Ecological succession is directional community change over time after new habitat forms or disturbance resets an existing ecosystem with remaining resources.
Ecological succession is an orderly change in community composition through time, triggered by changes in abiotic conditions, biotic interactions, or both.
Pioneer organisms modify light, soil, nutrients and moisture; competition, facilitation, herbivory and dispersal then change which species can establish next.
In an abandoned quarry, lichens and mosses alter bare substrate and add organic matter, allowing grasses, shrubs and later woodland species to colonize.
Succession has a directional mechanism but not one universal fixed sequence; climate, starting conditions and disturbance can redirect it.
This objective is assessed through structured response, commonly using State / Distinguish / Suggest.
State / Distinguish / Suggest
Build the answer around this relationship: Succession describes changes in organism communities through time.
Representative question
Distinguish between primary succession and secondary succession, giving an example of each.
primary succession
secondary succession
on newly formed land
previously occupied land;
eg volcano
eg after forest fire;
no organic content
soil with organic content;
no organisms present at start
organism may be present at start;
slower/longer process
quicker process;
To award [3] an example must be provided.
A table format is not necessary.
HL D4.2 is the long-term change story. Succession begins after new habitat or disturbance, pioneer species modify conditions, primary succession builds soil and complexity, and some systems repeat cycles or are held before climax by disturbance.
HL succession questions focus on community pathways over time. The answer starts from the initial condition, shows how species modify abiotic conditions and interactions, and identifies whether the pathway is primary, cyclical, climax, or arrested by repeated disturbance.