Epiphytic lichens are sensitive to deteriorating air quality, but levels of nitrogen and especially sulphur deposition have been in decline over most of Europe in recent decades. We assessed the response of epiphytic lichens to this decline, using data from long-term monitoring sites in Sweden. We analyzed 20 years of data to investigate temporal trends in lichen communities’ sensitivity to sulphur, nitrogen preference, species richness and alpha and beta diversity. We found only limited and partial evidence of recovery in the area that previously had high levels of deposition, and a decline in mean sulphur sensitivity at a northern site with low deposition levels throughout the monitoring period. The slow recolonization of sensitive species, even where environmental conditions are now suitable, is probably a result of impoverished regional species pools and the inherent limited dispersal capacity of many lichen species. We suggest due consideration of these factors in the use of epiphytic lichens as environmental indicators in a period of improving air quality.

中文翻译：

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20 年来空气污染迅速下降，瑞典附生地衣群落恢复乏力

附生地衣对空气质量恶化很敏感，但近几十年来，欧洲大部分地区的氮，尤其是硫沉积水平一直在下降。我们使用瑞典长期监测站点的数据评估了附生地衣对这种下降的反应。我们分析了 20 年的数据，以调查地衣群落对硫、氮偏好、物种丰富度以及 α 和 β 多样性的敏感性的时间趋势。我们只发现了有限和部分的证据表明该地区以前沉积水平很高，并且在整个监测期间沉积水平较低的北部地点的平均硫敏感性下降。敏感物种的缓慢重新定殖，即使现在环境条件适宜，可能是区域物种库贫乏和许多地衣物种固有的有限传播能力的结果。我们建议在空气质量改善时期使用附生地衣作为环境指标时适当考虑这些因素。