In Thailand, some lichen studies had been conducted. Subsri (2001) used lichens as bioindicators for air pollution monitoring in urban and suburban in Chiang Mai city. It was found that high polluted areas were extended to suburban more than in 1996. This indicates that the air pollution had been increasing. It was, corresponded with the study of Muangsuwun (2006) who monitored the growth rate of the lichen Pyxine cocoes Swartz on the mango tree (Mangifera indica L.) in Chiang Mai City. It was found growth rate of P. cocoes in Chiang Mai city was slower than in Chiang Mai University because the air pollution in city is higher than Chiang Mai University, and less lichen species was found in the urban area while more lichens were found in Chiang Mai University.