To solve this problem, we need to understand the relationship between lichens and environmental conditions.$\newline$Lichens are symbiotic associations between fungi and algae or cyanobacteria. They are known to be bioindicators of air quality.$\newline \bullet$Lichens are sensitive to air pollution, especially sulfur dioxide and other pollutants.$\newline \bullet$In areas with high levels of pollution, lichens are often absent or show reduced growth.$\newline \bullet$Conversely, a location with luxuriant growth of lichens indicates that the air is clean and not polluted.$\newline$Therefore, the presence of luxuriant lichens on trees suggests that the location is not polluted.$\newline$This corresponds to Option 4: Location is not polluted.$\newline$Thus, the correct option is Option 4.