Diversity and sensitivity of epiphytes to oxides of nitrogen in London

This study investigated the distribution and diversity of epiphytes in London in relation to NOx using fine-scale atmospheric dispersion modelling. The survey recorded over 3000 epiphytes from 334 trees (Fraxinus excelsior) representing 74 lichen, 14 moss, 7 fungal and 3 algal species. There was a significant inverse relationship between diversity and NOx. Diversity declined where NOx exceeded 70 μg m−3 and NO2 exceeded 40 μg m−3, suggesting a phytotoxic effect. However, there was a significant positive relationship between NOx and lichen abundance due to the ubiquitous distribution of pollution tolerant species, mainly associated with eutrophication. A scale of lichen sensitivity to NOx has been derived.