Succession - Ecosystems

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Pioneer VS Climax species/ Primary VS Secondary su

Pioneer species:                                  Climax species:

- e.g. lichens, algae, moss.                   - e.g. bigger plants, woodland.            

- Opportunistic.                                    - Better competitors

- Short lived.                                       -  Long lived.

- Grow rapidly.                                     - Dominant species.

- Unstable.                                          - Stable.

Primary succession:                          

- Plants grow where no plants have grown before.    

Secondary succession:

- Plants grow where there has been a previous population of plants that were destroyed e.g. in a fire.                        

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Succession description and examples

SUCCESSION is a predictable and gradual change in plant and animal communities at a site over time, leading to the development of a climax state. 

  • The first species to colonise are called pioneer species and the ultimate, last species to colonise are called the climax community.
  • Once the climax community has been reached, the succession will not proceed any further, however there will still be changes to the environment.
  • Each next set of colonisers are known as seres
  • Each new community will be better adapted to the changed environment provided by the previous community. 
  • No plants are in bare rock as it is exposed and the heat is reflected/absorbed by the rock. 

Examples of a succession: Psammosere (Sand dune succession):

Pioneer species e.g. sea rocket.

  • These are able to tolerate salt water and unstable sand. 

Climax species reached e.g. woodland.

  • Sand is more stable, increased humus levels and fresh water
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Changes shown through succession over time.

Bare ground:                                                                               

  • No plant competition for light, water, space and nutrients.      
  •  Soil mobile and liable to erosion/loss.                                     
  • More extreme surface microclimate as bare soil absorbs and reflects more heat.                                                    
  • A drier environment, no plant cover to hold moisture above ground and little humus to hold it in the soil.
  • Lower nutrient levels in the soil.      

2 years later:

  • Intense plant competition for space and resources.
  • Soil bound by roots and plant cover.
  • Plant cover provides a certain amount of ground insulation from extremes of temperature - variety of microclimates.
  • Plant cover and increasing humus levels help to retain water.
  • Nutrient levels in the soil will have increased.
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