Lichens are epiphytic and absorb their nutrients from the air. This means they collect pollutants like nitrogen, sulfur, and toxic metals which can be analyzed in a lab. Collecting lichen tissue to analyze its elemental profile helps make determinations about the air quality of remote and sensitive places and is part of some mandated monitoring efforts. There are many wilderness areas that are too remote to use mechanical monitoring equipment. Lichen biomonitoring helps fill in these gaps.