Hwa Chong Institution
Sec 2 Geography
Climate and Natural Vegetation
Handout: Characteristics of Natural Vegetation
Name: _____________________________ (
)
Date: _____________
Class: ______
TERMS
Natural vegetation refers to plants that grow naturally in a place with little or no human
interference.
An ecosystem is a community of living organisms (plants, animals and people) within a
physical environment and the interactions between them.
A biome is the living part of an ecosystem and are often classified into vegetation types: forest,
grassland, desert
Climate is the atmospheric conditions of a specific place over a considerable period of time (30
years)
CLIMATE AND THE GLOBAL DISTRIBUTION OF NATURAL VEGETATION
Vegetation in a biome are mainly influenced by climate
-
Temperature (ºC , ºF)
Precipitation (mm)
o Rainfall
o Sleet
o Snow
o Hail
There are 3 climatic types in the world. The climatic regions are dependent on the latitude of the
place
-
Polar Region
o Very low temperatures often below 0ºC for many months
o Very low annual precipitation below 250mm
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Temperate
o Low to moderate temperatures ranging from 0ºC - 38ºC depending on the
season
o Moderate annual precipitation ranging from 300mm – 1000mm
-
Tropical
o High temperatures throughout the year ranging from 20ºC - 30ºC
o High annual precipitation above 1000mm
The distribution of natural vegetation in the world is closely related to the climatic types in the
various latitudes
Climate can influence the growth of natural vegetation in different ways
-
Temperature
o Most plants cannot grow where temperatures have fallen below 6ºC
o This explains the lack of vegetation in places with a polar climate
o Only plants like mosses and lichens can grow there as they are able to adapt to
the very low temperatures
o When temperatures are consistently above 20ºC, the growth of plants especially
trees is abundant
-
Precipitation
o Water is required by plants to make food
o Trees need more water than grasses
o The type of vegetation in an area depends on how much water (amount) is
available and the regularity of its availability
The climate of an area is often shown with a climograph.
TROPICAL RAINFORESTS
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Distribution
Found mainly between 10ºN and S of the equator (between the Tropic of Cancer and Capricon)
Major areas where tropical rainforests can be found are in
- South America : Amazon Rainforest
- Africa: Congo Basin
- Southeast Asia
Characteristics
1) Density and Species
-
The tropical rainforest has dense and luxuriant vegetation because the hot and wet
climate encourages rapid plant growth
-
The trees often grow close together with the crowns touching one another
-
The trees do not grow in pure stands and one hectare of land in the forest may contain
as many as 400 species of trees
2) Structure
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There are five main layers in the tropical rainforest
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The topmost emergent layer is made up of the tallest trees called emergents
o The emergent trees are scattered throughout the forest
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-
o
They grow up to a height of 40m - 50m to reach out for sunlight
o
They have thick and straight trunks with buttress roots to support their size
The canopy layer makes up a large percent of the trees found in the rainforest
o
The trees in the canopy layer grow very close together and their crowns form a
continuous layer called the canopy that prevents most of the sunlight from
reaching the forest floor.
o
Trees in the canopy layer grow up to a height of 15m – 30m
 They can block up to 70% - 90% of sunlight from the forest floor
o
Non-parasitic plants such as lianas and epiphytes can be found in this layer
 Lianas are thick woody vines that start off growing on the grown but twine
up the trees for sunlight
 Epiphytes (ferns and orchids etc) grow on trees to obtain sunlight but
make their own food and do not feed off the host plant
 Rainwater and decaying leaves that collect at the joints of the
branches provide epiphytes with water and nutrients
o
Parasitic plants are also found in this area. They grow on the host plant and
eventually kill them. An example is the strangler fig.
The understorey layer is made up of small trees which grow where gaps in the canopy
allow sunlight to pass through
o The trees grow up to the height of 5m – 15m
o
-
The shrub layer consists of shrubs, ferns and young saplings
o The trees grow from the ground up to a height of 6m
o
-
Lianas and epiphytes are also found in this layer
They grow in areas where gaps in the canopy allow them to receive sunlight
The ground layer/ undergrowth layer has sparse vegetation because very little
sunlight reaches the forest floor
o Saprophytes are found here. They do not photosynthesise and live on dead and
