Question

Which of the following could result in secondary succession?
the formation of a tall sand dune on a previously grassy beach
a vast glacier in motion forming a U-shaped valley in its wake
a volcanic eruption that covers most of what used to be a forest
an introduced species that destroys all the native plants in an area

Answer 1

Secondary succession occurs after a disturbance removes organisms but leaves the soil (and often seeds/rootstock) intact.

So the ones that could result in secondary succession:
- The formation of a tall sand dune on a previously grassy beach (life/soil was present before)
- An introduced species that destroys all the native plants in an area (plants removed but soil remains)

A glacier scouring a valley and a volcanic eruption covering a forest typically create bare rock or new substrate with no soil, so those lead to primary succession.