Lichens on Tananei Olive trees

I still remember with pleasure the first time I saw lichens (plant organisms resulting from the symbiosis between a fungus and an algaes) on the olive trees at Tananei: I was worried because I didn't know how to remove them since they were everywhere and I feared they could be a problem for our beloved olive trees. Then we discovered with great pleasure that the presence of lichens, in addition to not creating any problems for the plants, is a clear sign that the air quality is very good, given that they live in environments where there is no pollution.