B42: Biodiversity
Biodiversity, human impacts and conservation
Key Definitions
Biodiversity: The variety of different species of living organisms in an ecosystem, including the variety within each species (genetic diversity) and the variety of different ecosystems.
Deforestation: The permanent removal of trees from an area of forest, often to clear land for agriculture, building or to harvest timber.
Global warming: The long-term increase in the Earth's average surface temperature caused by increased levels of greenhouse gases (primarily CO₂ and methane) in the atmosphere trapping heat.
Conservation: The protection and management of ecosystems and species to maintain biodiversity and prevent extinction.
Sustainable development: Development that meets the needs of the present generation without compromising the ability of future generations to meet their own needs – using resources at a rate that allows them to be replenished naturally.
Deforestation
Deforestation is the large-scale removal of forest. It is a major threat to biodiversity worldwide.
Reasons for Deforestation
- Agriculture – clearing land for cattle ranching and growing crops (e.g. soybeans, palm oil plantations)
- Logging – harvesting valuable hardwood timber for furniture and building
- Urbanisation – expanding towns, cities and roads into forested areas
- Mining – extracting minerals and fossil fuels from beneath forest land
Consequences of Deforestation
| Consequence | Explanation |
|---|---|
| Less CO₂ absorbed | Fewer trees means less photosynthesis, so less CO₂ is removed from the atmosphere. Burning or decomposing felled trees also releases stored CO₂, increasing atmospheric CO₂ levels |
| Habitat loss | Destroying forests removes the habitats of millions of species. Many organisms cannot survive elsewhere and face extinction |
| Soil erosion | Tree roots bind soil together. Without trees, rain washes soil away, leading to barren land, silting up rivers and increased flooding |
| Reduced biodiversity | Tropical rainforests contain over 50% of all species. Destroying them causes mass extinction and reduces global biodiversity |
| Disrupted water cycle | Less transpiration means less rainfall locally, which can turn forest into desert (desertification) |
Example 1: Amazon Deforestation and CO₂
The Amazon rainforest absorbs approximately 2 billion tonnes of CO₂ per year through photosynthesis. Deforestation (approximately 10,000 km² per year in Brazil) not only stops this absorption but also releases carbon stored in the wood. When forest is cleared by burning, the carbon in the trees is released immediately as CO₂ through combustion. This double effect – removing a CO₂ sink and releasing stored carbon – makes deforestation a major contributor to global warming.
Peat Destruction
Peat bogs are wetland areas where partially decomposed plant material has accumulated over thousands of years in acidic, low-oxygen conditions. Peat stores huge amounts of carbon.
Why peat destruction is a problem: Peat is dug up for use as compost in gardens and as fuel in some countries. When peat is exposed to air, decomposers can break it down aerobically, releasing the stored CO₂ back into the atmosphere. This contributes to global warming. Peat bogs also provide unique habitats for rare species such as sundew plants and sphagnum moss – destroying them reduces biodiversity.
Example 2: Peatlands and Carbon Storage
Peatlands cover only 3% of the Earth's land surface but store twice as much carbon as all the world's forests combined. When peat bogs are drained for agriculture or dug up for compost, this carbon is released. The UK has lost approximately 80% of its peatlands, and garden centres are now encouraged to sell peat-free compost alternatives to reduce demand for peat extraction.
Global Warming
Global warming is caused by increasing levels of greenhouse gases in the atmosphere, primarily CO₂ and methane. These gases trap heat that would otherwise escape into space (the greenhouse effect), causing the Earth's average temperature to rise.
| Greenhouse Gas | Sources |
|---|---|
| Carbon dioxide (CO₂) | Burning fossil fuels (coal, oil, gas), deforestation, cement production |
| Methane (CH₄) | Livestock (cows produce methane during digestion), rice paddies, landfill sites, fossil fuel extraction, melting permafrost |
Consequences of Global Warming
- Sea level rise – melting ice caps and glaciers add water to the oceans; warmer water expands (thermal expansion). Low-lying areas and island nations face flooding
- Habitat loss – Arctic ice melting destroys polar bear and penguin habitats; rising sea temperatures bleach and kill coral reefs
- Migration and distribution changes – species move towards the poles or to higher altitudes as temperatures rise; some species cannot migrate fast enough
- Changes in species distribution – some species may become more widespread (e.g. malaria-carrying mosquitoes extending their range), while others decline
- Extreme weather – more frequent and intense droughts, floods and storms
- Biodiversity loss – species unable to adapt or migrate face extinction
Example 3: Coral Bleaching
Coral reefs support around 25% of all marine species. When sea temperatures rise by even 1–2°C above normal, corals expel the algae (zooxanthellae) living in their tissues, causing them to turn white – this is "coral bleaching". Without the algae, corals lose their main food source and often die. The Great Barrier Reef experienced mass bleaching events in 2016, 2017 and 2020 due to record-high sea temperatures. If current warming trends continue, most tropical coral reefs could be lost by 2050.
