Succession

Succession

• the gradual process by which ecosystems change and develop overtime

• it occurs in stages called seral stages

• each stage has a distinct community of organisms

  • change the physical characteristics of the habitat in some way enabling new organisms to become established

Types of succession

• primary succession

  • changes that occur to not previously colonised land

• secondary succession

  • changes that occur to ground that has been previously colonised but then disturbed

Primary succession

• pioneer species

  • eg algae/lichen

  • spores or seeds arrive by wind or are dropped by birds or animals

  • tolerant to extreme conditions

  • able to fix nitrogen

  • can photosynthesise

  • produce many spores or seeds that germinate rapidly

  • decomposition of these species adds organic matter (humus) to the ground

• secondary colonisers

  • eg mosses

  • arrives as spores or seeds

  • weathering of rocks starts to form soil

  • humus adds minerals (nitrates) and the ability to release water

  • decomposition of secondary colonisers adds more humus to the soil that is present

  • some animals may also start to colonise the area as they may feed on pioneer species

• tertiary colonisers

  • eg ferns/herbs

  • waxy cuticle that helps them retain water

  • abiotic factors are improving

• climax community

  • very little change over time

  • a few dominant species present

  • final species depends on climate

    • temperate - large trees

    • sub-arctic - small shrubs

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Deflected succession

• prevents the formation of a climax community

  • forms a plagioclimax community instead

• caused by:

  • mowing

  • farming

  • land clearance (eg burning)

  • grazing and trampling by animals