Question

which of the following is an example of primary succession? choose 2 answers: a an abandoned agricultural field gradually becomes a forest again as shrubs and trees grow back. b flooding from a hurricane recedes on a barrier island and grasses and sedges grow back. c lava flows cool after a volcanic eruption and lichens start to grow. d a glacier melts, leaving behind bare rocks on which mosses begin growing.

Explanation:

To determine examples of primary succession, we recall that primary succession occurs on newly formed or exposed land with no prior soil or organic matter.

• Option A: An abandoned agricultural field has existing soil (from previous farming), so this is secondary succession (succession on disturbed land with soil).
• Option B: The barrier island after hurricane flooding still has soil (since it was a pre - existing island), so this is secondary succession (recovery of a disturbed ecosystem with soil).
• Option C: After a volcanic eruption, lava cools to form new rock with no soil. Lichens (pioneer species) starting to grow here is primary succession as they colonize a newly formed, lifeless substrate.
• Option D: When a glacier melts, it leaves bare rocks with no soil. Mosses (pioneer species) beginning to grow on these bare rocks is primary succession as they are colonizing a newly exposed, soil - less area.

Answer:

C. Lava flows cool after a volcanic eruption and lichens start to grow.
D. A glacier melts, leaving behind bare rocks on which mosses begin growing.