Figure 3From: Long-term monitoring of environmental change in German towns through the use of lichens as biological indicators: comparison between the surveys of 1970, 1980, 1985, 1995, 2005 and 2010 in Wetzlar and GiessenAssessing air quality by combining diversity values of both reference species and indicators of hypertrophication. Modified from VDI 3957 Part 13[1].Back to article page