Question

which disturbance would result in primary succession?
○ harvesting wheat by using a combine harvester at the end of the growing season
○ controlled burning to stimulate the growth of forest trees such as sequoia
○ the formation of surtsey, a volcanic island off of the southern coast of iceland
○ the effect of a large herd of elephants on the grasses and shrubs in an area

Explanation:

To determine which disturbance leads to primary succession, we recall that primary succession occurs on newly formed or exposed land with no soil or pre - existing organisms.

• Harvesting wheat: This is an agricultural activity on existing soil with a pre - existing ecosystem (the wheat field), so it's secondary succession.
• Controlled burning: It's done on an existing forest ecosystem with soil, so it's secondary succession (stimulates growth in an existing ecosystem).
• Formation of Surtsey: A volcanic island is newly formed, with no soil or pre - existing life initially. So succession here starts from scratch, which is primary succession.
• Elephants' effect on grasses/shrubs: This is a disturbance in an existing grassland/shrubland ecosystem with soil, so it's secondary succession.

Answer:

C. the formation of Surtsey, a volcanic island off of the southern coast of Iceland