Ecological succession and primary successionSpec D4.2.12, D4.2.13
In short
Ecological succession is the sequence of changes in a community over time. It can be triggered by changes in both the abiotic environment and biotic factors. During primary succession on new land, such as sand dunes, the size of plants, primary production, species diversity, complexity of food webs and nutrient cycling all increase.
Ecological succession is a sequence of changes in the community of an area over time. It can be triggered by changes in the abiotic environment, for example new land exposed by a retreating glacier or deposited as sand dunes, and by biotic factors, for example organisms forming soil, casting shade or adding nitrogen, so that conditions suit different species.
Primary succession starts on land with no soil. Secondary succession starts where soil remains after a disturbance, such as a fire.
Example: sand dune succession
- Pioneer species such as sand couch grass tolerate salt spray and wind and colonise bare sand above the high-tide line.
- Their roots trap sand; marram grass grows up through new sand and stabilises taller dunes.
- Dead plant matter adds humus, so the soil holds more water and nutrients; mosses, lichens and many herbs colonise.
- Shrubs such as gorse and sea buckthorn grow in the deeper soil and shade out low plants.
- Woodland of trees such as birch, pine and oak develops.
| Feature | Change |
|---|---|
| Size of plants | Increases, from low pioneers to shrubs and trees |
| Amount of primary production | Increases |
| Species diversity | Increases |
| Complexity of food webs | Increases, with more trophic links |
| Amount of nutrient cycling | Increases, as more organic matter is decomposed and soil deepens |
(opens full size in a new tab)Written and checked against the IB Biology HL specification · Updated October 2026