Examkin

Question

Difficulty: MediumEcology and Environment

Following the retreat of a glacier, exposed bedrock undergoes primary ecological succession over centuries. In what sequential order do plant communities establish and transition from pioneer species to a stable climax community?

  1. 1Crustose lichens and mosses colonize the bare rock, secreting acids that slowly break down mineral surfaces into the earliest thin layer of soil.
  2. 2Wind-dispersed annual grasses and small flowering weeds germinate in the shallow accumulated soil and organic debris.
  3. 3Fast-growing perennial shrubs and sun-tolerant small trees establish, casting shade and deepening the nutrient-rich topsoil layer.
  4. 4Shade-tolerant, mature hardwood trees reach the upper canopy, forming a stable and self-sustaining climax forest.

Answer

The correct chronological sequence begins with lichens and mosses creating soil on bare rock, followed by annual grasses and weeds, then shrubs and sun-tolerant trees, and concluding with a mature hardwood climax forest canopy.
Primary succession always proceeds from pioneer organisms that build soil on bare rock (lichens and mosses), to opportunist herbaceous species (grasses and weeds), through intermediate woody plants (shrubs and saplings), and culminates in a stable, shade-tolerant climax community (hardwood forest).

Step-by-Step Solution

1
Identify the pioneer community that initiates primary succession on bare, soil-less rock.
Crustose lichens and mosses arrive first to weather the rock and create initial organic substrate.
Primary succession starts in lifeless environments devoid of soil, requiring pioneer species to establish the first soil base.
2
Determine the first herbaceous plants capable of surviving in minimal organic matter.
Annual grasses and small weeds germinate in the newly formed thin soil layer.
These plants have shallow root systems and fast life cycles that further enrich the soil as they decompose.
3
Identify the intermediate woody vegetation that replaces grasses as soil thickens.
Perennial shrubs and sun-tolerant small trees take root.
Deeper topsoil supports larger root systems, and taller shrubs intercept sunlight, shading out lower ground vegetation.
4
Determine the final equilibrium ecosystem stage.
A mature hardwood forest establishes as the stable climax community.
Shade-tolerant seedlings develop under the canopy, maintaining a self-perpetuating ecological balance until a major disturbance occurs.

Key Concept

Primary Ecological Succession
Estimated Time:1m 0s
Rate this question

Topics

Ecology and Environment

More questions from this topic