Response of four common lichen species to pollution, light, and nearby land cover: Predictions partially match 30-year patterns in upper midwestern USA

Background/Question/Methods

In a retrospective study we made predictions of response to pollution, light, and nearby land cover from 1979 morphological data for Flavoparmelia caperata (L.) Hale, Physcia millegrana Degel., Punctelia bolliana (Müll. Arg.) Krog, and Punctelia rudecta (Ach.) Krog in rural southern Wisconsin, USA. We have morphological data for these 4 species at 8 sites in 1979 from a 1974-1979 study of lichen response to emissions from a rural power plant. We made predictions for response to pollution, light and nearby land cover based on correlations and contingency tests of morphological data with environmental variables and improved pollution estimates developed in a 2003-2004 resurvey of study sites and then back-calibrated to 1979. We compared our predictions with 1974-2003 changes in distribution for these species at 24 sites surveyed in 1974, 1978, and 2003, and at 29 sites surveyed in 2003. We also compared the patterns of these 4 lichen species with those for groups of all species in the study with similar growth form.

Results/Conclusions

Greater 1979 morphological damage to F. caperata at sites with more air pollution from a point source was matched with lower abundance of that species at sites with more air pollution in 2003, after accounting for light response. 1979 predictions related to air pollution did not match later distribution changes for the other species. Three of the species had strong patterns of light response that were not matched with 1979 predictions. For all but Physcia millegrana, we found unexpected matches between 1979 predictions based on morphology and 1974-2003 distribution changes related to percent of forest cover near a site. In 1979 there were more damaged algal cells, increased bacteria on fungal hyphae, or unusual pruina on lobe tips at sites with less forest nearby. These 1979 anomalies were matched with long-term (1974-2003) declines or lower abundance in 2003 at sites with less forest nearby. Two possible mechanisms to explain responses to land cover pattern - agricultural air pollution and dispersal limitations - have little support from our data. Most small foliose lichen species increased over time while Physcia millegrana declined. The remaining species matched other large foliose lichen species in declining over time and becoming more restricted to sites with more forest nearby. All changes in lichen species can be linked to human impact on the landscape.