seeps into the ground and is
stored as groundwater
Flows as runoff into the rivers
or reservoirs

b) Green lungs of the earth
• Tropical rainforests help the earth to ‘breathe’
– More than 20% of the earth’s oxygen is generated by
the Amazon rainforest
– Absorb carbon dioxide from the atmosphere and
release oxygen (photosynthesis)
– They act as the earth’s natural air purifier as they
absorb 2.4 billion tonnes of carbon dioxide in one
year.
• Dense vegetation of tropical rainforests keeps the
earth cool

c) Habitat to flora (plants) and fauna (animals)
• Home to more than 2 million species (1/2 of world’s
species)

Habitat to flora (plants) and fauna (animals)
• Abundance and diversity of flora and fauna
– Ample sunlight is converted by the plants into energy
and food (photosynthesis) which allows plants to
thrive
 In turn, the plants are eaten by animals for survival
– Continuous canopy is a habitat where other plants can
grow and animals can live in

d) Habitat to indigenous people
• 60 million indigenous people
(original inhabitants of a country)
are wholly dependent on the
tropical rainforest
• been living in tropical rainforests
for thousands of years
e.g. Yanomami (Amazon rainforest),
Penan (rainforest in Sarawak)
An indigenous group living in the
Amazon rainforest

Habitat to indigenous people
• Tropical rainforests provide these people with daily
necessities (food, clothing and medicine)
• They obtain food by either hunting and gathering
(hunt fish, gather wild fruit and nuts), or agriculture
(growing of crops)
[As such, they are known as hunter-gatherers or shifting
cultivators]

e) Source of timber
• Timber refers to the the wood (e.g. teak, ebony,
mahogany and meranti) used to build or make things
such as doors, window frames and furniture
• Tropical rainforests supply about 1/5 of the world’s
industrial timber
• provide fuel wood to people for cooking

f) Medical application
• In Amazon rainforest, nearly 3,000 plant species have
been identified to have medicinal properties
• Many of the foods (e.g. Brazil nuts) have cancer-
fighting properties

Medical application
25% of all modern
medicines come
from rainforest
plants

• Medicine in the Rainforest

• People value the rainforest for different reasons

World distribution of tropical rainforests
2. Where are tropical rainforests
found?

Global distribution of tropical rainforests
• Less than 5% of the earth’s land surface
• Equatorial climate (between latitudes 20° N and 20°
S) where there is abundant sunlight, high
temperatures and heavy rainfall throughout the year
• High annual temperatures (of more than 26oC, with
a range of 2–3oC) and high annual rainfall (1,500–
2,500mm)
• Main areas : Amazon Basin, the Congo Basin,
Southeast Asia.
2. Where are tropical rainforests found?

World distribution of tropical rainforests
2. Where are tropical rainforests found?
Amazon Basin in
South America
Congo Basin
in Africa
Southeast
Asia

Latitudes
• Are imaginary horizontal lines that run in
an east-west direction around the Earth.
• The Equator is the longest line of latitude
– it divides the Earth into two equal
halves (Northern and Southern
Hemisphere)

Latitudes
• Latitudes are
measured in
degrees and
minutes from the
Equator
• They increase in
value as they
move northward
and southward.

Distribution of tropical rainforests in Singapore
• Many parts of Singapore were originally covered with
rainforests
• After 1819: Rainforests were rapidly cleared to grow
crops and build infrastructure
• 1882: Only 7 per cent of the original rainforests
remained
• Today: Rainforests occupy an area of about 20 km2
(3% of total land area) and are mainly found at the
Central Catchment Nature Reserve and Bukit Timah
Nature Reserve
3a. Where are tropical rainforests found?

found?
1819

found?
2006

3. What is deforestation? (p86)
Spot the difference
An area in the Amazon rainforest

3. What is deforestation?
Deforestation
• It is the cutting down and removal of all or most of
the trees in a forested area
• If not managed properly, it can lead to the
permanent destruction and eventual disappearance
of a once renewable resource
1980 1990
Tropical Rainforest 19.1 mil km2 17.9 mil km2

3b. Which areas have been deforested?
Global distribution of deforested areas of tropical
rainforest
• Rainforests are disappearing at alarming rates
because of human activities:
– Agriculture
– Mining
– Logging
– Land clearance (for housing and industries)
• Remaining rainforests are smaller and broken up into
fragments

rainforest
At least 320 km2 of tropical rainforest
disappear each day

rainforest
Areas of tropical rainforest that have been deforested

rainforest (TB p92)
Tropical rainforest loss in some countries
Do “Let’s try it!” on pg 93

rainforest
Deforestation estimates of tropical
rainforests in Borneo
• If the present rates of
deforestation in the
world continue, our
world’s remaining
rainforests could be gone
in one hundred years.
• In Borneo, logging is one
of the main reasons that
caused rapid
deforestation.

