Growth of Lichens on barren rocks is followed by the growth of :

In an ecological succession I.e. the process by which a barren ecosystem is converted into a living ecosystem, lichens are the pioneers for xerophytic succession. This is because the nutritional requirement of lichens is very less, so they bind too the rocks and release some acids that helps in the weathering of rocks and soil formation. Now on this soil, mosses are the first to grow since they feed on the dead lichens. Mosses are very tiny autotrophs and can easily grow on this soil.