dying organic matter
 Examples include fungi and mushrooms which help to break down leaf
litter and dead organic matter on the forest floor
3) Evergreen
-
Trees in the tropical rainforest are evergreen in appearance throughout the year and do
not shed their leaves as the high temperature and high rainfall provide them with enough
water and sunlight to survive throughout the year.
4) Leaves
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Leaves are generally broad and dark green to take in as much sunlight as possible
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They are thick and leathery to withstand the heat in the equatorial region
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They are smooth and waxy so that rain water can run off them easily and many of them
have downward pointing drip tips to allow excess water to drip off.
o
This prevents water from collecting on the leaves which may encourage the
growth of harmful bacteria
5) Bark
-
The bark is generally smooth and thin as there is no necessity for protection against
extreme cold or dry weather
6) Roots
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The roots are shallow as the high rainfall provides most of the water which can be found
in the top layer of the soil
-
Nutrients in the tropical forests are also found in the top layer of the soil because of the
rapid amount of decayed leaves, twigs and branches
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The larger trees have buttress roots that can reach 1m – 5m above the ground to
support the heavy weight of the tall trees.
7) Branches
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The branches of the trees are found at the top one-third of the trees so that they are able
to obtain maximum light for photosynthesis
-
Many are shaped like umbrellas as they spread out their leaves to obtain the most
amount of sunlight
8) Flowers and fruits
-
As the air is generally still in the dense forest, the vegetation mainly depends on
animals, birds and insects to spread pollinate the flowers or to spread their seeds
o
o
Flowers are normally colourful and sweet smelling to attract birds and insects
Fruits are normally sweet and fleshy to attract animals
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TROPICAL MANGROVE FORESTS
Distribution
Mangrove forests can be found in are found between 23.5° north and 23.5° south of the equator
in areas with a tropical climate,
They are found along sheltered coastlines and places where rivers deposit sediment, such as
river mouths.
-
Rainfall in mangrove forests is between 1000mm and 2000mm.
Examples include Sungei Buloh in Singapore and the Sundarbans in Bangladesh.
Characteristics
1) Density and Species
-
Mangrove forests have dense vegetation because of high temperatures and rainfall.
The canopy is dense and little sunlight gets through to reach the ground, resulting in
sparse undergrowth.
-
Only a small number of trees can survive in the salty conditions along the coast.
-
Mangrove trees, however, are halophytes, which are highly specialised plants that have
adapted to growing in salty conditions.
-
These trees provide valuable resources such as food, medicine, firewood, construction
materials and charcoal.
2) Structure
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Tropical monsoon forests are divided in three distinct horizontal zones.
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Trees in the coastal zone are nearest to the sea have adapted to growing in salt water
and have breathing roots or aerial roots known as pencil-like roots.
•
Trees in the middle zone have prop roots or stilt roots to lift them out of the sea water
during high tide and give trees support.
•
The inland zone contains trees that are least tolerant to salt water. These trees have
knee-like roots to give them support.
3) Evergreen
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Trees in the tropical mangrove forest are evergreen which means that they do not shed
their leaves at the same time.
o
The climate in a tropical region allows the plants to get sufficient sunlight and
water throughout the year
o
The location of the mangroves near the sea also give them unlimited access to
water throughout the year.
4) Leaves
•
Leaves of mangrove trees are broad to absorb sunlight and have drip tips to allow rain to
flow off quickly.
•
They are also thick and leathery to prevent water loss.
•
Some leaves contain glands that allow them to secrete excess salt.
•
Salt is also stored in old leaves which then fall off and remove the salt from the tree.
5) Bark
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The bark is generally thin and smooth as there is no extreme weather and there is no
need for protection.
6) Roots
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The roots of mangrove trees are specially adapted to the muddy, waterlogged soil, and
also to the waves that occur along the coastline.
