Human activity can disrupt ecological succession by removing an existing community, or redirect succession by repeatedly changing the conditions that determine which species survive. The ecosystem may restart at an earlier seral stage, follow a different pathway, or be maintained as a human-controlled community.
This is part of IB ESS subtopic 2.5 Zonation, succession and change in ecosystems. Succession is the replacement of one community by another over time because biotic and abiotic variables change. Each seral community modifies conditions, such as soil depth, nutrient availability, light and moisture, allowing another community to replace it through competition.
Human activity alters this mechanism in several ways:
| Human activity | Effect on succession |
|---|---|
| Deforestation, mining or intensive cultivation | Removes organisms and may degrade or remove soil, resetting succession to an earlier stage. Severe soil removal can initiate conditions similar to primary succession. |
| Fire, grazing or mowing | Repeated disturbance prevents shrubs and trees from becoming established, maintaining grassland or heathland. |
| Abandonment of farmland | Ends disturbance and allows secondary succession from bare or modified soil. |
| Planting, invasive species or pollution | Changes competition and environmental conditions, redirecting succession toward a different community. |
| Restoration and rewilding | Reintroduces species or natural processes, potentially accelerating succession and increasing resilience. |
At HL, a community maintained by human interference rather than progressing toward the expected climax community is called a plagioclimax. In the New Forest, England, livestock grazing helps maintain grassland and heathland that might otherwise develop toward woodland.
A common misconception is that human disturbance always stops succession. It may instead reset, accelerate or redirect it. Management also involves competing perspectives: grazing may protect valued cultural landscapes and livelihoods, while reduced intervention may support rewilding and greater woodland development.
Exam technique: For an explain question, identify the activity, describe how it changes an abiotic or biotic condition, and link this to a change in species competition and the successional pathway. Use “plagioclimax” only for HL and support extended answers with a named example.