Lichens have been used to study air pollution chemistry in national parks and forests since the 1980s (Figures 1 and 2). There have also been a few lichen studies on national wildlife refuges. Most of the studies have been floristic studies, reports of baseline concentrations of elements in lichen tissues and, occasionally, trends in these concentrations. Figure 1 shows park and refuge locations with tissue chemistry data. USGS Biological Resources Division maintains a web site listing lichens known from each of the national parks shown on the map (). Results from these studies.
