Biological Succession- Secondary School Guide
What Is Biological Succession?
biological succession is the process where an ecosystem changes over time. It moves from bare, lifeless ground to a thriving community of plants and animals. This doesn't happen overnight. It takes decades, sometimes centuries.
The basic idea: disturbed or newly formed land gets colonized by living organisms. These organisms change the environment, making it suitable for other species. The process continues until a stable community forms.
Primary Succession
Primary succession starts on completely barren ground. No soil exists. Nothing has ever lived there.
Examples:
- Volcanic rock after an eruption
- Sand dunes
- Newly formed islands
The first colonizers are always pioneer species like lichens and mosses. They break down rock into tiny particles. Dead organic matter builds up. Eventually, soil forms.
This is slow. It can take thousands of years before a stable ecosystem develops.
Secondary Succession
Secondary succession starts where life already existed. Soil is present. Some organisms survived.
Examples:
- Abandoned farmland
- Forest after a wildfire
- Cleared land after logging
This is faster than primary succession because the soil already contains seeds, roots, and nutrients. Recovery takes years to decades, not millennia.
Stages of Succession
Succession follows a predictable pattern:
1. Pioneer Stage
Lichens and mosses colonize bare rock or sand. They trap moisture and add organic material. No soil exists yet.
2. Early Colonizers
Small plants like grasses take hold. They have shallow roots that hold soil together. Insects and spiders move in.
3. Intermediate Stage
Shrubs and small trees appear. The soil gets deeper and richer. Birds and small mammals arrive.
4. Climax Community
A stable community forms. The same species dominate year after year. This is the final stage—unless another disturbance resets everything.
Climax Community Explained
The climax community is the end point of succession. It's the ecosystem that remains stable until something disrupts it.
In the UK, this might be oak woodland. In tropical areas, it's rainforest. In grasslands, it's... well, grassland maintained by grazing or fire.
Here's the honest truth: climax communities are rare in nature. Most ecosystems get disturbed regularly. Fire, flooding, human activity—these reset succession constantly.
Primary vs Secondary Succession: The Key Differences
| Feature | Primary Succession | Secondary Succession |
|---|---|---|
| Starting point | Completely barren ground | Previously inhabited area |
| Soil presence | No soil initially | Soil already exists |
| Speed | Very slow (1000s of years) | Faster (decades to centuries) |
| Pioneer species | Lichens, mosses | Grasses, herbaceous plants |
| Examples | Volcanic islands, sand dunes | Burnt forest, abandoned fields |
Natural vs Human-Caused Succession
Natural disturbances like lightning strikes, floods, and landslides trigger succession. These are part of how ecosystems renew themselves.
Human activities also cause succession. Deforestation, agriculture, and urban development create new starting points for succession.
The difference? Natural disturbances usually allow faster recovery because the soil ecosystem remains largely intact. Human disturbance often degrades soil, removing nutrients and beneficial organisms.
How to Remember This for Exams
Forget memorizing everything. Focus on understanding the core sequence:
- Bare ground → pioneer species arrive
- Pioneer species → create soil
- Soil → larger plants grow
- Larger plants → more animals arrive
- Stable community → climax reached
For any example question, ask yourself: is soil present? If yes, it's secondary succession. If no, it's primary.
Getting Started: Answering Succession Questions
When you encounter a question about succession, work through this checklist:
- Identify if the area had soil before (secondary) or started completely bare (primary)
- List what's currently present—pioneer species or established vegetation?
- Describe what will change next and why
- Name the climax community for that environment
Example: "A volcanic eruption destroyed an island. Lichens are now growing on the bare rock. Describe how the ecosystem will develop over time."
Your answer: Lichens will break down rock and form soil. Grasses and small plants will colonize. Shrubs and trees will follow. Eventually, a climax community of woodland will form. This is primary succession because soil didn't exist before.
Why Succession Matters
Succession explains why disturbed areas recover. It shows how ecosystems repair themselves after damage. Understanding this helps ecologists predict how habitats will respond to conservation efforts or environmental disasters.
It also explains why old-growth forests are rare. Most ecosystems experience regular disturbances that prevent them from reaching climax stage.