What role do lichens play in nature and human life?

Such seemingly small and nondescript organisms, like lichens, actually perform a number of functions that are most important for natural communities and humans. In nature, lichens:
1) are pioneers of lifeless land areas (primary succession)
2) producer – this means animal feed (in particular, reindeer feed on lichen)
3) enrich the soil with minerals
A person uses as:
1) an indicator of acidity in chemistry
2) air pollution indicator
3) a source of biologically active substances, including drugs
4) cosmetic product