Question7 Terrestrial primary ecological succession occurs:Select one alternative: After a small-scale disturbance In an area that was previously occupied by vegetation Where there is bare rock In a tree fall gap ResetMaximum marks: 1 Flag question undefinedSingle choice
A
After a small-scale disturbance
B
In an area that was previously occupied by vegetation
C
Where there is bare rock
D
In a tree fall gap

Question

Question7 Terrestrial primary ecological succession occurs:Select one alternative: After a small-scale disturbance In an area that was previously occupied by vegetation Where there is bare rock In a tree fall gap ResetMaximum marks: 1 Flag question undefinedSingle choice

A

After a small-scale disturbance

B

In an area that was previously occupied by vegetation

C

Where there is bare rock

D

In a tree fall gap

BlackTom AI · Accepted Answer

Primary succession begins on newly exposed substrates such as bare rock, where no soil or prior vegetation exists.

1. Relevant knowledge points and concepts
- Succession: directional change in species composition over time in a community.
- Primary succession: starts on lifeless substrates with no soil (e.g., bare rock, lava flows, glacial till).
- Secondary succession: occurs where soil and some biological legacy remain after a disturbance (e.g., fire, agriculture, tree-fall gaps).
- Pioneer species in primary succession include lichens and mosses that weather rock and begin soil formation; later stages include grasses, shrubs, and eventually trees.

2. Step-by-step reasoning process
- Determine whether the scenario has preexisting soil and vegetation remnants.
- If soil is absent and substrate is bare rock, primary succession is required to build soil from scratch.
- If soil and seed banks remain (disturbance removed vegetation but left soil), then secondary succession occurs.
- Tree-fall gaps and small-scale disturbances occur within an established ecosystem and leave soil and propagules; these are not primary succession.

3. Intermediate reasoning steps (explicit)
- Bare rock → no soil, no seed bank → requires colonization by lichens/microbes → rock weathering and organic matter accumulation → soil formation → successive colonization by vascular plants → primary succession.
- Small disturbance/area previously occupied/ tree-fall gap → soil and seeds present → faster recolonization by existing species → secondary succession.

4. Why the correct answer is correct
- "Where there is bare rock" describes a lifeless substrate lacking soil, which is the defining condition for terrestrial primary ecological succession. The process begins with pioneer organisms that create soil and enable later communities.

5. Why the other options are incorrect
- "After a small-scale disturbance": implies soil and propagules remain → secondary succession.
- "In an area that was previously occupied by vegetation": presence of prior vegetation indicates legacy soil/seed bank → secondary succession.
- "In a tree fall gap": a gap within a forest retains soil and nearby propagules → gap dynamics/secondary succession.

6. Conclusion
Primary succession occurs where there is bare rock. This matches the provided correct answer: Where there is bare rock.

Question7 Terrestrial primary ecological succession occurs:Select one alternative: After a small-scale disturbance In an area that was previously occupied by vegetation Where there is bare rock In a tree fall gap ResetMaximum marks: 1 Flag question undefinedSingle choice

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