Figure 4From: 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 Giessen pH changes in bark of Tilia spp ., Populus spp. and Malus domestica in Wetzlar and Giessen. Back to article page