🏗 Building
Houses, roads, shops and factories cover the ground. Plants cannot grow under concrete, and the animals that depend on them have to move or die out.
Biodiversity and Human Impact » Land Use, Deforestation and Global Warming
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.7.3.3, 4.7.3.4, 4.7.3.5
- How building, quarrying, farming and dumping waste take land from other species
- Why destroying peat bogs reduces biodiversity and adds carbon dioxide to the air
- Why tropical forests are cleared, and what that costs the environment
- How carbon dioxide and methane contribute to global warming, and what it does to living things
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Unlock This CourseHumans take up land
Every species needs somewhere to live. The more land people use, the less is left for wild plants and animals. Humans reduce the amount of land available for other species in four main ways:
⛏ Quarrying
Digging out stone, sand and clay removes whole areas of habitat and leaves a large hole in the ground.
🌾 Farming
Fields of one crop replace woodland, meadow and wetland. A single crop supports far fewer species than the habitat it replaced.
🗑 Dumping waste
Land used to bury or pile up waste cannot be used by wildlife.
The result is that habitats shrink, so fewer species can live there. This is how human land use lowers biodiversity.
Peat bogs
A peat bog is a wet habitat where plant material has built up over a very long time. Because the ground is waterlogged, the dead plants do not fully decay. They pile up as a dark, spongy material called peat.
Peat bogs are home to a special variety of plants, animals and microorganisms. People dig up peat and use it to make garden compost.
Key terms:
- Peat: partly decayed plant material that builds up in waterlogged areas such as bogs.
Destroying peat bogs causes two problems:
- Less habitat, less biodiversity. The bog area gets smaller, so the variety of plant, animal and microorganism species that live there falls.
- More carbon dioxide. When peat decays or is burned, it releases carbon dioxide into the atmosphere.
A conflict to weigh up
Gardeners and farmers want cheap, plentiful compost, and that helps to grow more food. But peat bogs are valuable habitats, and protecting them also helps to cut carbon dioxide emissions. In an exam you may be asked to weigh up these two sides. A good answer gives a point for each side and then reaches a conclusion.
Large-scale deforestation
Deforestation means clearing forest on a large scale. In tropical areas, large areas of forest have been cleared for two main reasons:
- to provide land for cattle and for rice fields
- to grow crops for biofuels
Cleared land does give people farmland and fuel crops. But the forest is lost, and so are the many species that lived in it.
Key terms:
- Deforestation: the large-scale clearing of forest.
- Biofuel: a fuel made from plants or other living material.
🌳 Fewer trees
Trees take in carbon dioxide for photosynthesis. With fewer trees, less carbon dioxide is removed from the air.
🔥 Burning and decay
Felled trees are often burned or left to rot. Both release carbon dioxide into the atmosphere.
When you are asked to evaluate the environmental implications of deforestation, think about both sides: the benefit of new farmland or fuel, against the loss of habitat, the loss of species and the extra carbon dioxide.
Global warming
The levels of carbon dioxide and methane in the atmosphere are increasing, and they contribute to global warming.
Key terms:
- Global warming: the increase in the average temperature of the Earth's surface.
Look back over this lesson. Peat decaying or burning, and forest being cleared and burned, release carbon dioxide into the air.
Biological consequences of global warming
You should be able to describe some of the biological consequences of global warming. Here are three:
❄ Loss of habitat
Warmer temperatures melt polar ice, so species that live on or near the ice lose their habitat.
🗺 Changed distribution
As the temperature rises, some species move to cooler places. Species that cannot move may die out.
🐦 Changed migration
The timing and routes of animal migrations can change as the seasons shift.
How do we know? Scientific consensus
Climate is a very complex system, so some evidence is uncertain or incomplete. For example, it is hard to say exactly how much the temperature will rise or exactly how a species will respond.
Even so, scientists agree that global warming is happening. This agreement is called a scientific consensus. It is based on systematic reviews of thousands of peer reviewed publications. Peer review means other scientists check the work before it is published. A view backed by that much checked evidence is far stronger than a single study or an opinion.
Common mistakes
1. Forgetting where the extra carbon dioxide comes from. Trees take in carbon dioxide by photosynthesis; the extra carbon dioxide from deforestation comes from felled wood being burned or decaying.
2. Writing only "pollution" in an answer about peat. Name the gas: carbon dioxide is released when peat decays or is burned.
3. Forgetting that methane is a second gas. Both carbon dioxide and methane contribute to global warming.
Exam-style question
(a) Give two ways in which humans reduce the amount of land available for other species. [2 marks]
(b) Peat bogs are dug up to make garden compost. Explain how this affects biodiversity and the atmosphere. [3 marks]
(c) Describe one biological consequence of global warming. [1 mark]
Model answer
(a) Any two from: building (1), quarrying (1), farming (1), dumping waste (1).
(b) The bog habitat gets smaller (1), so the variety of plant, animal and microorganism species that live there falls (1). When the peat decays or is burned, carbon dioxide is released into the atmosphere (1).
(c) Any one from: polar ice melts so species lose their habitat; species move to cooler places so their distribution changes; migration patterns change (1).
Exam tip
In part (b) the word "explain" and the 3 marks tell you to give two points about biodiversity and one about the atmosphere. Name the gas, carbon dioxide, rather than just saying "pollution".