Lichens are life forms that live in a symbiotic relationship in the environment they are found in. They may grow on plants or rocks, and are considered pioneer organisms because they are often the first type of plant life to establish in the environment.
Lichens show a sensitivity to compounds that are emitted from factory smoke stacks, such as sulfur dioxide. Sulfur dioxide is a primary pollutant that will mix in the atmosphere with water vapor to form acid rain. The acid rain has a debilitating effect on both animal life and plant life, such as lichens.
One would reasonably expect to see a severe drop-off in lichen growth in environmental areas surrounding factories that emit waste pollutants such as sulfur dioxide. The further away from the industrial setting one goes, the less likely one would expect to encounter acid rain as precipitation. This would promote the existence of plant growth like lichens. In pastoral settings, far away from the belching smoke stacks of industry, lichen growth and participation in the environmental setting would be restored to its maximum effect.