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Question

Difficulty: EasyEcological Succession

Which of the following represents the correct sequential order of plant community stages during primary ecological succession on a bare rock surface (xerosere), from initial colonizers to the mature climax community?

  1. 1Crustose lichens colonizing bare rock
  2. 2Foliose lichens and mosses growing in thin soil pockets
  3. 3Herbaceous grasses and shallow-rooted weeds
  4. 4Climax forest of mature hardwood trees

Answer

The correct sequence of primary succession on bare rock is: Crustose lichens → Foliose lichens and mosses → Herbaceous grasses and weeds → Climax forest.
Primary succession on bare rock begins with crustose lichens breaking down rock surfaces. Decomposing lichen material forms a thin soil layer that allows mosses and foliose lichens to colonize. As soil accumulates further, herbaceous grasses establish, eventually yielding to a stable climax forest community.

Step-by-Step Solution

1
Identify the pioneer community
Crustose lichens are the first organisms capable of colonizing bare rock substrate where soil is entirely absent.
Pioneer species in primary succession must tolerate extreme exposure and contribute to initial weathering of substrate.
2
Arrange the intermediate seral stages by soil depth requirement
Mosses and foliose lichens establish next, followed by herbaceous grasses as organic matter builds up.
Bryophytes require minimal soil pockets, whereas herbaceous plants need shallow organic topsoil to anchor root systems.
3
Identify the stable terminal community
The progression culminates in a mature climax forest.
The climax community represents the final, self-perpetuating stage in equilibrium with the prevailing climate.

Key Concept

Sequential Seral Stages of Primary Ecological Succession (Xerosere)
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Topics

Ecological Succession

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