Comparisons of epiphytes on oak trees between oceanic Devon sites and continental Norfolk localities. 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., Ammonia, Agriculture, British Isles, Nitrogen, Community Composition, Nitrophiles, Acidophiles, Nitrophytes, Epiphytes