Pollution
Pollution damages ecosystems and reduces biodiversity in three main ways:
| Pollution Type | Causes | Effects on Biodiversity |
|---|---|---|
| Land pollution | Landfill waste, pesticide and fertiliser use, industrial chemicals, mining waste | Toxic chemicals accumulate in soil; pesticides kill non-target species; heavy metals poison organisms |
| Water pollution | Sewage, fertiliser runoff (nitrates/phosphates), chemical waste, oil spills, plastic waste | Eutrophication (algal blooms deplete oxygen, killing fish and aquatic life); oil coats marine birds and mammals; plastic entangles and is ingested by wildlife |
| Air pollution | Burning fossil fuels (SO₂ causes acid rain), vehicle exhaust, industrial emissions | Acid rain lowers pH of lakes and soil, killing fish and damaging trees; smoke and particulates cause respiratory problems in organisms |
Example 4: Eutrophication from Fertiliser Runoff
When farmers apply excess nitrogen fertiliser, rain washes nitrates into nearby rivers and lakes. This causes algae to grow rapidly (an algal bloom), forming a thick green layer on the water surface. The algae block sunlight, so submerged plants die. When the algae die, decomposers break them down, using up the dissolved oxygen in the water through respiration. Fish and other aquatic organisms suffocate and die. This process – from nutrient enrichment to oxygen depletion – is called eutrophication and it drastically reduces biodiversity in the affected waterway.
Conservation
Conservation aims to protect and maintain biodiversity. Key strategies include:
| Strategy | Description | Example |
|---|---|---|
| Protecting habitats | Preserving natural environments so species can survive in the wild | Designating Sites of Special Scientific Interest (SSSIs) in the UK |
| National parks and nature reserves | Large protected areas where development and exploitation are restricted | Lake District National Park, Serengeti National Park |
| Captive breeding programmes | Breeding endangered species in zoos to maintain population numbers and genetic diversity | Reintroduction of golden lion tamarins to Brazilian Atlantic forest |
| Reintroduction of species | Releasing captive-bred organisms back into their natural habitat | White-tailed eagles reintroduced to Scotland and Ireland |
| Seed banks | Storing seeds of rare and endangered plant species as a genetic resource | Millennium Seed Bank at Kew Gardens stores seeds from over 40,000 species |
| International agreements | Treaties to protect biodiversity and limit harmful activities | CITES (Convention on International Trade in Endangered Species) bans trade in ivory, rhino horn and other products |
Conflicts in conservation: Conservation can conflict with human needs. Local people may need land for farming or firewood. Economic development (building roads, mining) may be restricted by conservation rules. Successful conservation requires balance between protecting biodiversity and supporting local communities through education, alternative livelihoods and sustainable use of resources.
Example 5: Beavers Reintroduced to the UK
Beavers were hunted to extinction in the UK around 400 years ago. Since 2009, they have been reintroduced to several rivers in Scotland, Devon and other areas. Beavers are a keystone species – their dams create wetland habitats that support many other species, improving biodiversity. However, some farmers oppose reintroduction because beaver dams can flood agricultural land. Conservationists must work with farmers to find compromises, such as installing "beaver deceivers" (pipes through dams) that control water levels while allowing beavers to remain.
