What differentiates primary succession from secondary succession?

Primary succession is characterized by the development of an ecosystem in an area that has been lifeless, such as after a volcanic eruption, glacier retreat, or other events that leave bare rock or soil devoid of life. This process begins when pioneer species, such as lichens and mosses, colonize the barren environment, leading to soil formation and the gradual establishment of a more complex ecosystem.

In contrast, secondary succession occurs in areas where an existing ecosystem has been disturbed but soil and living organisms still remain, such as after a forest fire, flood, or human activities like farming. Since secondary succession starts with pre-existing soil and seeds, it tends to progress more quickly than primary succession.

The distinction in occurrences—where primary succession happens in completely lifeless areas—highlights the critical nature of the starting conditions in these ecological processes.