Ecological Succession Overview

Ecological Succession

• Gradual change in species composition and community processes over time is called ecological succession.
• Understanding succession is crucial for ecosystem management.
• Succession is categorized by timescale:
  • Paleoecological changes (millions of years)
  • Medium timescale changes (1-1000 years)
• Alternatively, succession is classified as:
  • Primary succession: Begins in bare land with no prior life.
  • Secondary succession: Occurs in areas where a prior ecosystem was damaged, either partially or fully, by natural or unnatural causes.

Primary Succession

• Begins on bare rock or other initially lifeless surfaces.
• Soil formation is a slow process, initiated by pioneer species (e.g., lichens, mosses).
• Pioneer species break down rock and create initial soil.
• Gradually, soil becomes fertile enough for other plants (herbs, grasses, low shrubs).
• Eventually, trees establish, replacing shrubs over hundreds to thousands of years.

Secondary Succession

• Occurs in areas where a previous ecosystem was damaged (e.g., by fire, flood, human activity).
• Soil already exists, so the process is generally faster (5-10 times) than primary succession.
• Existing nutrients in the soil facilitate faster re-growth.
• Climax species eventually dominate the area.

Stages of Succession

• Nudation: Formation of bare ground due to factors like volcanic eruptions, landslides, or natural disasters.
• Invasion: Arrival of pioneer organisms and establishment of initial populations.
• Competition: Increased competition for resources as populations grow. Intraspecific (within a species) and interspecific (between species) competition result in modifications to the environment that may lead to replacement of existing species by new ones. Co-action and co-existence also occur at one point.
• Climax: Final stage where a relatively stable community (climax community) is established; further change occurs only through significant disturbances.

Other Types of Succession

• Hydrosere: Succession in wet habitats, starting with submerged plants like Elodea and Hydrilla.
• Xerosere: Succession in dry habitats, starting with algae and lichens (e.g., Rhizocarpon, Rhinodina).
• Lithosere: Succession starting on bare rock.
• Halosere: Succession in saline environments.

Hydrosere vs. Xerosere

• Hydrosere: Starts in wet habitats; progression through submerged, floating, reed swamp, woodland stages to climax forest.
• Xerosere: Starts in dry habitats; progression through lichen, moss, herb, shrub, and climax forest stages.