chapter 9 types of natural vegetation

Earth: Our Home

Full Geography

Chapter 9

Types

of

Natural Vegetation

You will learn:

• to describe the global distribution of

different types of forests

• to describe the characteristics of different

types of forests

• to compare the ways in which different

types of forests adapt to the environment

Learning Outcomes

•Global distribution of tropical rainforests,

tropical monsoon forests, mangroves and

coniferous forests.

•Characteristics and adaptations of tropical

rainforests, tropical monsoon forests,

mangroves and coniferous forests.

•Skills

- Compare and contrast the characteristics

of different forests.

What is Natural Vegetation?

• Natural vegetation refers to plants that

grow naturally in a place with little or no

human interference.

• It plays an important role in a forest

ecosystem by providing food and shelter

for the animals and native people that live

in the forest.

Major types of natural vegetation

Tropical rainforestTemperate

deciduous forest

Coniferous forest

Grassland biome

Grasses constitute the main plants in a grassland

biome. It has few varieties of plants.

Tropical grassland Temperate grassland

Desert biome

The vegetation in a desert biome consists of mainly sparse vegetation, such as scrubs and tough grasses in the hot desert,

and mosses and lichens in the cold desert. It has very few varieties of plants.

Hot desert vegetationCold desert

vegetation (tundra)

Forest biome

The vegetation in a forest biome consists of mainly trees. It generally has many varieties of plants.

Distribution of Natural

Vegetation

• Climate is a major factor in influencing the

distribution of natural vegetation.

• There are 3 climatic types..


VegetationVery low temperatures, often below 0ºC. Very low annual precipitation,

below 250 mm

Low to modern temperatures, ranging from 0°C to 34°C,

depending on the season. Moderate annual precipitation,

300 mm to 1 000 mm

High temperatures throughout the year, 20°C to 30°C.

High precipitation, above 1 000 mm

Temperate region

Polar region

Tropical region

Tropical region

Temperate region

Polar region


Vegetation

• Temperature and precipitation can

influence plant growth.

• Plant growth is more abundant in areas

where temperatures are consistently

above 20C than in areas where

temperatures fall below 6C.


Vegetation• Water is required by plants to make food.

• Thus, different types of natural vegetation forests are found in different parts of the world.

- forests --- high precipitation at above

1 000 mm per year.

- grasslands --- moderate precipitation

between 200 mm to 1 000 mm per year.

- hot desert vegetation or tundra --- no or

little precipitation at less than 250 mm per

year.


Vegetation

Tropical forests are a cradle of biodiversity. It has

been estimated that half of the plant and animal life

forms that live on this planet are found in this

environment, even though tropical forests cover

only six percent of the earth’s surface. Source: The Tropical Rainforest by Francesco Petretti, Journey Editions, 1998, Italy.

Tropical Rainforest• Tropical rainforests

- found in places 10°N & S that experience the tropical equatorial climate

- high temperatures, about 27C

- high amount of rainfall, above 1 500 mm

throughout the year

- examples of tropical rainforests include

the Amazon Basin in South America,

Congo Basin in Africa and parts of

Southeast Asia

Tropical Rainforest

• Structure of the forest

- 5 layers:- Emergent layer, 30 m to 50 m

- Canopy layer, 15 m to 30 m

- Understorey layer, 6 m to 15 m

- Shrub layer, grow up to 6 m

- Undergrowth layer, grow up to

5 m

Tropical RainforestEmergent layer 50 m

Tall trees, called emergents, reach a height of 30 m

to 50 m. Their crowns appear above the canopy

layer. These trees have tall, thick and straight trunks.

30 m

Canopy layer

The trees in this layer reach a height of 15 m to 30

m. Their wide, shallow and umbrella-shaped crowns

form a continuous leaf cover, called a canopy, as

they prevent sunlight from penetrating into the lower

layers of the forest. 15 m

Understorey layer

The trees here have narrower, oval-shaped crowns

because most of the sunlight is blocked by the

canopy. These trees grow where gaps in the canopy

allow sunlight to pass through. Their heights range

from 6 m to 15 m. Young trees of the emergent and

canopy layers are also found in this layer.

