2011 sec 3 elective geography chapter 03 • types of natural vegetation

Chapter : Natural Vegetation

A Study of the Earth’s Forests

Chapter 3: Natural Vegetation

• Topics covered:– Global distribution of the different types of

forests– Characteristics of the different types of forest– Adaptations of each type of forest to its

environment


• 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, including plants, animals and people, within a physical environment and the interactions between them.


• Therefore, natural vegetation (plants) are only a part of the larger ecosystem that also includes animals and humans.

• However, natural vegetation plays an important role in every ecosystem because it provides food and shelter for animals.


• Natural vegetation can be grouped into 3 major types:– Forests– Grasslands– Deserts

• These vegetation types are known as biomes.


• A biome refers to the living part of an ecosystem.

• Hence, there are forest biomes, grassland biomes and desert biomes.

Forest biome: Tropical rainforest

Forest biome: Temperate deciduous forest

Forest biome: Coniferous forest

Forest biome: Mangrove forest

Forest biome:Tropical monsoon forest

Grassland biome: Tropical grassland

Grassland biome: Temperate grassland

Desert biome: Hot desert vegetation

Desert biome: Cold desert vegetation (tundra)

Why are there different types of natural vegetation?

• There are many types of natural vegetation mainly due to the different types of climate experienced in different parts of the world

• Temperature affects vegetation because if it is too cold (less than 6°C), few plants can grow. On the other hand, warm temperatures (above 20°C) allow abundant plant growth.


• Precipitation (rainfall) also affect vegetation because all plants require water to grow.

• Most trees require more water to grow than grass.


• Hence, most forests grow in areas with high rainfall (above 1000 mm a year).

• In areas with moderate precipitation of between 200 mm and 1000 mm, grasslands are more common.

• In areas with less than 200 mm of rain, deserts are found.

Location of Different Types of Natural Vegetation

• It is therefore not surprising that different types of vegetation can be found in different parts of the world, depending on the amount of rainfall and the average temperatures found in those places.

• See the map on the following slide and describe the distribution of four different types of natural vegetation.


• As you can see from the map:– Temperate coniferous forests can be found

mainly far from the equator in the northern hemisphere (between 60°N and 70°N of the equator).


• As you can see from the map:– Tropical rain forests are found mainly along the

equator while tropical monsoon forests are found slightly further away from the equator.

– However, both these types of forests are found in the tropics (between 23.5°N and 23.5°S of the equator).

– Mangrove forests can be found in coastal tropical regions.

Tropical rainforests• Tropical rainforests can be found in areas

with a tropical equatorial climate.• Such places are located between 10°N and

10°S of the equator, with high rainfall of above 1500 mm a year and temperatures of above 27° throughout the year.

• The three largest rainforests are the Amazon rainforest, the Congo basin rainforest and the rainforests in South-east Asia.

Tropical rainforests

Tropical rainforests: Structure• Tropical rainforests

have a structure of five distinct layers:

• Emergent layer: trees with a height of 30m to 50m have long, thick and straight trunks and emerge from the canopy layer. SHRUB LAYER

UNDERGROWTH

Tropical rainforests: Structure• Canopy layer: trees

have a height of 15m to 30m and have wide, umbrella-shaped crowns that block sunlight from reaching the lower layers of the forest.

SHRUB LAYER

UNDERGROWTH

Tropical rainforests: Structure• Understorey layer:

shorter trees with a height of 6m to 15m grow; they have oval-shaped crowns to catch sunlight passing through gaps in the canopy; younger trees are also found here. SHRUB LAYER

UNDERGROWTH

Tropical rainforests: Structure• Shrub layer: young

trees and woody plants are found here, growing up to 6m high.

SHRUB LAYER

UNDERGROWTH

Tropical rainforests: Structure• Undergrowth layer:

grasses, mosses and fungi grow sparsely here due to lack of sunlight; plants reach maximum height of 5m.

UNDERGROWTH

SHRUB LAYER

Tropical rainforests: Structure

• Some plants, called epiphytes overcome the shortage of sunlight by growing high up on tree branches to get sunlight (examples: ferns, orchids).

