Answer: Lichens and mosses grow slowly on newly formed land, followed by grasses, shrubs, and trees.
An ecological succession describes series of changes that occur in a biotic community of the ecosystem with respect to changes in non-living components occurring in an ecosystem with due course of time until the ecosystem attains stability. A primary succession is a succession that occurs in a previous barren land where no life ever existed. For example area undergone with volcanic activity and retreating glacier. Lichens and mosses grow slowly on newly formed land, followed by grasses, shrubs and trees this is the example of primary succession taking place in an ecosystem. Lichens and mosses are pioneer species which means that they grow on the land which is not previously inhabited by any other plant species and facilitates and initiates the growth of new plant species. Lichens on bare rocks releases acids which decreases the compaction of the rocks. This helps in withering of rocks into small particles of soil. The soil particles aggregate to form soil which will be efficient for the growth of mosses. With the growth of mosses soil quality improves with time and this facilitates the growth of grasses, shrubs and trees.