CHAPTER 6 Environmental functions of Tropical rainforests and how are they used by people

What are the functions of tropical rainforests?

Generation of oxygen

Contribution to carbon storage

Providing habitats for species diversity

Providing protection from soil erosion

How is oxygen generated?

Plants and trees carry out photosynthesis to produce oxygen, in which the trees and plants absorb carbon dioxide, water and sunlight to produce food for their survival and give out oxygen in the process

What is the special trait of oxygen produced in the rainforest?

Trees are evergreen, hence oxygen is produced all year round as the tropical trees can photosynthesise all year round.

What is the special name of forests (with regard to oxygen production?)

Green lungs of the earth.

How do tropical rainforests help the earth?

They help the Earth ‘breathe’

• more than 20% of Earth’s oxygen is generated by the Amazon rainforest

• They 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.

What are some processes of the oxygen cycle?

Respiration → CO2

Decomposition → CO2

Fossil fuels + fossils → industrial combustion → CO2

Plant respiration → CO2

photosynthesis → O2

Contribution of carbon storage, elaborate

Rainforests and mangroves absorb carbon dioxide from the atmosphere during photosynthesis.

What is this process of storing carbon?

Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide

It is one method of reducing the amount of carbon dioxide in the atmosphere with the goal of reducing global climate change

Elaborate on carbon sequestration

Carbon dioxide in the atmosphere is absorbed by plants and stored within leaves, branches, trunks and roots

Roots of plants also produce soil carbon

As a forest grows, the amount of carbon dioxide that is held within the forest increases → Tropical forests are good carbon storage

The CO₂ held is only released when a plant dies → when a plant decomposes, it is broken down by the decomposition process → CO₂ is released into the atmosphere

Mangroves, are they good at storing carbon, and why?

They are effective carbon storers

Soil in mangroves is waterlogged and has few bacteria to break down the carbon stored there.

Additionally, the waterlogged soil contains very little oxygen, which is necessary for decomposition

Thus, materials in waterlogged soil cannot decompose easily, and the carbon continues to be stored and not released into the atmosphere → → Waterlogged soil in mangrove forests is able to store more carbon per unit area

Carbon storage, tropical rainforests vs mangroves

Mangroves

~60-80kg of carbon/km² every year

Rainforests

~20-59kg of carbon/km² every year

How do trees get their mass?

As trees photosynthesis, they form carbohydrates, which make the tree’s biomass

CO₂ is taken in at a certain rate and builds the mass of the tree over time.

What happens when trees die?

Most of its carbon is not released back into the atmosphere as CO₂ , but remains stored in forest soils and wetlands, making forests an essential tool in reducing greenhouse gas emissions from fossil fuels

Whats an exception? (death of trees carbon emissions)

BUT if the trees are harvested and processed into long-lasting wood products (lumber or pulp/paper), the dead tree will keep its stored carbon out of the atmopshere

Explain providing habitats for species diversity

TRFs have warm climate, an abundance of rain and food sources all year round providing a suitable habitat for life

Talk about the diversity and provide statistics

TRFs contain the LARGEST variety of flora and fauna in the world

• More than 1000 species of freshwater fish and birds live in TRFs

• Potentially over 2 million species of insects (weaver ants, rhinoceros beetles etc) may be found in TRFs and only a small fraction has been discovered and named.

Why do rainforests have an abundant diversity of flora and fauna?

Ample sunlight to help plants grow and the plants are eaten by animals

The continuous canopy provides the habitat for the plants to grow and animals to live.

Mangroves promote diversity of species by? (fishes)

They provide breeding grounds for young fish, as their dense root networks provide shelter from predators

Mangroves promote diversity of species by? (shrimps and fish fry)

supporting shoals of shrimp and schools of fish fry, as their roots serve as hiding grounds for small aquatic animals, as the spaces between the roots are too small for larger predators

Mangroves promote diversity of species by? (migratory and local birds)

serving as nesting grounds

Why is there an abundant diversity of flora and fauna in the mangroves?

Dead leaves and branches that fall from mangrove plants are broken down by bacteria into tiny particles which fishes, shrimps and crab feed on. These smaller animals are in turn eaten by larger predators such as otters, crocodiles and even tigers.

Why is soil erosion bad?

Soil is needed for plants to grow, but soil erosion causes soil to be removed from the ground

Why is this bad in TRFs?

They receive high amounts of rainfall (ave 2000mm) throughout the year, and when trees are removed, there won’t be natural vegetation to provide cover to prevent surface run-off and hence nutrients in the topsoil will be washed away.

Explain protection from soil erosion (shoot system bio =)

The canopy layer’s leaves, branches and stems of rainforest plants slow down falling raindrops before they reach the ground → allow time for infiltration, less water becomes surface runoff

The raindrops hit the soil with less force and do not cause the soil particles to be detached and washed away by flowing water, resulting in soil erosion

Explain protection from soil erosion (root system)

Roots of rainforest plants help to hold the soil together in place and prevent soil from being washed away easily

More rainwater can infiltrate and percolate into the soil, thus reducing surface run-off.

What happens if the area is not protected by vegetation?

Rain falls directly onto the ground with considerable force, and this causes soil particles to become dislodged or loosened.