Sustainable Development
Sustainable development means using resources in a way that allows them to be replenished, so they remain available for future generations. This requires:
- Reducing fossil fuel use and switching to renewable energy (solar, wind, hydroelectric)
- Using resources at a rate that allows natural replenishment (e.g. sustainable fishing quotas, replanting felled trees)
- Recycling and reusing materials to reduce waste and the need for raw material extraction
- Protecting ecosystems while still meeting human needs
Example 6: Sustainable Forestry
In sustainable forestry, only selected mature trees are felled (selective logging) rather than clear-cutting the entire forest. For every tree cut down, a new one is planted. The forest structure and habitats are preserved, allowing biodiversity to be maintained while still providing timber. Certification schemes like the FSC (Forest Stewardship Council) label wood from sustainably managed forests, helping consumers make environmentally responsible choices.
Comparison: Human Impacts on Biodiversity
| Impact | Primary Mechanism | Effect on Biodiversity | Effect on Carbon Cycle |
|---|---|---|---|
| Deforestation | Habitat destruction | Species extinction, reduced variety | Less CO₂ absorbed + stored carbon released |
| Peat destruction | Habitat destruction + compost extraction | Loss of rare peatland species | Massive CO₂ release from stored carbon |
| Global warming | Greenhouse effect from CO₂ and CH₄ | Habitat loss, migration, extinction | Positive feedback (e.g. melting permafrost releases more CH₄) |
| Pollution | Toxic chemicals, eutrophication | Kills organisms, reduces species richness | Less direct impact on carbon cycle |
Practice Questions
Q1: Foundation Define biodiversity and explain why it is important to maintain it.
Q2: Foundation Describe three consequences of deforestation and explain how each reduces biodiversity or contributes to global warming.
Q3: Higher Explain why destroying peat bogs contributes more to global warming than might be expected from their relatively small land area.
Q4: Foundation Describe the greenhouse effect and name two greenhouse gases, stating where each comes from.
Q5: Higher Explain how eutrophication occurs and how it reduces biodiversity in a lake.
Q6: Foundation Describe three conservation strategies and explain why conservation may sometimes conflict with human interests.
Answers
- Biodiversity is the variety of different species living in an ecosystem, including genetic diversity within species and the variety of ecosystems. It is important to maintain because: (1) each species plays a role in the ecosystem (e.g. pollinators are essential for crop production); (2) high biodiversity makes ecosystems more stable and resilient to change; (3) many species provide resources such as medicines (e.g. penicillin from the fungus Penicillium); (4) once a species is extinct, it cannot be recovered and its unique genetic information is lost forever.
- Three consequences of deforestation: (1) Less CO₂ absorbed – fewer trees means less photosynthesis, so less CO₂ is removed from the atmosphere, contributing to global warming. Burning felled trees also releases CO₂. (2) Habitat loss – destroying forests removes the homes of millions of species; many cannot survive elsewhere and face extinction, directly reducing biodiversity. (3) Soil erosion – without tree roots to bind the soil, rain washes it away, making the land barren so organisms that lived in the soil or depended on plants growing in it also lose their habitat, further reducing biodiversity.
- Peat bogs cover only about 3% of the Earth's land surface but store approximately twice as much carbon as all the world's forests combined. This is because peat is formed from partially decomposed plant material that has accumulated over thousands of years in acidic, low-oxygen (anaerobic) conditions that prevent complete decomposition. When peat bogs are drained or dug up, the peat is exposed to oxygen and aerobic decomposers break it down rapidly, releasing the stored carbon as CO₂. Additionally, when peat is dried and burned as fuel, all its stored carbon is released immediately through combustion. This enormous release of stored carbon from a relatively small area makes peat destruction disproportionately harmful to the climate.
- The greenhouse effect occurs when greenhouse gases in the atmosphere trap heat that would otherwise escape into space. Sunlight passes through the atmosphere and warms the Earth's surface. The Earth radiates heat back as infrared radiation. Greenhouse gases (CO₂, methane, water vapour) absorb this infrared radiation and re-radiate it in all directions, including back towards the Earth's surface, warming it further. Two key greenhouse gases: (1) Carbon dioxide (CO₂) – released by burning fossil fuels, deforestation and cement production. (2) Methane (CH₄) – released by livestock digestion, rice paddies, landfill waste, and fossil fuel extraction. Methane is approximately 80 times more potent as a greenhouse gas than CO₂ over a 20-year period.
