Example 1
Vegetation returns to a burnt grassland where soil remains. Classify the succession.
Secondary succession: the disturbance removed vegetation but did not remove the soil.
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Year 11 · SACE Stage 1
Succession and ecosystem change
Distinguish primary and secondary succession and read changes over time.
Method and worked examples
Ecological succession is change in community composition and associated conditions over time. Primary succession begins where soil is initially absent, such as newly exposed rock. Secondary succession occurs after a disturbance where soil remains. Early colonisers can alter shade, organic matter and substrate conditions, affecting later species. Pathways depend on the setting and disturbance history; there is no single sequence for every ecosystem.
Biotic and abiotic changes influence one another. A decline in light at ground level can accompany canopy development, changing which plants establish. Fossils and sediments provide evidence of longer-term environmental changes. Marine fossils in a rock layer support a past marine setting, but one finding does not provide an exact past temperature. Interpret the stated evidence at the level it supports.
Example 1
Example 2
A sequence shows bare rock, lichens, shallow soil and later grasses. Identify one relevant change.
Soil development changes the substrate and permits establishment of plants requiring soil.
Watch out: Succession depends on available species, conditions and disturbances, so trajectories can differ.