Question

Explain the ecological succession on a bare rock formed by volcanic activity.

Answer 1

Succession on a bare rock formed by volcanic activity is primary succession, which begins where no community existed before. It is a xerarch succession (dry habitat) and may take about 1000 years or more to reach climax.

Stages (sequence):

1. Pioneer stage: Lichens (fungus and algae) colonise the rock. They secrete acids that chemically weather the rock and form the first thin soil.
2. Moss stage: Mosses grow in clumps and trap wind-blown particles, adding organic matter and increasing soil depth.
3. Herb and grass stage: Ferns, grasses and small herbs establish on the accumulating soil.
4. Shrub stage: Shrubs replace herbs as the soil becomes deeper and richer in nutrients and moisture.
5. Forest (climax) stage: Trees and large seed-bearing plants form a stable, self-sustaining community.

Sequence: Bare rock → Lichens → Mosses → Herbs and grasses → Shrubs → Trees (Climax)

Key points:

• Each stage modifies the environment and makes it suitable for the next stage.
• Pioneer species have high growth rates and short life spans.
• The climax community has high biomass, many species and dominant trees.

Lichens begin soil formation, and gradual changes in soil and climate lead to a stable forest community.