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Trees in the coastal zone have aerial roots to allow them to breathe even though they
are underwater.
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Other types of roots include prop roots that help anchor the tree firmly and also help to
lift it out of the sea water at high tide.
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Mangrove trees further inland have knee-like roots that provide firm support on the soft
soil.
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Finally, some mangrove trees have special membranes that can filter salt from the water
that it absorbs.
7) Flowers and fruits
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Mangrove tree flowers are generally colourful in order to attract insects.
-
Because mangrove trees live near the sea, some of their fruits are buoyant and can float
on water.
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This allows them to be carried away on the water to other areas of the coast where they
can germinate.
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Other types of fruits begin to grow while still on the parent tree.
-
Such fruits also have sharp tips to anchor themselves into the soil. These adaptations
allow the fruits to start growing into trees immediately.
CONIFEROUS FORESTS
Distribution
Found mainly between 60ºN – 70ºN and 60ºS - 70ºS of the equator
Major areas where tropical monsoon forests can be found are in
- Russia
- Canada
- Norway (Europe)
- Sweden (Europe)
- Finland (Europe)
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Characteristics
1) Density and Species
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The coniferous forest is not as dense as the low temperatures and precipitation cannot
support large numbers of vegetation
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Only a few species grow in the conifnerous forest because not many plants can adapt to
the low temperatures and precipitation
-
The trees grow in pure stands and which means only a single species or a mix of 2-3
grow in an area in the forest
2) Structure
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There are two main layers in the coniferous forest
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The topmost layer the canopy layer makes up a large percent of the trees found in the
rainforest
o
-
The trees are generally uniform in height and have no distinct layers among the
vegetation.
o Trees in the canopy layer grow up to a height of 20m – 30m
The ground layer/ undergrowth layer is sparse due to the low amount of sunlight
received in the temperate region
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There is also low soil nutrient level because the leaf litter is made up of though needles
which do not break down easily.
-
The cold temperatures also reduce the rate of decomposition.
3) Evergreen
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Trees in the coniferous forest are deciduous which means that they shed their leaves
over the same period of time annually
o
The trees do not shed their leaves
o
They retain their leaves so that photosynthesis will still take place during the cold
season whenever the temperature rises above 6ºC
4) Leaves
-
Leaves are needle-like and have small surface areas
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The small surface area helps to reduce water loss through transpiration since there is
low precipitation in the area
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Some of the leaves are also able to store water for use when the water is frozen as ice.
5) Bark
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The bark is generally thick and rough for protection against the long cold winters
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6) Roots
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The trees have shallow spreading roots which help them to obtain water easily from the
soil surface when the snow melts
7) Branches
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Tree branches are flexible and downward sloping to enable snow to slide off easily
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This prevents snow or ice from accumulating on them, causing the branches to break off
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The conical shape of some trees also help them to withstand strong winds
8) Flowers and fruits
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Trees bear cones instead of flowers and fruits
The cones protect the seeds from the cold and are dispersed by either wind or animals.
NATURAL VEGETATION: Forests as a Resource
FORESTS
SUPPLY
REGULATORY
PROTECTIVE
REGULATORY
Forests contribute directly to the natural ecosystem and help to regulate it.
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Quantity of Water
o
Forests help in maintaining the water cycle

