Deforestation (AQA GCSE Biology): Revision Note

Deforestation

• Deforestation is the clearing of trees (usually on a large scale)

• If trees are replaced by replanting it can be a sustainable practice

• Unfortunately, this is not often the case and unsustainable deforestation is occurring in many places (forests are being cut down faster than they can regenerate)

• Unsustainable deforestation is occurring on a large scale in the rainforests of tropical areas for various reasons including:

  • to provide more land for farming (e.g. cattle and rice fields)

  • to grow crops from which ethanol-based biofuels can be produced

• As the amount of the Earth’s surface covered by trees decreases, it causes increasingly negative effects on the environment and is a particularly severe example of habitat destruction

• Undesirable effects of deforestation include:

  • extinction of species

  • loss of soil

  • flooding

  • increase of carbon dioxide in the atmosphere

Consequences of deforestation

1. Extinction / loss of biodiversity

   • Forest habitats, especially tropical rainforests, have a huge range of biodiversity and as habitat is destroyed it causes the loss of large numbers of plants and animal species

   • Many of these species are only found in these areas and therefore will become extinct

2. Soil erosion

   • Tree roots help to stabilise the soil, preventing it from being eroded by rain

   • Trees will usually take up nutrients and minerals from the soil through their roots

   • Without trees, nutrients and minerals will remain unused in the soil so will be washed away into rivers and lakes by rain (leaching)

   • This loss of soil nutrients is permanent and makes it very difficult for forest trees to regrow, even if the land is not cultivated with crop plants or grass for cattle

3. Flooding

   • Without trees the topsoil will be loose and unstable so will be easily washed away by rain, increasing the risk of flash flooding and landslides

4. Increased carbon dioxide in atmosphere

   • Trees carry out photosynthesis during which they take in carbon dioxide and release oxygen

   • The removal of significant numbers of trees means less carbon dioxide is being removed from the atmosphere (and less oxygen released)

   • When areas of land in forests are cleared for land use, the trees are often burned as opposed to being cut down. This increases carbon dioxide levels in the atmosphere, contributing to global warming