| Lichens are used as air quality indicators, but in urban areas effects of traffic pollution, moisture and colonization sources have not been distinguished. Is the reduced lichen cover and richness within cities due mainly to traffic pollution as is typically assumed? We studied lichens on 420 trees at 84 sites across urban Ottawa, Canada. Mixed models and model averaged standardized regression coefficients were used to compare relative effects of traffic pollution, moisture and colonization sources on lichens. We found that lichen cover is a good indicator of urban traffic pollution within 300m of a site, robust to influences of moisture and colonization sources. However, lichen species richness responded four times more strongly to moisture and colonization sources than to traffic pollution. Therefore, lichen cover can be used in monitoring urban traffic pollution, but not lichen species richness. For the purposes of conservation, increasing colonization sources through increased treed area is more important than controlling traffic pollution. |
