Ecological Succession

This lesson covers primary and secondary succession, pioneer species, climax communities, and deflected succession, as required by the Edexcel A-Level Biology specification (9BI0), Topic 10 -- Ecosystems.

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What Is Ecological Succession?

Ecological succession is the process by which the structure of a community changes over time in a predictable manner. It involves a series of changes in species composition, diversity, and ecosystem structure, eventually reaching a stable end point called a climax community.

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Primary Succession

Primary succession occurs on land where there has been no previous soil or community -- bare, sterile surfaces such as:

• Newly formed volcanic rock (lava flows)
• Bare rock exposed by glacier retreat
• Sand dunes
• New islands

Stages of Primary Succession

flowchart LR
    A["Bare rock /\nnew surface"] --> B["Pioneer species\ncolonise\n(lichens, mosses)"]
    B --> C["Soil begins to\nform from\nweathered rock +\ndead organic matter"]
    C --> D["Small herbaceous\nplants and grasses\ncolonise"]
    D --> E["Shrubs colonise\nas soil deepens"]
    E --> F["Small trees\nestablish"]
    F --> G["Climax community\n(e.g. mature\noak woodland)"]

1. Pioneer Stage

Pioneer species are the first organisms to colonise a bare surface. They must be tolerant of extreme conditions (exposure, poor nutrients, little water).