Geomatics and Landscape Ecology Research Laboratory Wednesday, 21 October 2020 3:01 am  
Heather Coffey
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Heather Coffey


Lichen diversity is related to air quality at a regional scale, increasing with distance to city centres. Here we ask whether lichens respond to air quality at smaller scales across a city, in landscapes up to 1km around sites. We hypothesized that other processes – differences in humidity and colonization pressure – might obscure relationships between lichens and air quality at these scales. We sampled lichen cover and diversity at 84 sites across urban Ottawa, Canada. We tested the independent effects of air pollution, humidity, and colonization pressure at multiple scales. We predicted lichens would respond negatively to traffic levels, as the principal source of air pollution within the city. We predicted lichens would respond positively to humidity, measured directly in the focal patch. Finally, we predicted lichens would respond positively to vegetative colonization pressure, measured as the treed (habitat) area around sites.

Lichens did not respond to traffic levels, suggesting that air pollution is not affecting Ottawa’s lichens at scales up to 1km around sites. Lichen diversity responded positively to humidity; the cover of individual species is either limited by, or independent of, humidity. Lichens did not respond to treed area, indicating that colonization pressure exerts a negligible influence on urban lichens. Additionally, the abundance of Candelaria concolour was a strong predictor of the diversity metric, making it an ideal indicator of lichen diversity values within the city. These results suggest that lichen relevées are not sufficiently precise to reveal urban air quality patterns due to traffic within urban Ottawa.

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