• Other plants, known as lianas, grow upwards to get more sunlight by winding around tree trunks.

Epiphytes

Lianas

Mushrooms (Fungi) growing on the forest floor

Tropical rainforests: Structure

• Parasitic plants such as the strangler fig can also be found in the understorey and canopy layers.

• However, due to the lack of sunlight, the are few plants growing in the undergrowth, which is made up mostly of decaying leaf litter.

Parasitic strangler figs

Tropical rainforests: Diversity

• Tropical rainforests support the largest diversity of plant species of any biome on earth.

• Scientists estimate that on average, one hectare of rainforest contains 750 species of trees and 1500 species of other plants.

• Many species of hardwood trees such as chengal and meranti can be found.

Tropical rainforests: Density

• Tropical rainforests are also very dense, with trees growing close together.

• The large number of trees is due to the high rainfall and temperatures that allow plants to grow rapidly and in great numbers.

Tropical rainforests: Leaves

• Tropical forest trees are evergreens as the leaves remain green throughout the year.

• This is unlike deciduous trees, which shed their leaves in the autumn or in the dry seasons.

• The leaves are also large to absorb as much as much sunlight as possible.

• They are also waxy and have drip tips to allow water to drain off.

Tropical rainforests:Fruits and flowers

• Trees in the tropical rainforest have brightly-coloured flowers to attract insect pollinators.

• They also have sweet-smelling fruits and flowers to attract animals for seed dispersal.

Colour and variety of flowers in the

tropical rainforest

Rafflesia flow

er, which uses the sm

ell of rotti

ng flesh to attract insect pollinators

Tropical rainforests: Leaves

• The bark of trees in the tropical rainforest is thin because they are not required to protect the trees from dry or cold conditions.

• Branches are also located in the top one-third portion of the trunks and they are shaped like umbrellas to capture as much sunlight as possible.

Tropical rainforests: Roots

• Roots of tropical forest trees are shallow because they do not need to reach deep into the soil for water.

• This also allows the roots to tap the abundant nutrients found in the layer of leaf litter of on the ground.

• Some of the tallest trees have buttress roots to support their great weight and prevent them from falling over.

Tree roots near the surface, Malaysia

Tropical monsoon forests

• Tropical monsoon forests can be found in tropical areas in bands 10° and 25° north and south of the equator.

• They grow in areas with high temperatures (about 26°C) and rainfall (over 1500mm).

• However, unlike tropical rainforests, it is found in areas with distinct wet and dry seasons.

• Examples can be found in India and northern Australia.

Tropical monsoon forests

Tropical monsoon forests: Structure

• Unlike the tropical rainforest, the tropical monsoon forest has only three layers.


• Canopy layer: 15m to 30m in height, but the trees are more spread out, this allowing sunlight to pass through.

• Other plants such as creepers, vines, epiphytes and parasitic plants can also be found.


• Understorey layer: Younger trees can be found here, about 6m to 15m in height.


• Undergrowth: the undergrowth contains bamboo and grass.

• During the wet season, there is dense vegetation, but there is less dense vegetation during the dry season.

Contrast between monsoon forest during the dry and wet seasons

Tropical monsoon forests: Diversity

• There are only about 200 species of plants in a tropical monsoon forest, compared to about 1500 in a tropical rainforest.

• This is because few plants can survive a long time without water during the dry season.

• However, many valuable species of hardwoods such as teak and sandalwood can be found.

Tropical monsoon forests: Density

• Tropical monsoon forests are less dense then tropical rainforest as the trees do not grow as closely to each other.

• As a result, there are gaps in the canopy, which allow sunlight to pass through.

• This allows dense undergrowth to develop, especially during the wet season.

• During the dry season, the undergrowth becomes more sparse due to lack of water.

Tropical monsoon forests: Leaves

• Tress in tropical monsoon forest are deciduous, which means that their leaves fall off at certain times of the year.

• This occurs during the dry season to allow trees to conserve water.

• Leaves are also waxy and have drip tips as there is heavy rain during the wet season.

• Some plants, such as the bamboo, have narrow leaves to minimise water loss.