6 m

Shrub layer

Tree saplings and woody plants are found in this

layer. They may grow up to 6 m high.

5 m

Undergrowth layer

The undergrowth or forest floor is made up of

grasses, ferns, mosses and fungi. Plant growth is

sparse because very little sunlight reaches this layer.

Plants in this layer reach a maximum height of 5 m.

0 m

Tropical Rainforest• Characteristics of the 5 layers

Emergent layer

- trees have tall, thick and straight trunks

Canopy layer

- tree crowns inter-lock

- presence of epiphytes and lianas, and parasitic plants

Understorey layer

- trees with narrower crowns

- presence of parasitic plants

Shrub layer

- tree saplings and woody plants found

Undergrowth layer

- sparse due to lack of sunlight that reaches the forest floor

Tropical Rainforest• Characteristics

- a wide diversity of plant species

- 750 species of trees and 1 500 species of other plants

in 1 hectare

- the high temperature and rainfall throughout the year

enables it to support a large variety of plants

• Density

- extremely dense

- density is due to high temperature and rainfall that

encourage abundant vegetation growth

Tropical Rainforest• Characteristics and Adaptations

Leaves

- are evergreens

- due to high rainfall throughout the

year, trees do not shed leaves at the

same time

- are waxy with drip tips

- to allow rainwater to drain off easily

Tropical Rainforest

• Characteristics and Adaptations

Flowers and fruits

- are colourful and sweet-smelling

- to attract insects for pollination and

animals for seed dispersal

Tropical rainforest


Bark and branches

- thin and smooth branches

- does not need protection against cold or dry conditions

- branches are found at the uppermost one-third of the

trunks to get as much sunlight as possible

Roots

- shallow and spreading

- nutrients are found at topsoil due to high decomposition

- buttress roots (of some tall trees)

- support weight of trees

Tropical Monsoon Forest• Tropical monsoon forest

- found in the tropics

- high temperatures, about 26C

- high amount of rainfall, above 1 500 mm

throughout the year, but with distinct wet

and dry seasons

- located in South Asia, Southeast

Asia,southern China and northern

Australia

Tropical Monsoon Forest• Distribution

Tropical Monsoon Forest

• Structure of the forest

3 layers: - Canopy layer, 25 m to 30 m

- Understorey layer, about 15 m

- Undergrowth layer

Tropical Monsoon Forest30 m

Canopy layer

Trees can grow to 25 to 30 m

in height. They are more

spread out than those in a

tropical rainforests, plants such

as creepers, vines, epiphytes

and parasitic plants are found

within this layer.

15 m

Understorey layer

The trees in the understorey

are about 15 m in height.

6 m

Undergrowth

Bamboo thickets and grasses

grow densely here during the

wet season. They are

dense during the dry season.

0 m


• Characteristics of the 3 layers

Canopy layer

- more spread out than those in tropical rainforest

- presence of epiphytes and lianas, and parasitic plants

Understorey layer

- consists of shorter trees about 15 m in height

Undergrowth

- bamboo thickets and grasses grow densely here

during the wet season but are less dense during dry

season


• Characteristics

Diversity of plant species

- about 200 species in 1 hectare

- less species compared to tropical rainforest

due to inconsistent rainfall

Density

- plant growth is abundant but less dense than

tropical rainforest


• Characteristics & Adaptations

Leaves

- are deciduous

- shed leaves during the dry season to minimise

loss of water through transpiration

- waxy with drip tips to allow rainwater to drain

off easily



Bark and branches

- thick and coarse

- protects the trunk from heat and dryness

during the dry season

- withstand extreme heat from natural — forest

fires

- branches found around middle of trunks as

trees grow less dense than tropical rainforest



Roots

- deep tap roots

- to tap water sources deep under the

ground as rainfall is irregular throughout

the year

Tropical forests in a glance

• What are the similarities between the

tropical rainforest and the tropical

monsoon forest?