• Agricultural activities
• Cattle ranching
• Logging
• Mining

Agricultural activities
Agriculture is the growing of crops and raising of
animals to provide food
• Shifting cultivation (a form of subsistence farming
activity)
– Have been the traditional cause of deforestation
– Shifting cultivators grow crops for their own use and
consumption
– They allow land to regain its fertility and for
vegetation to regrow when they move to the next
plot of land
As such, does not pose a major threat to the forest

• Large-scale commercial agricultural activities on
plantations
– Burn and clear large areas of the rainforest
– Crops are grown for cash and are sold to meet
both local and global needs
As a result, the rate of deforestation has increased
greatly!

Example:
• By 2010, about 242,000 km2 of
the Amazon rainforest have
been converted into soya bean
farms
– Major ingredient in food for
cattle
– Also, processed into products
such as soya milk and tofu
Large areas of rainforest are being cleared
for soya bean farms in the Amazon Basin

Cattle ranching
Involves operating large farms to raise cattle
• Large areas of rainforest are cleared to create land
for cattle to graze
Large tracts of the Amazon
rainforest are being lost to cattle
ranching
For example:
• 80% of deforestation in the
Amazon rainforest is caused by
land cleared for cattle ranching
• 1986: Less than 10 million head
of cattle
• 2011: 79 million head of cattle

Cattle ranching
• A large amount of beef from cattle in the Amazon is
exported to other countries (e.g. USA, Britain)

Logging
The cutting down of trees for timber
• Commercial logging of tropical hardwoods (teak,
mahogany, rosewood) to make furniture, building
materials and charcoal
• Growing demand for timber products
 Increases logging activities
Commercial logging is responsible
for destroying 50,000 km2 of
tropical rainforest every year!

Logging
• Logging reduces the number of trees and damages
the rainforest as a whole
Why?
• For every tree extracted, five are badly damaged
(falling tree will destroy the surrounding trees or
smaller-sized plants)
• Also, the soil is exposed to erosion

Logging
Example:
• To meet needs in China
– Huge demand for timber for making disposable
chopsticks and paper
– Caused heavy logging in the rainforests of Congo
and Cameroon in Central Africa, Brazil and
Indonesia

Mining
• Precious metals and
gemstones (gold, copper and
diamonds) are found
beneath many tropical
rainforests
• Forests are cleared to
establish the mines and
construct roads to transport
the mined materials
NASA satellite image showing the
extent of deforestation caused by the
Carajás Mine, Brazil

Mining
Example:
• Carajás Mine in Brazil has a rich variety of mineral
reserves
• In 2007: 296 million tonnes of iron ore were extracted
(18 billion tonnes of minerals including gold and
copper)
• These minerals are needed to produce electronic
products such as computers and telephones as well as
electrical wires

Although human activities have led to
deforestation, some may view these activities as
key to development:
• The clearing of forests provides land for
communities to build houses, factories, offices
• Roads can be built and this makes trade and
transport easier
• Also, the land can be converted to agricultural land
to allow the production of more food

5. How does deforestation impact people and
the environment?
Environmental impact
• Loss of biodiversity
• Loss of water catchment areas
• Increased risk of flooding, soil erosion and
sedimentation
• Enhanced greenhouse effect
Economic impact
• Depletion of natural resources
Social impact
• Effects on indigenous people

Loss of biodiversity
• Deforestation destroys the habitats of plants and
animals
• Loss of biodiversity = Loss of the variety of plants and
animals -> extinction of plant and animal species ->
lesser variety of resources (eg. Food, medicine, timber)
• Changes in biodiversity may increase the occurrence of
insect-borne diseases (e.g. malaria, dengue fever)
• lack of nutrients in the soils may not be able to support
the biodiversity that once existed on that land
the environment?