The intensity of rainfall that impacts the ground prevents the water from infiltrating or percolating into the ground layer. If the rain falls too quickly, the soil may not be able to absorb all of the rainfall immediately.

This means more water remains on the surface, leading to more surface runoff

The loosened soil particles are easily washed away by the surface runoff

This leads to severe soil erosion.

What are the characteristics of the ecosystem before deforestation?

Many trees offer soil protection from rain erosion

Many leaves fall to the forest floor as litter

Nutrients from litter form a layer of topsoil (humus)

Soil retains water, increasing chemical weathering and the release of minerals from rock

Few nutrients are lost by leaching, leading to very nutritious soil

Nutrient-rich soil promotes rapid vegetation growth.

Effects of deforestation

Very few trees offer protection for the soil

A few leaves dropped as litter

Less nutrient-rich soil is produced (very little humus)

Rapid loss of nutrients by leaching results in acidic soil (ferralitic soil)

A change in composition (mineral content/pH) renders soil infertile

Infertile soil results in very little vegetative growth

What do mangroves do against coastal erosion?

Mangroves protect coastal areas from erosion as they help to reduce the power of strong waves and storms.

How do mangroves protect coastal erosion? (roots)

The dense root systems of mangrove plants help to trap and stabilise loose sediments on the coast so sediments are less likely to be washed away by waves, currents and tides.

How do mangroves protect coastal erosion? (roots, trunks n branches)

The roots, trunks and branches of mangrove plants cause friction with waves hitting the coast so the waves lose a significant amount of energy, reducing wave erosion

What are TRFs used for?

As a habitat

For raw materials

Recreation purposes

Agriculture

Medicinal cures

Elaborate habitat

About 60 million ppl live in tropical forests

• Yanomami in the Amazon rainforest and the Penan in the rainforest in Sarawak

• Rainforest provides the indigenous people with daily necessities such as food, clothing and medicine.

Examples of indigenous communities living in tropical rainforests

Korowai People

• Live on the island of New Guinea in Indonesia

• They forage for food and materials in rainforests

• They have little contact with cities and urban centres.

Moken people

• Sea nomads who live along the mangrove shores of Southern Myanmar and Thailand

• Hunt for fish in the mangroves and trade the fish for rice and other basic necessities

• Use mangrove wood to construct traditional houseboats or simple huts to live in

Moken people (might not need to study)

• exceptional knowledge of the ocean and marine life. Livelihood is traditionally totally dependent on the resources of the sea, so spear fishing is vitally important to them.

• Unusually good underwater vision because their eyes have adapted to the liquid environment. Even without weights, they are negatively buoyant enough to walk across the bottom of the sea as if hunting on land

…. pg 6

elaborate on what types of raw materials are used by people and what they use it for (wood)

• One of the most valuable products from tropical rainforests is the wood, also known as lumber or timber

• Tropical woods such as mahogany, rosewood and teak are valued for their durability and colour

• People like to use tropical wood for carpentry work and to make other wood-based items

elaborate on what types of raw materials are used by people and what they use it for (ores)

Some places, there are raw materials like copper, diamonds, gold and oil found underneath tropical rainforests

Trees are cut down to explore potential mining areas, and then cleared in huge numbers to exploit whatever mineral has been found. Often explosives are used which is particularly damaging in terms of animal habitats.

For example?

Amazon has lots of gold - around 50 000 hectares of land is being used for gold mining.

The Amazon rainforest is home to the Carajas mine, which is the world’s biggest iron ore mine.

Elaborate recreational purposes

• city dwellers visit TRFs to appreciate and get close to nature

• Spending time in nature is beneficial in reducing stress

• Sights, sounds and smells of a TRF have a calming effect on visitors and improve their well-being

• Activities: Camping, hiking, and birdwatching

Elaborate on agriculture (livestock production)

Farming is also extremely damaging to the rainforest. Huge areas are cleared for cattle ranching, which accounts for around 80% of the destruction in the Amazon rainforest

Mainly to supply higher-income countries with beef (e.g. USA and Canada)

Cattle need large areas to graze, but the quality of pasture declines fairly quickly, meaning farmers have to move their herds onto new areas, which means clearing even more areas.

pg 14 need to do??

Elaborate on agriculture (cropping)

Huge areas are also cleared for crop plantations for cash crops like palm oil, soybeans and coffee, which all have vast plantations

Because of over-cultivation, the soil is quickly stripped of nutrients, so farmers then move and search for more land

The demand for sugar cane and biofuel is increasing rapidly, leading to even more destruction.

need to do 16-17??

What else occurs in rainforests? (agriculture farming)

Subsistence farming also takes place, which often uses slash and burn cultivation, where areas of land are burnt to create fertile ash, but these fires can get out of control, causing destruction.

Why are mangroves precious?

Provides wood that is valuable as it is water resistant, which can be used for:

Construction scaffolding

Boats

Jetties

Homes and charcoal

Medicinal cures, elaborate

Some 120 prescription drugs sold worldwide today are derived directly from rainforest plants

According to the U.S. National Cancer Institute, more than 2/3 of all medicines found to have cancer-fighting properties come from rainforest plants

Example of medicine derived from rainforest

Ingredients obtained and synthesised from a now-extinct periwinkle plant found only in Madagascar (until deforestation wiped it out) have increased the chances of survival for children with leukaemia from 20% to 80%

Need to do pg 21?