Succession - Ecosystems

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.                        

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. 

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.