# 149 Undesirable effects of deforestation

Deforestation is the removal of large areas of forest to provide land for farming and roads, and to provide timber (wood) for building, furniture and fuel. Deforestation has a number of undesirable effects on the environment.

Deforestation: 

• Reduction of habitats or food sources for animals, which can result in their extinction. Animal and plant diversity is reduced, and food chains are disrupted.

• Loss of plant species and their genes which may be important for medical use or genetic engineering in the future.

• Removal of trees means there are no roots to hold soil, which can result in soil erosion and leaching of minerals. Desertification can eventually occur.

• Lack of roots and soil à flooding and mudslides. Lakes can become silted up.

• Leaching of nutrients into lakes and rivers à eutrophication.

• Less CO₂ is absorbed from the atmosphere, more CO₂ build up à  increase the greenhouse effect.

• Less O₂ is produced à atmospheric O₂ level can drop.

• Less transpiration à reduced rainfall. 

Try this

Figure below show the area of tropical rainforest deforested annually in five different countries, labeled A to E.

1. i) Which of the countries shown has the largest area deforested annually? 

                                                                                                     [1 mark]

   ii) Which of the countries shown has 600 000 hectares of rainforest removed each year?                                                                                     [1 mark]

  iii) In another country, F, 550 000 hectares are deforested annually. Plot this on a copy of the figure.                                                                      [1 mark]

2. i) Country E has a total of 9 000 000 hectares of tropical rainforest remaining. How long will it be before it is all destroyed, if the present rate of deforestation continues?                                                                                    [1 mark]

  ii) Stat 2 reasons why tropical rainforests are being destroyed by humans.

                                                                                                    [2 marks]

  iii) After deforestation has taken place, soil erosion often occurs rapidly. Suggest 2 ways in which this may occur.                                     [2 marks]

3. Tropical rainforests reduce the amount of CO₂ and increase the amount of O₂ in the atmosphere. Explain why both these occurrences are important to living organisms.                                                                      [ 2 marks] 

Answer

1. i) B

  

   ii) A

    iii) Column for F drawn to 550. Column shaded in the same way as the others, and labeled. Column drawn an equal width and distance from the others.

2. i) 30 years

  

   ii) 2 reasons from:

• to clear land for agriculture, housing, industry or roads.
• to collect timber for housing
• to collect timber for fuel.

 iii) 2 suggestions from:

• plants have gone so there are no roots to bind the soil.
• wind blows soil away
• rain washes soil away.

3. Increased CO₂ can lead to global warming, or flooding, or desertification.

O₂: organisms need O₂ for respiration to release energy.