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    Southern California's South Coast Air Basin includes the heavily urbanized Los Angeles and Orange counties, the inland urban and suburban areas, and the surrounding mountain ranges. Historically high air pollution makes the region a natural laboratory for investigating human impacts on natural systems. Regional lichen distribution records from the early 1900s compared to more extensive montane data collected in the 1970s demonstrated declining species distribution ranges, attributed to increasingly heavy air pollution conditions. In 2008, we surveyed 21 sites in the mountains surrounding the basin for lichens, 18 of which were surveyed in 1976-77, and we quantitatively compared communities across the thirty-year span. The 1976-77 findings showed a marked decrease in species distribution in comparison to anecdotal evidence from early 1900s collections and a 1913 flora. Our findings show that additional community shifts occurred since the earlier surveys, suggesting a worsening of pollution impact. Of the species in the region, Melanohalea subolivacea, one of the most pollution-sensitive species remaining in the Basin's flora, decreased markedly in abundance between 1976-77 and 2008. Lichens in the more nitrophilous genera Physcia, Physconia, and Xanthomendoza increased in abundance. No sensitive species have re-appeared since the '76-77' inventories.

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    Riddell, Jennifer; Jovan, Sarah; Padgett, Pamela E.; Sweat, Ken. 2011. Tracking lichen community composition changes due to declining air quality over the last century: the Nash legacy in Southern California. Bibliotheca Lichenologica. 106: 263-277.


    air pollution, lichen community composition, nitrogen, ozone, Southern California

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