4.4.5Ecology & the Environment
The Effects of Deforestation — Edexcel International GCSE Biology 4BI1 Revision Notes & Topical Questions
5 min read 4 parts Lesson 7 of 7 Unit quiz
Part 1 of 4What and Why
Deforestation is the large-scale clearing of trees.
Agriculture
- Land is cleared for crops and for cattle, and in some places for rice fields, which provide food and income.
Development
- Trees are also cleared for building, roads, mining and to supply timber and wood products.
Wider cost
- These short-term gains must be balanced against long-term damage to the environment, soils and climate.
Part 2 of 4Effects on Soil and Water
Effects on Soil and Water
Soil erosion
- Without roots and leaf litter to bind the soil, rain and wind wash or blow topsoil away.
Leaching
- Minerals are no longer taken up by tree roots and are washed out of the soil by rain, leaving it less fertile.
Water cycle
- Fewer trees means less transpiration, so less water vapour enters the air, fewer clouds form and local rainfall may fall.
Water pollution
- Eroded soil and leached minerals enter rivers and lakes, which can cause pollution and harm aquatic life.
Part 3 of 4Effects on the Carbon Cycle and Wildlife
Forests are a major store of carbon and a home for a large share of the world's species.
1
Trees remove carbon dioxide from the air by photosynthesis, so clearing them reduces the amount of CO₂ taken in.
2
Burning felled trees releases CO₂ by combustion, and decay by decomposers releases it through respiration.
3
Higher atmospheric CO₂ strengthens the greenhouse effect and contributes to global warming.
4
Loss of the habitat and food sources reduces the number of species, which is a loss of biodiversity, and may lead to extinction.
5
Changes to food webs can follow, since many species depend on forest trees for food and shelter.
Part 4 of 4Exam Checklist & Tips
4.4.5 – Key Points for the Exam
- Deforestation The clearing of trees on a large scale.
- Leaching The washing of dissolved minerals out of the soil by water.
- Soil erosion The removal of topsoil by wind or water.
- Transpiration The loss of water vapour from the leaves of plants.
- Biodiversity The variety of living species in an area.
Common Mistakes
- Saying deforestation has no effect on carbon dioxide;
- fewer trees means less photosynthesis, and burning releases CO₂.
- Forgetting to link fewer trees to less transpiration and so to less rainfall.
- Confusing soil erosion, the loss of soil, with leaching, the loss of dissolved minerals.
- Describing only one effect; exam answers need cause, effect and consequence.
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