Primary succession begins on newly formed substratum with no soil or pre-existing community. Secondary succession begins after disturbance where soil remains, so recovery is usually faster.
This is core SL and HL content in IB ESS subtopic 2.5 Zonation, succession and change in ecosystems.
How the Processes Differ
Succession is replacement of one community by another over time as biotic and abiotic conditions change. Each stage is a seral community whose organisms modify conditions for later communities.
| Feature | Primary succession | Secondary succession |
|---|---|---|
| Starting conditions | Newly formed surface without soil or a previous community | Previously inhabited area where soil remains |
| Typical cause | Volcanic lava, exposed rock after glacial retreat | Fire, abandoned agriculture, storms or forest clearance |
| Pioneer community | Lichens and mosses tolerant of severe conditions | Grasses, herbs and plants growing from seeds, roots or survivors |
| Soil | Must develop through weathering and organic matter accumulation | Already present, often with nutrients, microorganisms and a seed bank |
| Relative speed | Usually slower | Usually faster because soil and biological storages remain |
| Named example | Surtsey, Iceland | 1988 Yellowstone fires, USA |
In primary succession, pioneer organisms weather rock and add dead organic matter. Soil depth, nutrient cycling, biomass and diversity generally increase.
In secondary succession, surviving soil stores nutrients, seeds and microorganisms. This increases ecosystem resilience and shortens the time lag before vegetation becomes established.
A common misconception is that every disturbance causes primary succession. The decisive factor is not disturbance size but whether soil and evidence of the previous community remain.
Human decisions influence recovery. Replanting, farming or natural regeneration reflects economic priorities, conservation perspectives and affected communities' needs.
Exam Technique
For a distinguish question, refer to both processes throughout and make soil availability the central contrast. For an explain question, link soil, nutrients, seeds and microorganisms to faster secondary succession.