Secondary succession is a process of ecosystem recovery that occurs in areas where a community has been disturbed but the soil and nutrients remain intact.
Defining Secondary Succession
Based on ecological principles, secondary succession happens when a climax community or intermediate community is impacted by a disturbance. Unlike primary succession, which starts from bare rock, secondary succession takes place in an environment that previously supported life.
This process essentially restarts the cycle of succession, allowing a new series of communities to develop over time. However, it's crucial to note that this restart is not back to the beginning—soil and nutrients are still present. This pre-existing foundation significantly speeds up the recovery process compared to primary succession.
How it Happens: The Role of Disturbance
Secondary succession is triggered by various types of disturbances that alter an existing ecosystem but do not remove the soil. These disturbances can be natural or human-caused.
Examples of disturbances include:
- Wildfires: Burning vegetation clears land but often leaves soil relatively undamaged.
- Floods: Can devastate plant life but deposit nutrient-rich sediment.
- Logging or Deforestation: Removal of trees while soil structure largely remains.
- Abandonment of Agricultural Land: Allows nature to reclaim cultivated areas.
- Hurricanes or Windstorms: Can uproot trees and change forest structure.
- Disease or Pest Outbreaks: Killing off dominant species in a community.
Key Difference: Why Soil Matters
The presence of pre-existing soil and nutrients is the defining characteristic of secondary succession. This is the main reason it differs fundamentally from primary succession.
| Feature | Primary Succession | Secondary Succession |
|---|---|---|
| Starting Point | Bare rock, no soil | Existing soil/nutrients, disturbed area |
| Previous Life | None | Present (removed by disturbance) |
| Pioneer Species | Lichens, mosses (create soil) | Grasses, weeds, fast-growing plants |
| Time Scale | Very long | Shorter |
| Cause | Volcanic eruption, glacial retreat | Fire, flood, logging, abandonment |
Because soil is already present, pioneer species in secondary succession don't need to break down rock or create soil from scratch. Instead, they are typically fast-growing plants like grasses and weeds that can quickly colonize the disturbed area. This allows the ecosystem to recover and progress through different stages much more rapidly.
The Process
Following a disturbance, the exposed area is quickly colonized by pioneer species. These are then gradually replaced by other plant communities—such as shrubs and then different types of trees—in a predictable sequence. This progression continues over time, moving towards a community structure that is stable for that environment, often referred to as a climax community, before another disturbance potentially initiates the cycle again.
Examples in Nature
- A forest area regrowing after a wildfire.
- An abandoned farm field slowly being taken over by native plants.
- A clear-cut forest section where new trees begin to sprout from existing soil.
In each of these scenarios, the soil remains, providing a foundation for rapid recolonization and recovery.
