> just like the lichens on trees are an indicator of air pollution (few lichens mean a bad air quality). Lichen indicators for air pollution are fascinatingly

> just like the lichens on trees are an indicator of air pollution (few lichens mean a bad air quality). Lichen indicators for air pollution are fascinatingly more complicated than that. Certain lichens respond positively to air pollution due to excess nutrients like ammonia and nitrates in the air. Imagine an algal bloom but the nutrient pollution is in the air instead of in the water. The US Forest Service produced an interesting video overviewing these phenomena. Air Pollution & Lichens: A Tour of the Columbia River Gorge: https://www.youtube.com/watch?v=P3dPrgAkN3M https://www.youtube.com/watch?v=P3dPrgAkN3M