Answer: C. Forest fire
Step-by-step explanation:
An ecological disturbance is an event that is caused by a biological or non-biological agent. The agent is capable of negatively affecting the ecosystem. A primary ecological disturbance will be the one which will directly affect the ecosystem. For example flood, volcanic eruption, earthquake. A secondary ecological disturbance will be the one which will indirectly affect the ecosystem. For example volcanic eruption could be responsible for acid rain in the neighboring region.
The forest fire is the example of secondary disturbance because of the fact that initially the forest will affect a small region or small number of tree species but may spread to the large region. This will indirectly affect the animal species in a region. As, they may migrate, extinct or decrease in number.