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

Answer 1

The formation of Surtsey, a volcanic island.

Primary succession occurs on newly created or exposed surfaces with no soil or living organisms (e.g., new volcanic islands, lava flows, glacial retreat), so pioneer species (lichens, mosses, etc.) must first build soil before later communities establish. The other disturbances leave soil and biological legacies, so they lead to secondary succession.