Q. What is the difference between primary ecological succession and secondary ecological succession?

The Primary ecological succession is the changing sequence of communities from the first biological occupation of a place where previously there were no living beings. For instance, the colonization and the following succession of communities on a bare rock.

The Secondary ecological succession is the changing sequence of communities from the substitution of a community by a new one in a given place. For instance, the ecological succession of the invasion of plants and animals in an abandoned crop or land.