Community analyses of epiphytic lichens were used to study the controlling factors of lichen abundance and diversity in urban and rural environments of Pittsburgh in southwestern Pennsylvania. Two urban sites included Schenley and Frick Parks in metropolitan Pittsburgh and two rural sites at Mingo Creek County Park in Washington County and Roaring Runs Natural Area in Westmoreland County. Community composition of lichens was measured at six intensive monitoring plots per site and site-wide species diversity surveys. The lichen diversity value, a statistical estimator of the environmental conditions at a site, was greater at the rural sites (20.8 ± 3.0) compared to the urban sites (11.3 ± 3.5) (± standard error), suggesting a less disturbed lichen community at Mingo and Roaring Runs. In the intensive monitoring plots, species richness was greater at Mingo and Roaring Runs compared to Schenley and Frick, averaging 5.2 ± 0.3, 4.7 ± 0.4, 3.7 ± 0.8 and 2.0 ± 0.4, respectively. The dominant lichens across all sites were Lepraria lobificans, an unidentified sterile crustose lichen and Cladonia ochrochlora. The dominance of nitrophilous and sulfur dioxide–tolerant lichens at all sites suggests that the lichen community within the larger geographical region is influenced by nitrogen and sulfur dioxide air pollutants. The differences between sampling sites are most likely driven by lichens responding to changes in urbanization, which include humidity and habitat fragmentation.

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