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Question

Difficulty: MediumEcological Succession

Arrange the following ecological stages of primary succession on bare rock (xerosere) in correct sequential order from the pioneer stage to the climax community. Which sequence accurately reflects this ecological progression?

  1. 1Crustose lichens colonize the bare rock surface, secreting organic acids that weather the substrate into fine mineral particles.
  2. 2Foliose lichens and mosses establish in rock crevices, trapping wind-blown debris and building a thin organic soil layer.
  3. 3Small herbaceous plants and hardy annual grasses take root, outcompeting mosses and enriching soil humus upon decay.
  4. 4Perennial shrubs and woody bushes colonize, shading out light-demanding grasses and deepening the nutrient-rich topsoil.
  5. 5A mature forest of shade-tolerant canopy trees establishes a stable climax community in equilibrium with the climate.

Answer

The correct succession sequence begins with pioneer crustose lichens, followed by foliose lichens and mosses, then herbaceous grasses, followed by perennial shrubs, and culminates in a climax forest community.
Primary ecological succession on bare rock (xerosere) follows a predictable sequence of seral stages: crustose lichens pioneer soil formation, followed by foliose lichens and mosses deepening soil, herbaceous grasses colonizing, perennial shrubs establishing, and finally mature climax trees reaching ecological equilibrium.

Step-by-Step Solution

1
Identify the pioneer stage on bare substrate.
Crustose lichens colonize bare rock first due to their extreme xerophytic tolerance and ability to weather rock chemically.
Primary succession requires pioneer organisms capable of initiating soil formation on subaerial rock surfaces.
2
Determine the early seral invaders following initial weathering.
Foliose lichens and mosses invade the thin layer of weathered rock particles and organic dust.
Mosses require small amounts of accumulated moisture and organic debris to anchor their rhizoids.
3
Sequence the emergence of vascular herbaceous species.
Annual herbs and grasses establish as soil depth and humus content increase.
Vascular root systems need sufficient soil volume, which accumulates through the decay of mosses and foliose lichens.
4
Identify the transition to woody vegetation.
Perennial shrubs displace grasses due to superior light competition and deeper root structures.
Enriched soil supports larger perennial roots, allowing taller shrub canopy growth.
5
Determine the final equilibrium community.
A mature forest climax community establishes.
Climax trees represent the maximum biomass and biodiversity sustainable under the prevailing climate.

Key Concept

Sequential seral progression in primary lithosere/xerosere ecological succession
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Topics

Ecological Succession

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