Loss of watch catchment areas
• Forests play an important role in maintaining our
water supply
• They enable water to be collected and stored within
a water catchment area
the environment?

Loss of watch catchment areas
The Amazon Basin has 7,000 tributaries
Countries
surrounding the
Amazon
rainforest
depend on
water from the
Amazon Basin,
especially
during dry
seasons
the environment?

Loss of water catchment areas
• Clearing of trees disrupts the water cycle  Less
transpiration happening, less rain  drier climate and
drier soils as the ground no longer contains and receives
as much water  decreased water supply  higher
water prices
the environment?

Increased risk of flooding, soil erosion and
sedimentation
• When trees are cleared, the ground is left bare
• No trees, moss and leaf litter to intercept and reduce
the impact of rain on the ground.
• More surface runoff, less infiltration
• This causes flooding in the surrounding areas
the environment?

sedimentation
the environment?

Increased risk of flooding, soil erosion and sedimentation
• Soil erosion is the removal of the top layers of soil by
rainwater, wind and destructive human activities (logging)
• When trees are removed  no roots to hold the soil, no
trees to intercept the rain  land becomes exposed  soil
erosion  rain washes the soil into rivers  increases the
amount of sediments in the rivers affects water quality
and aquatic life
• Increased amount of sediments smothers fish eggs,
resulting in lower hatch rates
• Turns water cloudy and prevents sunlight from penetrating
the water  suffocates coral reefs.
the environment?

sedimentation
Sediments enter
the sea
Coral reefs get suffocated
Sediments will eventually
settle and accumulate
the environment?

Enhanced greenhouse effect
• The gases (eg. Carbon dioxide, methane, water vapour and
others) in the atmosphere help keep the earth warm.
These are known as greenhouse gases. The warming of the
atmosphere is known as the greenhouse effect.
Without the greenhouse effect, the earth’s average
temperature will be −18°C rather than the current 15°C
• Human activities such as setting up of industries, transport
network and power station have increased the amount of
greenhouse gases in the atmopshere  more heat
trapped in the atmosphere increases the earth’s
temperature Enhanced greenhouse effect
the environment?

• Deforestation contributes to enhanced greenhouse
effect  increased amount of carbon dioxide in the
atmosphere
• Less trees means that less carbon dioxide is absorbed
and more of it remains in the atmosphere.
• The burning of rainforests also releases carbon dioxide
into the atmosphere. Branches and logs that are left
behind become fuel for forest fires.
the environment?

Deforestation of
tropical
rainforest
contributes
significantly to
the total
amount of
carbon dioxide
released into
the atmosphere
the environment?

• The enhanced greenhouse effect affects people and
the environment
For example
• Increased temperatures can cause ice caps to melt
• Results in a rise in sea levels and flooding of low-lying
coastal areas
• Low-lying islands (Kiribati and Vanuatu in the Pacific
Ocean) may be submerged and disappear into the sea
• As such, people living on these islands may lose their
homes
the environment?

Economic impact
Depletion of natural resources
• Natural resource: Anything from the natural environment
that people can use to satisfy their needs such as food,
shelter, clothing, air and water
• Tropical rainforests provide important natural resources
(timber, food and water) for human needs, and they
contribute greatly to the economic growth of many
countries
• Rapid deforestation often destroys the rainforest faster than
it can replenish itself  depletion of natural resources 
affects earnings of industries that rely on rainforest
resources.
the environment?

Economic impact
Depletion of natural resources
Earnings of
industries that rely
on rainforest
resources get
affected
e.g. timber trade
the environment?

Social impact
Effects on indigenous people
The Guarani
community (Brazil) is
living in makeshift
camps because parts of
the forest were cleared
for sugarcane
plantations, displacing
these people from their
homes in the tropical
rainforest
the environment?

Social impact
Effects on indigenous people
• Indigenous people live in harmony with the forest and
obtain their needs, such as food and shelter, from it.
• Cutting down rainforests affects the lives of indigenous
people
• They lose their homes and are forced to adapt to a new
ways of living to survive  causes indigenous tribes to
disperse and cultures to disappear
the environment?

