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Succession is the process by which communities colonise an ecosystem and are then replaced over time by other communities:

Succession is the process

Pioneer species: These are the first species to occupy a new habitat, starting new communities. They have rapid reproductive strategies, enabling them to quickly occupy an uninhabited area. Many have an asexual stage to their reproduction.

Seres: These are the various stages that follow on from the pioneer species.

Climax community: This is the stable community that is reached, beyond which, no further succession occurs.

Primary succession

This occurs when the starting point is a bare ecosystem, (e.g, following a volcanic eruption or a landslide). The pioneer species are usually lichen, moss or algae. They are able to penetrate the bare surface, trap organic material and begin to form humus.

Over several generations soil begins to form. The soil can be used by a more diverse range of plants with deeper root systems. Gradually larger and larger plants occupy the ecosystem along with a diversity of animals.

Finally a climax community is reached and the species present do not change unless the environment changes in some way.

An example of primary succession forming an oak woodland:

  1. Bare rock is colonised by mosses and lichen.
  2. Small plants, ferns and grasses take over.
  3. Larger plants with deeper roots appear.
  4. Bushes and shrubs replace non-woody plants.
  5. Fast growing trees form a dense, low wood.
  6. Larger, slow growing oak trees create the oak woodland.

Secondary succession

This occurs when the starting point is bare, existing soil, (e.g, following a fire, flood or human intervention). This type of succession proceeds in the same way as primary succession except that the pioneer species tend to be grasses and fast growing plants.

An example of secondary succession forming an oak woodland:

  1. Bare soil is colonised by grasses and pioneer plants.
  2. Grasses begin to predominate with time.
  3. Shrubs replace the grasses.
  4. Fast growing trees appear.
  5. Slow growing oaks create the climax community.