Succession

Lecture Content

Introduction

• Succession is the natural, predictable process by which ecosystems change over time.

• It involves the gradual replacement of one community by another until a stable climax community is established.

• Succession explains how barren areas become rich ecosystems and how disturbed habitats recover.

Definition

Ecological succession is the orderly and progressive change in species composition of a community over time, leading to the establishment of a stable ecosystem.

Types of Succession

1. Primary Succession

   • Occurs on bare, lifeless surfaces (no soil initially).

   • Examples: volcanic lava, bare rock, newly formed sand dunes.

   • Pioneer species (lichens, mosses) break down rock → soil formation → grasses → shrubs → trees → climax forest.

2. Secondary Succession

   • Occurs in areas where a community previously existed but was disturbed.

   • Soil is already present.

   • Examples: abandoned farmland, forest after fire, flood‑affected land.

   • Faster than primary succession because soil and seeds remain.

Stages of Succession

1. Nudation

   • Development of bare area due to disturbance (volcano, flood, fire).

2. Invasion

   • Arrival of seeds, spores, or organisms.

3. Competition

   • Species compete for space, nutrients, and light.

4. Reaction

   • Organisms modify the environment (soil enrichment, shade).

5. Stabilization (Climax)

   • A stable, self‑sustaining community forms.

Climax Community

• The final, stable stage of succession.

• Determined by climate and soil.

• Examples:

  • Tropical rainforest in humid regions.

  • Grassland in dry regions.

  • Coniferous forest in cold regions.

Examples of Succession

• Hydrosere: Succession in aquatic habitats (pond → marsh → meadow → forest).

• Xerosere: Succession in dry habitats (bare rock → lichens → moss → forest).

• Lithosere: Succession on rocks.

• Psammosere: Succession on sand dunes.

Importance of Succession

• Restores ecosystems after disturbance.

• Increases biodiversity and stability.

• Improves soil fertility and nutrient cycling.

• Provides habitats for diverse organisms.

• Explains ecological balance and resilience.

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Summary / Key Takeaways

• Succession = natural change in communities over time.

• Two types: primary (bare land) and secondary (disturbed land).

• Stages: nudation → invasion → competition → reaction → climax.

• Climax community depends on climate and soil.

• Succession restores ecosystems, increases biodiversity, and stabilizes environments.