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Threats to Tropical Rainforests » Threats to Rainforests and the Impacts of Deforestation

What you'll learn this session

Study time: 30 minutes

Cambridge spec: 3.4.1, 3.4.2

The main threats to tropical rainforests and how each one causes damage
The environmental impacts of deforestation
The social and economic impacts, from local to global scale
Examples from South America, Asia and Africa

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Why rainforests are under threat

Rainforests are rich in timber, minerals, oil and land. The people who live near them, and the companies and governments far away, all want to use these resources. Remember, deforestation is the clearing of trees. It is the biggest single threat, and most of the other threats lead to it.

Key terms:

Logging: cutting down trees for timber, paper and fuel.
Cattle ranching: raising large herds of cattle on cleared land for meat and leather.
Commercial farming: growing crops to sell for profit, often on large farms.
Subsistence farming: growing food mainly to feed the farmer's own family.
Slash-and-burn: cutting down and burning a patch of forest to clear land for crops.
Habitat: the natural home of a plant or animal.

The threats and how they cause damage

Threat	How it damages the rainforest
Logging	Valuable trees such as mahogany are cut for timber. Heavy machines and the tracks they use knock down many other trees and crush the soil.
Mining (resource exploitation)	Forest is cleared for the mine and its roads. Chemicals such as mercury, used to separate gold, pollute rivers and kill fish.
Oil extraction (resource exploitation)	Forest is cleared for wells and pipelines. Spills and leaks poison the soil and water, as in the rainforest of Ecuador.
Road and railway building	The route is cleared, and the new access lets loggers, miners, farmers and settlers move deep into the forest.
Cattle ranching	Large areas are cleared for grass. Cattle trample the soil, which is soon used up and eroded, so ranchers clear more forest.
Commercial farming	Huge plantations of palm oil and soya replace the forest. Palm oil is used in food and cosmetics, and soya is mainly fed to animals.
Subsistence farming	Families use slash-and-burn. The ash feeds crops for a few years, then the soil is exhausted and they must clear new land.
Hydroelectric power (HEP)	A dam floods a huge area behind it, called a reservoir, drowning forest and homes. The dam also blocks the movement of fish.
Settlements	Towns, villages and farms spread as population grows, and the new roads, shops and homes replace the trees.

Threats in South America, Asia and Africa

🌴 Indonesia and Malaysia (Asia)

Large areas of rainforest on the islands of Borneo and Sumatra have been cleared for palm oil plantations. Orangutans lose their habitat as the trees go.

💧 Sarawak, Malaysia (Asia)

The Bakun Dam in Borneo flooded a large area of rainforest. Thousands of people, many of them indigenous, had to move to new homes.

🌳 Congo Basin (Africa)

Logging companies cut roads into the forest, and these roads let farmers and settlers follow. Small farms and logging are major causes of clearance here.

🔥 Madagascar (Africa)

Much of the island's rainforest has been lost to slash-and-burn farming, which clears forest for subsistence crops.

In South America the main threats are cattle ranching, soya farming, mining, roads and HEP schemes. The detailed example of the Amazon in Brazil comes in the lesson on that rainforest.

Environmental impacts of deforestation

Loss of biodiversity: habitats are destroyed, so plants and animals die or move away. Some species live nowhere else and may become extinct.
Soil erosion and loss of nutrients: most nutrients are stored in the trees, not the soil. When the trees go, the leaf litter that feeds the soil stops falling. Without roots and canopy, heavy rain washes the soil away.
River silting: eroded soil is carried into rivers and settles on the bed. The river gets shallower, fish are harmed and the risk of flooding rises.
Less rainfall: trees release water vapour by transpiration. With fewer trees there is less water vapour, so less cloud and less rain locally.
Carbon released: trees store carbon. Burning or rotting trees release carbon dioxide into the air, which adds to climate change. The greenhouse effect is covered in a later lesson.

Social and economic impacts

👥 Indigenous peoples

Indigenous peoples are the original inhabitants of an area. They lose the forest they use for food, medicine, shelter and their way of life, and some are forced to leave.

🦟 Disease

Outsiders bring illnesses such as flu, which indigenous peoples have little protection against. Standing water in cleared land helps mosquitoes breed, so malaria can spread.

💰 Jobs and income

Logging, mining, ranching and plantations create jobs and bring money to a country, which can pay for schools, hospitals and roads.

⚠️ Lost long-term resources

Once the trees are gone, so are timber, nuts, medicines and tourism for the future. The cleared land can soon become poor, so the income does not last.

Impacts at different scales

Scale	Example of an impact
Local	Indigenous people lose their home, and a nearby river is silted up.
Regional	Less rainfall across the area, so crops struggle and rivers have less water.
National	Jobs and export income from timber, palm oil or soya, but the country loses a valuable long-term resource.
Global	Carbon dioxide is released and biodiversity is lost, which affects people everywhere.

Common mistakes

Naming a threat without saying how it causes damage. Always explain the link, for example "roads open up the forest to settlers, so more trees are cleared".
Saying deforestation makes more rain. It means less rain, because there is less transpiration.
Writing only about the environment. Social and economic impacts count too.
Saying all impacts are bad. Jobs and income are real benefits, but they often do not last.

Exam-style question

Fig. 1.1 shows made-up data about one area of tropical rainforest in a country.

Cause of clearance	Share of forest cleared (%)
Cattle ranching	40
Commercial farming	25
Logging	15
Subsistence farming	15
Roads and settlements	5

Fig. 1.1

(a) Identify the main cause of forest clearance shown in Fig. 1.1. [1 mark]

(b) Define the term subsistence farming. [1 mark]

(d) Explain why deforestation causes soil erosion. [4 marks]

(e) Assess the economic and social impacts of deforestation. [6 marks]

Model answer

(a) Cattle ranching (1).

(b) Growing food mainly to feed the farmer's own family (1).

(d) Tree roots hold the soil together (1) and the canopy shelters the ground from heavy rain (1). With the trees gone, rain hits bare soil directly (1) and runoff washes the soil away (1).

(e) Level 3 (5-6 marks): a balanced, developed assessment with a judgement, for example: Economically, logging, mining and plantations create jobs and bring income to the country, for example from palm oil exports. However, the soil is soon exhausted, and long-term resources such as timber, medicines and tourism are lost, so the benefits are short-lived. Socially, indigenous peoples lose their land, food and way of life, and they may catch diseases from outsiders. Overall, the short-term economic gains are outweighed by the lasting social costs and the loss of future income.

Level 2 (3-4 marks): several correct points on economic or social impacts, with some explanation but little balance. Level 1 (1-2 marks): one or two simple points, such as "people get jobs".

Exam tip

In an "Assess" question, weigh the good against the bad and finish with a judgement about which matters more.

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