Detecting changes in epiphytic lichen communities at sites affected by atmospheric ammonia from agricultural sources

Lichens were recorded on Quercus petraca trunks and twigs near ammonia recording stations in 'continental' Norfolk, and 'oceanic' Devon in order to test indicator values developed for epiphytic lichens in areas of high atmospheric ammonia in the Netherlands. Lichens on trunks in Norfolk showed a similar correlation of nitrophyte indices with ammonia concentration and bark pH as those in Holland, whereas in Devon there was no correlation with nitrophyte indices on trunks and a negative correlation with acidophyte indices. Results on twigs in both sites suggest that lichens on twigs respond more rapidly to recent changes in ammonia concentrations while trunks may maintain relict lichen communities due to either a legacy of previous acidification or ecological continuity. The results suggest that loss of acidophytes is taking place prior to the establishment of nitrophytes indicating the importance of establishing levels of ammonia at which sensitive communities are at risk.