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Tropical rainforests

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Key idea Specification content
Tropical rainforest ecosystems have a range of distinctive characteristics.

 

The physical characteristics of a tropical rainforest.

The interdependence of climate, water, soils, plants, animals and people.

How plants and animals adapt to the physical conditions.

Issues related to biodiversity

Deforestation has economic and environmental impacts.

 

Changing rates of deforestation.

A case study of a tropical rainforest to illustrate: • causes of deforestation – subsistence and commercial farming, logging, road building, mineral extraction, energy development, settlement, population growth • impacts of deforestation – economic development, soil erosion, contribution to climate change.

Tropical rainforests need to be managed to be sustainable.

 

Value of tropical rainforests to people and the environment.

Strategies used to manage the rainforest sustainably – selective logging and replanting, conservation and education, ecotourism and international agreements about the use of tropical hardwoods, debt

TRF Sus dev goal

Sustainable development goal 15

Location – global location of the tropical rainforest

Tropical Rainforests are found in a narrow belt either side of the equator.

TRF map

Climate of the tropical rainforest

Temperatures are hot throughout the year – mainly between 26 & 27 degrees C. Rainfall is heavy and mainly convectional – up to 1800 mm a year. It rains everyday in the afternoon and in every month of the year. Its growing season is 365 days a year – in other words no seasons!TRF Temp

Tropical rainforest an interdependent system

All the parts of the rainforest (climate, water, soil, plants, animals and people) are dependent on one another – if any one of them changes, everything else is affected. For example:

  1. The warm and wet climate means that dead plant material is quickly decomposed by the fungi and bacteria on the forest floor. This makes the surface soil high in nutrients, meaning plants can grow quickly and easily.
  2. Plants pass on their nutrients when they are eaten by animals. The dense vegetation provides lots of food therefore animal populations are high. Many plant and animal species have formed symbiotic relationships (where they rely on each other for survival).
  3. Changes to the forest ecosystem such as deforestation can have knock-on effects within the whole system. Chopping down trees increases the amount of CO2 being absorbed which adds to the greenhouse effect and ultimately changes the climate.
  4. Trees intercept and take up a lot of water, and release it back into the atmosphere, providing moisture for further rainfall. Deforestation means the climate may change and the risk of drought increases affecting plants and animals that live in this ecosystem.
Two houseboats and a boat lie on the bottom of a branch of the Rio Negro, a tributary to the Amazon river, in the city of Manaus, Brazil

Drought in the Amazon rainforest – Manaus

Read the following article – Severe Drought in Brazilian Amazon Leaves Boats High and Dry

Vegetation has a drastic impact on the climate. 

Structure of the tropical rainforest

Emergents – or forest giants, 50 metres or taller. These trees are ususlly supported by buttress roots.

Canopy – This is adense layer forming almost complete cover. Trees 20 – 30 metres tall include many hardwoods such as mahogony.

Under Canopy – This dark and humid area contains saplings between the trunks of larger trees.

Shrub Layer – This contains small trees and shrubs especially near rivers.

Forest Floor – This is covered with ferns and a deep litter of fallen leaves & branches.

TRF Structure

Soil (latosols)

soil

Tropical Rainforest Soils – Latosols

  • Tropical rainforest soils are shallow and acidic – iron oxides stain the top layers red.

  • The soil is infertile and one of the poorest in the world

  • Heavy rainfall quickley washes away any nutrients that are not taken up by the trees

Despite the infertile soil the rainforest survives because

  • Plant and animal remains soon decay in the warm, humid climate

  • Shallow rooted trees quickly absorb the nutrients released by decomposition

  • Few nutrients are lost from the nutrient cycle as the forest literally feeds on itself

  • Most nutrients are stored in vegetation, when they die they decay and are then absorbed by the trees.

Use the following word document to help with the first section of the unit:

Ecosystems – Tropical rainforest

Task
Open the Worksheet (below biodiversity). Sort the statements into a table with the following headings:

1.  Why are rainforests important?
2. Why are rainforests being destroyed?
3. What problems does rainforest destruction cause?

Now use three highlighter colours to show which of the above are social, environmental, economic – add a key at the bottom of your table.

Tropical rainforest -worksheet-biodiversity_card_sort

How plants and animals adapt to the physical conditions

How have plants adapted to the physical conditions?

Factors that help the soils

Previously we saw that the soils in this ecosystem are very poor so how do the plants survive there are four factors:

1 A rapid recycling of nutrients through the ecosystem.

2 The absorption of sunshine, leading to photosynthesis.

3 Warm humid climate is ideal for plant growth throughout the year.

4 Ability of plants to adapt as they compete for sunlight and nutrients

Heat and humidity

Vegetation of the rainforest can deal with the heavy rainfall and heat in various ways e.g. leaves of the tree are waxy and have tips that allow water to run off them. Leaf stems are flexible therefore can follow the sun and maximise photosynthesis.

