What indicators can be made out of lichen?

Use as Bio-indicators. Lichens are ... A few lichen species can tolerate quite high levels of pollution and are commonly found on pavements, walls and tree bark in urban areas. ... Acid rain became a recognised international problem during the 1980s resulting from the dispersion of air pollutants via tall chimney stacks. read more

Bioindicators are living organisms that respond in an especially clear way to a change in the environment. The hardy lichens are useful bioindicators for air pollution, espeially sulfur dioxide pollution, since they derive their water and essential nutrients mainly from the atmosphere rather than from the soil. read more