Primary succession is the process of lichen, algae, fungi, and eventually plants establishing themselves on new ground without soil. This could be a lava flow, or an area uncovered by a retreating glacier. Secondary succession is the process of plants re-establishing in areas already covered by soil, for example after a fire.
Riverine succession sometimes is primary (on large deep barren sandbar deposits) or secondary (where sediment deposition is shallow or doesn't bury pre-existing vegetation.
Primary succession usually takes longer than secondary succession.