Plants in the rainforest are adapted to cope with the high rainfall, high temperatures and competition for light:

TRF buttress roots

Buttress roots

  • Tall trees competing for sunlight have big roots called buttress roots to support the trunk.
  • Plants have thick waxy leaves with pointed tips. The drip trips channel the water away from the plant so it is not damaged by the weight.
  • Many trees have smooth, thin bark as there is no need to protect the trunk from the cold temperatures.
  • Climbing plants (lianas) use the tree trunks to climb to the sunlight.
  • Plants drop their leaves gradually throughout the year – allows growth all year round.
TRF drip tip

Drip tip leaves

How have animals adapted to survive in the rainforest?

  • Many animals spend their entire lives high up in the canopy. They have strong limbs fro climbing (howler monkey).
  • Some animals have flaps of skin that allow them to glide between the trees (flying squirrels).
  • Some birds have short wings which allows them to manoeuvre between the trees easily.
  • Some of the animals are camouflaged so they can hide from predators.
  • Many animals are nocturnal – active at night so they can conserve energy during the heat of the day.
  • Many of the forest animals can swim which allows them to cross river channels.
TRF animal frog

Poison dart frog

Use the following word document for the second part of this unit:

Ecosystems Tropical rainforest 

Why is biodiversity so important?

Deforestation

What is the scale of deforestation?

There 62 countries with tropical rainforests within their boarders. About half the worlds tropical rainforest has now been cleared. The scale and accelerating rate of the deforestation has become a global concern.

amazon-deforestation

Deforestation v forest degradation

Human use of the rainforest doesn’t always lead to deforestation in many cases it can be forest degradation. A degraded forest is a secondary forest that has lost, through human activities, the structure, function, species composition or productivity normally associated with a natural forest type expected on that site. This makes it difficult to determine the extent of deforestation.

A degraded forest delivers a reduced supply of goods and services from the given site and maintains only limited biological diversity. Biological diversity of degraded forests includes many non-tree components, which may dominate in the under-canopy vegetation.

amazon sec

Secondary forest – in the foreground there is a secondary forest while the pristine rainforest is in the background.

Causes of deforestation:

Main causes – exploiting activities are: Logging, Mineral extraction, Energy development & Illegal trade in wildlife

Main causes of forest clearing are: Commercial farming – cattle, Commercial farming – crops, Road building, Settlement & population growth.

amazon graph.png

The impacts of deforestation:

Global impacts: Global warming & Loss of biodiversity Local impacts of climate change

Local impacts: Soil erosion and fertility, River pollution, Decline in indigenous tribes & Conflict.

Amazon effects Untitled.png

Soil erosion and landslides – a negative consequence of deforestation

Value of the tropical rainforest

The resources offered by the tropical rainforest are known as goods and services. Goods are things obtained directly from the rainforest (cocoa, sugar, bananas, spices, rubber, chemicals, perfumes, soaps etc.) whereas services are benefits that the forest provides (air purification, water and nutrient recycling, protection against soil erosion, wildlife habitat, biodiversity & employment opportunities).

amazon benefits

Case study of deforestation in the Amazon

Brazil is the world’s fifth largest country, one whose economy has grown and developed rapidly only recently. The Brazilian government sees its rainforest as a vital resource as it continues to industrialise. If the forest is to survive it needs to be protected and conserved, but this has to be balanced with Brazil’s own needs to use the many resources found in it.

amazon 1

Environmental impacts

Soil erosion – no vegetation to hold soil together – gets washed away. Leads to landslides and flooding.

With no interception and absorption by plants more water reaches the soil – this reduces soil fertility as nutrients are washed away.

Trees remove CO2 from the atmosphere. Equally burning the vegetation to clear the forest produces CO2. So, deforestation produces more CO2 which ads to the greenhouse effect.

Economic impacts

Logging, farming and mining create jobs

Money is made from selling timber, mining and commercial farming.

Long term deforestation can destroy the resources that countries depend on e.g. timber and due to this tourist stop going to the area.

Livelihoods of some local people are destroyed

Deforestation in the Amazon has many impacts

Environmental – The Amazon stores 100 million tonnes of carbon – deforestation will release this – cause of global warming. Brazil is losing 55 million tonnes of top soil every year to soil erosion caused by farming.

Economic – Economic development – brought wealth to the country. Farming makes a lot of money for countries in the rainforest e.g. Brazil made $6.9 billion from trading cattle. Mining industry creates jobs e.g. in Peru it hires 3100 people. Logging brings in huge amounts to Brazil Traditional rubber farmers have lost their livelihoods because trees have been cut down.

Brazil

The following PowerPoints deal with deforestation – causes and consequences

Ecosystems – Tropical rainforest 4 , Ecosystems – Tropical rainforests 5 and Ecosystems – Tropical rainforst 6

Read the following article – take notes and answer the questions which follow:

Case Study of a Rainforest Zone: Amazonia

 

 

 

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