Natural Vegetation

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Earth: Our Home Full Geography

Chapter 9Types

of Natural Vegetation

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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

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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.

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Major types of natural vegetationTropical rainforest Temperate

deciduous forestConiferous 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.

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Distribution of Natural Vegetation

• Climate is a major factor in influencing the distribution of natural vegetation.

• There are 3 climatic types..

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Distribution of Natural Vegetation

Very 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

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Distribution of Natural 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.

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Distribution of Natural 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.

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Distribution of Natural Vegetation

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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.

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Tropical Rainforest• Tropical rainforests

- found in places 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

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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

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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

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Tropical Rainforest• Characteristics of the 5 layers

Emergent layer - trees have tall, thick and straight trunksCanopy layer- tree crowns inter-lock- presence of epiphytes and lianas, and parasitic plantsUnderstorey layer- trees with narrower crowns- presence of parasitic plantsShrub layer- tree saplings and woody plants foundUndergrowth layer- sparse due to lack of sunlight that reaches the forest

floor

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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

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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

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Tropical Rainforest• Characteristics and Adaptations

Flowers and fruits- are colourful and sweet-smelling - to attract insects for pollination and

animals for seed dispersal

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Quick Quiz• Can you identify the

flower?

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Quick Quiz• It is a type of Rafflesia, a spectacular plant

found in the tropical rainforest.• There are 15 to 19 species of Rafflesia.• Rafflesia is known to produce the largest

individual flower on the Earth.

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Tropical rainforest• Characteristics and Adaptations

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

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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

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Tropical Monsoon Forest• Distribution

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Tropical Monsoon Forest• Structure of the forest

3 layers: - Canopy layer, 25 m to 30 m - Understorey layer, about 15

m - Undergrowth layer

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Tropical Monsoon Forest 30 m

Canopy layerTrees 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 layerThe trees in the understorey

are about 15 m in height.

6 m

UndergrowthBamboo thickets and grasses

grow densely here during the

wet season. They are

dense during the dry season.

0 m

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Tropical Monsoon Forest• Characteristics of the 3 layers

Canopy layer- more spread out than those in tropical rainforest- presence of epiphytes and lianas, and parasitic plantsUnderstorey layer- consists of shorter trees about 15 m in heightUndergrowth- bamboo thickets and grasses grow densely here

during the wet season but are less dense during dry season

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Tropical Monsoon Forest• 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

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Tropical Monsoon Forest• 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

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Tropical Monsoon Forest• Characteristics & Adaptations

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

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Tropical Monsoon Forest• Characteristics & Adaptations

Roots- deep tap roots- to tap water sources deep under the

ground as rainfall is irregular throughout the year

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Tropical forests in a glance• What are the similarities between the

tropical rainforest and the tropical monsoon forest?

• What are the differences?

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Tropical forests in a glance• Similarities- both forests are dense- leaves are waxy with drip-tips

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Tropical forests in a glance• Differences diversitydiversity

densitydensity

leavesleaves

bark & bark & branchesbranches

rootsroots

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AnswersTropical rainforest Differences in

terms of Tropical

monsoon forest

more diversity less

denser density less dense

evergreen leaves deciduousSmooth, thin barkBranches at top one-third

bark & branches Thick barkBranches around middle of tree

shallow roots deep tap roots

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Mangrove forests• Found mainly in areas experiencing

tropical climate, along sheltered coastal regions and places where rivers constantly deposit clay and silt.

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Mangrove Forests• Structure

- grows to a height of 2 m to 40 m- horizontal zones of mangrove species

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Mangrove Forests

Coastal areaAvicennia 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 zoneRhizophora trees are common in this

zone. They have prop roots or stilt roots.

Inland zoneBruguiera trees grow further inland, as

they are the least tolerant of salt water.

They have knee-like roots.

Low tide

High tide

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Mangrove Forests• Characteristics and Adaptations

- four main species which are known as halophytes - Avicennia, Sonneratia, Rhizophora, Bruguiera- dense and luxuriant

Leaves- evergreen- salt secretors- ultrafiltrators

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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

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Mangrove Forests• Characteristics and Adaptations

Roots- aerial roots that are exposed- allow them to take in oxygen- prop roots- anchor the trees firmly in the muddy soil

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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

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• Distribution

Coniferous Forests

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Coniferous Forest• Structure

- no distinct layers- generally uniform in height, about 20 m

to 30 m- trees grow close together- little undergrowth

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Coniferous forests• Characteristics and Adaptations

Diversity- few species as not many trees can adapt to

the climate- the trees grow in pure standsDensity- forest are not dense as the climate does not

support dense vegetation growth

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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

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Coniferous Forest• Characteristics and Adaptations

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

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Coniferous forest• Characteristics and Adaptations

Bark and branches- thick bark - to protect from long, cold winters- flexible branches that slope downwards - to enable snow to slide off easilyRoots- shallow, spreading roots- enable trees to absorb water easily from soil

surface when snow melts

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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.

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Learning Outcomes•Global distribution of tropical rainforests, Global distribution of tropical rainforests, tropicaltropical monsoon forests, mangroves and monsoon forests, mangroves and coniferous forests.coniferous forests.•Characteristics and adaptations of tropical Characteristics and adaptations of tropical rainforests, tropical monsoon forests, rainforests, tropical monsoon forests, mangroves and coniferous forests.mangroves and coniferous forests.•SkillsSkills-- Compare and contrast the characteristicsCompare and contrast the characteristics of different forests.of different forests.