6.3.1(d) succession

spec points

the process of primary succession in the development of an ecosystem

• to include succession from pioneer species to a climax community

• deflected succession

intro

• Key Concepts:

  • Dynamic Ecosystems: Ecosystems are constantly changing, transitioning from simple to complex structures through succession.

  • Succession: The process of gradual ecological change where biotic (living) and abiotic (non-living) conditions evolve over time.

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  Primary Succession:

  • Occurs on newly formed/exposed land without prior life (e.g., volcanic rock, sand dunes, dried lakes) + gradually colonised by increasing no. of species

  • Stages:

    1. Pioneer Species: First colonizers (e.g., lichens, mosses) survive harsh conditions, break down rock, and create basic soil.

    2. Small Plants: Grasses and shrubs grow in shallow, nutrient-poor soil, further enriching it.

    3. Larger Vegetation: Deeper, nutrient-rich soil supports shrubs, small trees, and eventually large trees.

    4. Climax Community: Stable, self-sustaining ecosystem with dominant species.

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  Environmental Changes During Succession:

  • Species modify the environment, making it more suitable for other species but less hospitable to themselves.

  • E.g., lichens break rock into soil but are replaced by mosses and grasses as soil develops.

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  Secondary Succession:

  • Occurs in previously colonized areas cleared by disturbances (e.g., fires).

  • Starts with existing soil, progressing to a climax community faster than primary succession.

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  Conservation and Management:

  • Deflected Succession: Human activities (e.g., mowing, grazing) prevent succession, halting climax community development.

  • Benefits of Intermediate Stages:

    • Support diverse plant and animal species.

  • Preserve rare or ecologically important species (e.g., pollinators).

  • Conservation involves protection and management of ecosystems

    • In conservation terms, preventing an area from reaching its climax community can sometimes be a good thing

      • This is because ecosystems at the intermediate stages of succession, where small plants, grasses, ferns or shrubs are present, often hold a distinct diversity of plant species (some of which may be of conservation importance) that would no longer exist if the climax community was reached

      • These diverse plant species also provide food and habitat for a high diversity of animal species, some of which may also be of conservation importance (e.g. species that are rare or threatened, or species that have important ecosystem functions, such as pollinators like bees, which are also of great importance to humans due to their role in pollinating the crops we consume)

      • As a result, some conservation projects require the deliberate, artificial prevention of succession in order to preserve an ecosystem in its current stage of succession. For example:

      • Scottish moorlands provide habitats for many species of plants and animals

      • If succession was allowed to occur, this valuable moorland would be replaced by a climax community dominated by spruce forest, which cannot support the same species as the moorlands

      • This would mean losing these important species

      • By having some areas where the climax community is allowed to develop and other areas where succession is prevented so that the moorland remains intact, both ecosystems can be maintained, giving a higher overall species diversity

    • Methods to Prevent Succession:

      • Grazing: Animals eat growing shoots, preventing tree/shrub establishment.

    • Managed Burning: Controlled fires reset succession, maintaining early-stage ecosystems.

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  Examples:

  • Primary Succession: Lichens on volcanic rock gradually form soil, leading to grass, shrub, and tree growth.

  • Managed Moorlands (Scotland): Burning preserves heather and prevents spruce forest, supporting high biodiversity.