Primary succession begins in barren areas, such as on bare rock exposed
by a retreating glacier. The first inhabitants are lichens or
plants—those that can survive in such an environment. Over hundreds of
years these “pioneer species” convert the rock into soil that can
support simple plants such as grasses. These grasses further modify the
soil, which is then colonized by other types of plants. Each successive
stage modifies the habitat by altering the amount of shade and the
composition of the soil. The final stage of succession is a climax
community, which is a very stable stage that can endure for hundreds of
years.
The ecological succession that occurs on a preexisting soil after the primary succession has been disrupted or destroyed due to a disturbance that reduced the population of the initial inhabitants.