• What are the differences?

Tropical forests in a glance

• Similarities

- both forests are dense

- leaves are waxy with drip-tips

Answers

Tropical rainforest Differences in

terms of

Tropical

monsoon

forest

more diversity less

denser density less dense

evergreen leaves deciduous

Smooth, thin bark

Branches at top one-

third

bark &

branches

Thick bark

Branches around

middle of tree

shallow roots deep tap roots

Mangrove forests• Found mainly in areas experiencing

tropical climate, along sheltered coastal

regions and places where rivers constantly

deposit clay and silt.

Mangrove Forests

• Structure

- grows to a height of 2 m to 40 m

- horizontal zones of mangrove species

Mangrove Forests

Coastal area

Avicennia and Sonneratia trees are

common in this zone, which is the

nearest to the coast. They have adapted

to growing in salt water, as the coastal

zone is flooded with seawater during

high tide. The trees have breathing

roots or aerial roots.

Middle zone

Rhizophora trees are common in this

zone. They have prop roots or stilt roots.

Inland zone

Bruguiera trees grow further inland, as

they are the least tolerant of salt water.

They have knee-like roots.

Low tide

High tide

Mangrove Forests


- four main species which are known as halophytes

- Avicennia, Sonneratia, Rhizophora, Bruguiera

- dense and luxuriant

Leaves

- evergreen

- salt secretors

- ultrafiltrators

Mangrove Forests• Characteristics and Adaptations

Flowers

- generally colourful to attract insects to pollinate

Fruits

- buoyant so that waves and currents can carry them

away

- elongated with sharp tips to anchor in soft muddy soil

Mangrove Forests


Roots

- aerial roots that are exposed

- allow them to take in oxygen

- prop roots

- anchor the trees firmly in the muddy soil

Coniferous Forests

• Coniferous forest

- found in places that experience a cool

continental climate

- experiences seasons

- temperatures range from -40C to 21C

- low amount of precipitation, usually in the form

of snow, 300 mm to 635 mm in a year

- located in Alaska, northern Canada, northern

USA, northern Scandinavia and Russia

• Distribution

Coniferous Forests

Coniferous Forest

• Structure

- no distinct layers

- generally uniform in height, about 20 m

to 30 m

- trees grow close together

- little undergrowth

Coniferous forests


Diversity

- few species as not many trees can adapt to the climate

- the trees grow in pure stands

Density

- forest are not dense as the climate does not support dense vegetation growth

Coniferous Forest

• Characteristics

Leaves

- evergreen

- retain leaves so that photosynthesis can take

place whenever temperature rises above 6C

- needle-like with small surface area to reduce

water loss due to transpiration

- store water for use in winter

Coniferous Forest


Flowers and Fruits

- trees bear female and male cones

- female cones produce seeds

- male cones produce pollen

- cones can be dispersed by wind or

animals after pollination

Coniferous forest


Bark and branches

- thick bark

- to protect from long, cold winters

- flexible branches that slope downwards

- to enable snow to slide off easily

Roots

- shallow, spreading roots

- enable trees to absorb water easily from soil

surface when snow melts

Importance of Forests

• Support diversity of plants and animals.

• Natural habitats for animals.

• Provide us with resources.

• Home to some natives.

• Part of our natural heritage.

Learning Outcomes

•Global distribution of tropical rainforests,

tropical monsoon forests, mangroves and

coniferous forests.

•Characteristics and adaptations of tropical

rainforests, tropical monsoon forests,

mangroves and coniferous forests.

•Skills

- Compare and contrast the characteristics

of different forests.

chapter 9 types of natural vegetation

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