Question

Determine whether the following disturbances will be followed by primary or secondary succession.

In coastal areas, wind moves sand, blowing away or engulfing the soil, and eventually creating sand dunes:

The introduction of livestock to an area leads to over-grazing that removes native grasses:

A forest is cleared to gather lumber used for building houses:

A lava flow down the side of a volcano destroys all vegetation and eventually turns into volcanic rock when it cools and hardens:

Answer 1

1. Primary succession — sand dunes form new, soil-free substrate where pioneer species must colonize.
2. Secondary succession — overgrazing removes vegetation but leaves soil (and often seeds/rootstock), so regrowth follows on existing soil.
3. Secondary succession — logging removes the plants but leaves the soil intact, allowing succession to proceed.
4. Primary succession — cooled lava produces bare rock with no soil, so ecosystem development begins from scratch.