Tropical monsoon forests: Flowers and fruits• Flowers and fruits in

tropical monsoon forests are not as colourful or sweet-smelling as those in the tropical rainforest.

• They also tend to flower and bear fruit during the dry season.

Flowers and fruits of the com

mon

teak tree (Tectona grandis)

Tropical monsoon forests: Bark and branches

• Tropical monsoon forest trees have thick and coarse bark that protects them from heat, dryness and even forest fires during the dry season.

• Branches are also located in the middle section of the trunk instead of near the top because sunlight is able to reach the lower parts of the forest.

Red beech tree bark, Australia

Tropical monsoon forests: Roots

• The roots of trees in tropical monsoon forests are deep in order to tap water during the dry seasons.

Mangrove forests

• 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, especially 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.

Map showing location of mangrove forests

Mangrove forests: Structure

• Tropical forests are divided in three distinct horizontal zones.


• Trees in the coastal zone are nearest to the sea have adapted to growing in salt water and have breathing roots or aerial 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.

Mangrove forests: Diversity

• 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.

Mangrove forests: Density• Mangrove forest has

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.

Mangrove forests: 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.

Mangrove leaves show

ing their thick, leathery texture

Mangrove leaves with salt glands

Salt water being excreted by glands on leaves

Salt crystals forming on the

leaf of a mangrove tree

Another type of mangrove

leaves with salt glands

Mangrove forests: Flowers and fruits

• 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.

• This allows them to be carried away on the water to other areas of the coast where they can germinate.


• 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.

Mangrove forests: Roots• The roots of mangrove

trees are specially adapted to the muddy, waterlogged soil, and also to the waves that occur along the coastline.

• Trees in the coastal zone have aerial roots to allow them to breathe even though they are underwater.

Mangrove forests: Roots

• 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.


• Mangrove trees further inland have knee-like roots that provide firm support on the soft soil.


• Finally, some mangrove trees have special membranes that can filter salt from the water that it absorbs.

Coniferous forests

• Coniferous forests can be found in areas which experience a cool temperate continental climate.

• These areas can be found between 60° and 70° north of the equator.

• Such places experience summer temperature of 21°C and winters as cold as -40°C.

• Precipitation is low, with only 300 mm to 635mm throughout the year. In winter, this precipitation falls as snow.

Map showing the location of coniferous forests

Coniferous forests: Structure

• Coniferous forests have only two layers. • The canopy layer is made up of trees which

grow to a uniform height of between 20m to 30m.

• Trees are grow close together but not as closely as trees in tropical rainforests.

• The undergrowth layer has very little vegetation because of the low amount of sunlight and the poor fertility of the soil.

Coniferous forests: Diversity

• Due to the harsh, cold conditions, only a few species of trees grow in coniferous forests.

• These include softwood trees such as pine, spruce and fir trees, which are useful for making paper, matches and furniture.

• Often, coniferous forests contain only one to three species of trees growing in a forest.

Blue spruce

Fraser fir

Coniferous forests: Density

• Due to cold temperatures and lack of sunlight, trees in coniferous forests cannot grow as densely as those in tropical rainforests.

Coniferous forests: Leaves

• The leaves in coniferous forests are evergreen and are not shed.

• This allows the trees to make full use of the short growing season in summer.

• Leaves are also needle-like to minimise water loss.

Coniferous forests: Flowers and fruits

• Coniferous trees produce cones instead of flowers and fruits like most other trees.

• These cones protect the seeds inside from the extremely cold conditions.

• Also, the cones can be either male or female (and they can both be on the same tree).

Coniferous tree showing both

male and fem

ale cones

Coniferous forests: Roots

• Coniferous trees have shallow spreading roots which enable them to absorb water from the surface during the short warm months.

• Roots do not go deep as the ground there may be permanently frozen, even during the summer.

Summary: Importance of Forests

• In this chapter, we have learnt about four types of forest and the adaptations they have to survive in their environments.

• In the next chapter, we will examine the importance of forests to both the Earth, as well as to the humans who live on it.

2011 sec 3 elective geography chapter 03 • types of natural vegetation

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