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A national citizen survey quantified the abundance of epiphytic lichens that are known to be either sensitive or tolerant to nitrogen (N) deposition. Records were collected across the UK from over 10,000 individual trees of 22 deciduous species. Mean abundance of tolerant and sensitive lichens was related to mean N deposition rates and climatic variables at a 5 km scale, and the response of lichens was compared on the three most common trees (Quercus, Fraxinus and Acer) and by assigning all 22 tree species to three bark pH groups. The abundance of N-sensitive lichens on trunks decreased with increasing total N deposition, while that of N-tolerant lichens increased. The abundance of N-sensitive lichens on trunks was reduced close to a busy road, while the abundance of N-tolerant lichens increased. The abundance of N-tolerant lichen species on trunks was lower on Quercus and other low bark pH species, but the abundance of N-sensitive lichens was similar on different tree species. Lichen abundance relationships with total N deposition did not differ between tree species or bark pH groups. The response of N-sensitive lichens to reduced nitrogen was greater than to oxidised N, and the response of N-tolerant lichens was greater to oxidised N than to reduced N. There were differences in the response of N-sensitive and N-tolerant lichens to rainfall, humidity and temperature. Relationships with N deposition and climatic variables were similar for lichen presence on twigs as for lichen abundance on trunks, but N-sensitive lichens increased, rather than decreased, on twigs of Quercus/low bark pH species. The results demonstrate the unique power of citizen science to detect and quantify the air pollution impacts over a wide geographical range, and specifically to contribute to understanding of lichen responses to different chemical forms of N deposition, local pollution sources and bark chemistry.

The relationship between different features of lichen communities in Quercus robur canopies and environmental variables, including concentrations of NO 2 and NH 3 was investigated. NO 2 concentration was the most significant variable, it was positively correlated with the proportion of lichen cover comprising nitrophytes and negatively correlated with total lichen cover. None of the lichen community features were correlated with NH 3 concentrations, which were relatively low across the site. Since nitrophytes and nitrophobes are likely to react in opposite directions to nitrogenous compounds, total lichen cover is not a suitable indicator for these pollutants. It is, therefore, suggested that the proportion of lichen cover comprising nitrophytes may be a suitable simple indicator of air quality, particularly in locations where the pollution climate is dominated by oxides of nitrogen.

Epiphytic lichens were sampled on mango trees (Mangifera spp.) in 32 sites in urban centres and surrounding rural areas in seven provinces of upper northern Thailand. Species were recorded on each tree and frequency estimated in a grid of ten 100-cm2 units. Analysis of macrolichen data showed that lichen diversity was inversely correlated with human population, and that lichen diversity was lowest in the cities with the highest population. The distribution and frequencies of species belonging to families Physciaceae and Parmeliaceae contributed to the groups identified by cluster analysis that corresponded to gradients in rainfall and population density. Comparison with modelled pollution data and local pollution records showed greater correspondence of lichen data with the effects of PM10 than with anthropogenic sulphur.

The distribution of lichen species in upland regions of Aberdeenshire, Scotland, is investigated along a landuse gradient from natural forest to intensive agriculture. Quantitative data on lichen communities on saxicolous, epiphytic and terricolous substrata were collected from 16 hectares in one km2 in each landuse type. Multivariate analyses, NMDS and Cluster analysis were used to identify lichen communities associated with environmental factors including landuse, substratum type and age. The epiphytic community of native pinewoods was distinguished from all others by the highest species richness, the presence of indicators of ecological continuity and the absence of nitrophytes, while the epiphytic communities of farmland were distinguished by absence of acidophytes and a high contribution of nitrophytes. Plantations of conifers were distinguished by low species richness and an increase in tolerant species. Saxicolous communities were frequent on walls in all sites except native pinewood, where saxicolous substrata were rare. Intensively farmed sites were distinguished by an increase in percentage contribution of nitrophytes. The high acidophyte contribution in all sites suggests that crustose species of acid rocks may not respond rapidly to an increase in applied nitrogen. In landscapes where tree cover is sparse or non-existent combined assessment of habitat diversity and nitrophyte indicator species can be used to assess changes associated with agricultural intensification.

Epiphytic lichens were sampled on selected trees in 19 sites radiating from Chiang Mai city including the adjacent mountain Doi Suthep in Northern Thailand using the VDI method (Verein Deutscher Ingenieure) to obtain frequency of occurrence in 10 area units per sampled tree. Sites selected included highly polluted sites in urban and adjacent industrial areas of Chiang Mai city, disturbed rural sites and undisturbed forest on Doi Suthep mountain, with altitudes varying from 260–1450 m. Lichen diversity was highest in upland sites and lowest in urban and agricultural sites. Analysis of lichen taxa at generic and at macrolichen species level and environmental data using PRIMER showed that upland and lowland sites were distinguished in the first division at both levels and correlated with altitude and vegetation type. Analysis of all taxa at generic level showed no separation of lowland sites but at macrolichen species level a better separation was obtained, suggesting that lichen diversity alone cannot be used for biomonitoring of air pollution. The relationship of epiphytic lichens to climate and pollution data available for Chiang Mai city and Doi Suthep is discussed and results compared with data from other studies in SE Asia.

A survey of epiphytic species on annual increments of Quercus petraea twigs in a west Wales woodland has shown that distribution of lichen species and rates of succession are affected by a range of environmental conditions. Lichen communities were recorded for 1–15 years on randomly sampled twigs along marked woodland boundaries affected by a range of climatic and management conditions. Results show that there is a correlation between environmental condition and lichen communities of twigs, and that indicator species can be used to detect trends towards acidification or eutrophication.