Question

Why are lichens a good indicator of the environment's health?

Answer 1

Lichens, along with other sensitive species such as salmon, are good indicators of environmental health as they are sensitive to their environments.

Explanation:

The conditions, acidity, humidity, and ecosystem impact the life of these species and small shifts in these factors can heavily impact the population.
Refer to the Wikipedia article for more:
https://en.wikipedia.org/wiki/Indicator_species