Lichens and Mosses (a) and (b). Lichens and mosses release substances which break down the stones resulting in the formation of soil.

The fungal component of lichens produces organic acids that disintegrate rock, giving the lichen a better hold and contributing to the weathering process, which eventually turns a rock into soil.

As lichens die, they provide some organic matter that also contributes to soil. Mosses can then colonize the thin soil; as mosses die, the soil thickens more allowing other hardy species to colonize.