A-Level Biology: Ecological Succession Explained (Without the Pain)

What is ecological succession?

Succession is the gradual change in species composition of an ecosystem over time. It’s what happens when life slowly moves in, takes hold, and reshapes an environment — sometimes after a disaster, sometimes from bare rock.

For A-Level Biology students, succession isn’t just theory: it links together abiotic factors, biotic interactions, adaptation, competition and nutrient cycling.

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🌋 Primary Succession – Starting from Nothing

Primary succession begins where no soil exists.

Think:

• Bare rock after a volcanic eruption

• Retreating glaciers

• Newly exposed river shingle

Typical stages:

1. Pioneer species (lichens and mosses)

2. Weathering of rock → formation of thin soil

3. Small plants (grasses, herbs)

4. Shrubs

5. Trees → climax community

🔍 Exam tip: Pioneer species must tolerate extreme abiotic conditions — low nutrients, high exposure, little water.

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🌾 Secondary Succession – Life Returns

Secondary succession happens where soil is already present.

Examples:

• Abandoned farmland

• Areas after fire or flooding

• Storm-damaged woodland

Because the soil (and seed bank) already exists, succession is much faster than primary succession.

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🌬️ What Changes During Succession?

Examiners love questions that track trends over time. Students should confidently describe:

Factor	Trend
Biomass	Increases
Species diversity	Increases
Soil depth	Increases
Soil mineral content	Increases
Light at ground level	Decreases
Stability of ecosystem	Increases

This is classic data-handling territory in exams.

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🌳 The Climax Community

The climax community is the final stable ecosystem for a given climate.

In the UK, that’s typically deciduous woodland.

Key idea:

The climax community is dynamic but stable — species populations fluctuate, but the overall structure remains.

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🧪 Required Practical Link

Succession often appears through:

• Sand dune succession

• Rocky shore succession

• Abandoned land studies

Students should be comfortable with:

• Quadrat sampling

• Measuring abiotic factors (light, moisture, soil pH)

• Interpreting kite diagrams and transects

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🧠 Why Students Find Succession Tricky

From years of teaching, common issues include:

• Confusing primary vs secondary succession

• Forgetting why pioneer species are adapted

• Describing stages without linking to abiotic change

The fix? Always tie species change back to environmental conditions.

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✏️ Exam-Ready Takeaway

If a question says “describe and explain succession”, students must:

1. Describe what changes

2. Explain why those changes occur

3. Link to competition, adaptation and environment