As vegetation transpires, water vapour is released into the atmosphere

Water is collected on leaves through the process of interception and the
water is returned to the atmosphere when it evaporated

Water vapour eventually condenses and falls back as rain


It is estimated that half of the amount of rain in tropical countries is
a result of the evaporation of moisture from the forests’ canopies
When forests are cleared, evaporation and transpiration are affected and
the quantity of water intercepted by the tropical rainforest’s canopy is
greatly reduced.
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Quality of water
o
o
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Vegetation cover and the roots of the trees helps to protect the soil from soil
erosion which can cause waterways to be filled with impurities and soil particles

Vegetation cover intercepts the rainwater and reduces the speed and flow
of rainwater on the surface of the ground (surface runoff)

Hence the water collected in the river is of a better quality
Mangrove forests has the ability to process the waste materials that have been
deposited in water bodies

Deomposing dead animals and water contamination by soil erosion

Industrial and domestic waste
Quality of the soil
o
Vegetation helps to contribute to the fertility of the soil through decomposition of
leaf litter on the forest floor
o
The nutrient cycle
 Nutrients such as nitrogen and phosphorus are critical for the survival and
reproduction of plants

o
-
Decomposing matter on the forest floor releases the required nutrients
back to the soil as humus
Vegetation helps to maintain the soil quality by reducing the amount of soil loss
through soil erosion
Quality of the air
o
Forests take in carbon dioxide from the atmosphere and give out oxygen during
the day through the process of photosynthesis
o
This helps to regulate the amount of carbon dioxide in the atmosphere

Replaces carbon dioxide given out by human activities with oxygen

Forests are carbon sinks and help store carbon in their trunks. Carbon is
released back into the atmosphere when the trees are cut down and
burnt.
SUPPLY
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Habitat for flora and fauna / people
o
Forests provide food and shelter for living organisms
o
They also provide shelter for indigenous tribes and people who stay in them
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o
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Resources
o
The construction industry gets its supply of building materials like wood from the
forests
 Some developing nations depend on the sale of timber to achieve
commercial gains
o
Fuelwood and charcoal are traditional sources of energy and in many developing
nations, people rely heavily on them as a source of energy for heating and
cooking in homes
Medicines
 Some plant species in the forest have medicinal value that can be used to
treat diseases
o
o
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The forest habitat also provides people with the food that they need to survive

Quinine found in the rainforest is used to treat Malaria

The US National Cancer Institute has identified 3000 plants that
have active uses against cancer cells
o
70% of these plants are found in the rainforest
o
25% of the active ingredients in today’s cancer-fighting
drugs come from organisms found only in the rainforest
Chemicals
 Some trees provide chemicals that are used as resources
 Resin from coniferous trees are made into wood varnishes and
ointments

Tannin found in rhizophora mangroves are used to treat leather

Latex from rubber trees are processed into rubber sheets to make
rubber products
Recreation
o
Forests are recreational places for locals to rest and relax
 Bukit Timah Nature Reserve as a place to trek and jog
o
Forests are also tourist destinations and help attract tourists to the country
 Bukit Timah Nature Reserve in Singapore
 Sungei Buloh Wetland Reserve in Singapore
 Alishan Forest in Taiwan
 Taman Negara in Malaysia
Research and Education
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Ideal and conducive environment for researchers to conduct research and
experiments
 Search for new food crops and medicines

Understanding how the forests are affected by climate change

Understanding how the forests can regulate the effects of climate change
PROTECTIVE
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Flood prevention
o The root system provides stability and protection to the soil structure
o
-
Soil erosion is minimized
 River channels are able to maintain their depths and will not become
shallower due to sedimentation
 Likelihood of rivers overflowing their banks are reduced and floods are
prevented
Coastal protection
o Mangrove forests act as buffer zones for coastal settlements against destructive
waves

They can dissipate or break the initial force of incoming waves and
weaken the wave energy significantly

Coastal settlements lying behind the wall of mangroves are
protected against severe destruction and flooding
o
o
During the 2004 Indian Ocean Tsunami, mangrove forests
protected some coastal villages in southern India
Mangroves are able to protect the surrounding waters against pollution

The roots of the mangroves trap waste materials and provides a filtering
effect by reducing the amount of pollutants flowing into the larger water
bodies

The soil in the mangrove forest contains bacteria that can breakdown the
biodegradable wastes and convert them into nutrients for the mangrove
trees
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