- Eutrophication occurs when excess nutrients (especially nitrates and phosphates from agricultural fertilisers) are washed into a lake by rain. The nutrients cause algae to grow rapidly, forming a thick green bloom on the water surface. The algal bloom blocks sunlight, so submerged plants cannot photosynthesise and die. When the algae and dead plants are broken down by decomposers (bacteria), the bacteria respire and use up the dissolved oxygen in the water. This creates anoxic (low oxygen) conditions that kill fish, insects and other aquatic organisms. Biodiversity is reduced because only organisms tolerant of low oxygen can survive, while most species die. The lake ecosystem collapses, leaving only a few pollution-tolerant species.
- Three conservation strategies: (1) Captive breeding programmes – breeding endangered species in controlled environments (zoos) to maintain population numbers and genetic diversity, with the aim of eventual reintroduction to the wild. (2) National parks and nature reserves – large protected areas where development, hunting and resource extraction are restricted to preserve habitats and the species that depend on them. (3) Reintroduction of species – releasing captive-bred organisms back into their natural habitats to re-establish wild populations that had been lost locally. Conservation can conflict with human interests because: local people may need land for farming or building; restricting fishing or logging in protected areas reduces income for local communities; reintroduced predators (e.g. wolves) may threaten livestock; and economic development may be limited by conservation regulations. Successful conservation requires working with local communities to find sustainable compromises.
Exam Tips
- When asked about deforestation, always mention both the biodiversity impact (habitat loss) and the carbon cycle impact (less CO₂ absorbed + stored carbon released)
- For peat destruction questions, emphasise that peat stores huge amounts of carbon in a small area – this is what makes it disproportionately damaging
- When describing the greenhouse effect, explain the mechanism (sunlight in, infrared trapped), don't just say "gases trap heat"
- In eutrophication questions, follow the sequence: fertiliser runoff → algal bloom → light blocked → plants die → decomposers use oxygen → fish die. Missing a step loses marks
- For conservation questions, always mention the conflict between conservation and human needs – this shows balanced, higher-level thinking
- Use the term sustainable development correctly – it means meeting present needs without preventing future generations from meeting theirs
🔢 Maths Skills
Mathematical Skills
Interpreting biodiversity index data: Simpson's Index of Diversity = 1 − Σ(n/N)², where n = number of individuals of each species and N = total number of individuals. A higher value (closer to 1) indicates greater biodiversity. For example, if Area A has an index of 0.85 and Area B has 0.62, Area A has higher biodiversity.
Calculating percentage deforestation: if forest area decreased from 4,100,000 km² to 3,300,000 km², the percentage loss = (4,100,000 − 3,300,000) / 4,100,000 × 100 = 19.5%.
⚠️ Common Misconceptions
Watch Out!
Students often think biodiversity means only the number of species. Wrong: Biodiversity = number of species only Correct: Biodiversity includes species diversity, genetic diversity within species, and ecosystem diversity
Students often think human activity always reduces biodiversity. Wrong: Human activity always reduces biodiversity Correct: Some human management (e.g. creating nature reserves, controlled burning, sustainable forestry) can increase or maintain biodiversity
✍️ 6-Mark Question
Extended Answer
6 marks: Explain why biodiversity matters and evaluate the impact of deforestation on biodiversity and the carbon cycle.
Biodiversity matters because: each species plays a role in the ecosystem (e.g. pollinators are essential for crop production); high biodiversity makes ecosystems more stable and resilient to change; many species provide resources such as medicines; once a species is extinct its unique genetic information is lost forever. Deforestation reduces biodiversity by destroying habitats — tropical rainforests contain over 50% of all species. It also affects the carbon cycle: fewer trees means less CO&sub2; is removed by photosynthesis; burning or decomposing felled trees releases stored CO&sub2;; this contributes to global warming, which further threatens biodiversity through habitat loss (e.g. coral bleaching) and species migration. Deforestation also causes soil erosion and disrupts the water cycle through reduced transpiration.
Mark scheme: Up to 3 marks for why biodiversity matters, up to 3 marks for evaluating deforestation impact on both biodiversity and carbon cycle
📊 AO3: Analyse & Evaluate
Analysis and Evaluation
Area X is a nature reserve with Simpson's Index of 0.91. Area Y is intensively farmed land with an index of 0.35. A proposal suggests converting 20% of Area X into farmland to increase food production. Evaluate this proposal, considering both biodiversity and food security. What alternative approaches could achieve food security without reducing the reserve?
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