The worrying state of our world’s rainforests
signals a need for action!
The blue line shows the amount of forests that will be lost from 2012 onwards if we do nothing and continue with deforestation.
The red line shows a target we can meet if we take action.

• Conservation: It is the
protection of the
environment and its natural
resources from harm . It
involves maintenance,
restoration and wise
management of resources to
avoid permanent depletion
of resources

International Year of Forests (IYF) 2011
• Sustainable resource management: It refers to the
careful use of resources to ensure their availability in
the future
• To achieve this, laws need to be passed & everyone
needs to play his part.

4 strategies of managing deforestation
• Protection of forested areas
• Reforestation
• Controlled logging
• Public education

Managing deforestation in the Amazon
Protection of forested areas
- Laws are passed to protect the tropical
rainforests from unfavourable activities that
might endanger the biodiversity and natural
resources.
- The indigenous tribes living in these areas are
also preserved.
- The Central Amazon Conservation Complex is
the largest protected area in the Amazon Basin.
It is set aside for the conservation of the
biodiversity, education and research

Benefits
• Important in the conservation of our indigenous
ecosystems and native biodiversity
• Useful for educational and recreational purposes,
and scientific study
• Has helped to reduce deforestation in the Amazon

Challenges
• - Protected areas are not fenced and are still vulnerable
to human impact
• In the Amazon, officers responsible for monitoring the
protected areas may give in to corruption and allow
loggers and miners to illegally enter protected areas
• - There are not enough forest rangers to patrol the huge
areas of the Amazon rainforest  families illegally
settling in the protected areas

Managing deforestation in the
Amazon
Reforestation
- Non-profit organisations,
companies and local communities
are involved in the reforestation
projects in the Amazone
rainforest.
Eg. Reforestation in Peru
• Organised by LATA (Latin America
Travel Association) Foundation
• Buy seedlings from and pays local
communities to plant trees. 70,000
trees were planted in 2011

Benefits
Reforestation
• Reforestation improves soil fertility  sustained
plant growth.
• Reduces erosion, maintains the water cycle, and
preserves the rainforest habitat and biodiversity
• Creates more jobs for local communities e.g.
producing seedlings to plant, tour guiding

Challenges
Reforestation
• Can be expensive and time-consuming
• Depends on the availability of native plants for
reforestation

Controlled logging
• Allows logging only in certain areas and in sustainable
manner (eg. Only selected plant species can be logged)
• Ways to control logging:
-impose penalties (fines & imprisonment) on irresponsible
timber companies
-through education & research programmes, timber
companies are informed of the damage done and the
necessary measures need to be taken to manage the
damage.

Benefits
Controlled logging
• Greater control of illegal logging has led to a decrease in
deforestation in the Amazon
• In recent years, Brazil’s environmental enforcement
agency has stopped several illegal loggers
The Brazilian Institute of Environment and Renewable
Natural Resources
• Programme: Every tree that is logged is accounted for
• Prevents total clearance of a forest
• Benefits shared with locals who help run this programme

Challenges
Controlled logging
• Identifying and logging selected trees is time-
consuming and difficult to implement
• Areas designated for controlled logging in the
Amazon still face threats from illegal loggers as the
rainforest covers a large area, making it difficult to
track illegal loggers

Public Education
1. Publications – magazines published by World Wide Fund
for Nature (WWF) informing people about rainforests.
2. Ecotourism – activities organised by MT Amazon
Expeditions to the Amazon rainforests.
3. To people of other countries - Embassy of Brazil in
Singapore launched an “Amazonia in Singapore Exhibition”
which showcased the biodiversity of the rainforest and
raised awareness of management and conservation
strategies

Benefits
Public education
• Helps to change people’s mindsets, and increase
awareness, understanding and appreciation of
forests
• Knowledge and awareness can lead to action and
participation from the community

Challenges
Public education
• Turning environmental awareness into personal
behaviour and action is difficult
• Raising awareness is difficult in some countries with
low literacy rates
• Many of the countries around the Amazon rely on the
rainforest and these countries obtain income from
exports derived from the rainforest

Discussion
What can you, as an individual, do to contribute
to the global/local efforts to save the rainforest?

Sec 1 Chapter 3 Tropical Rainforests

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