Summary Lichens have been used to efficiently track major drivers of global change from the local to regional scale since the beginning of the industrial revolution (sulphur dioxide) to the present (nitrogen deposition and climate change). Currently, the challenge is to universalize monitoring methodologies to compare global change drivers’ simultaneous and independent effects on ecosystems and to assess the efficacy of mitigation measures. Because two protocols are now used at a continental scale North America (US) and Europe (EU), it is timely to investigate the compatibility of the interpretation of their outcomes. For the first time, we present an analytical framework to compare the interpretation of data sets coming from these methods utilizing broadly accepted biodiversity metrics, featuring a paired data set from the US Pacific Northwest. The methodologies yielded highly similar interpretation trends between response metrics: taxonomic diversity, functional diversity and community composition shifts in response to two major drivers of global change (nitrogen deposition and climate). A framework was designed to incorporate surrogates of species richness (the most commonly used empirical trend in taxonomic diversity), shifts in species composition (compositional turnover) and metrics of functional diversity (link between community shifts to effects and ecosystem structure and functioning). These metrics are essential to more thoroughly comprehend biodiversity response to global change. Its inclusion in this framework enables future cross‐continental analysis of lichen biodiversity change from North America and Europe in response to global change. Future works should focus on developing independent metrics for response to global change drivers, namely climate and pollution, taking us one step closer to a lichen‐based global ecological indicator.

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Evaluating the conservation value of ecological communities is critical for forest management but can be challenging because it is difficult to survey all taxonomic groups of conservation concern. Lichens have long been used as indicators of late successional habitats with particularly high conservation value because lichens are ubiquitous, sensitive to fine-scale environmental variation, and some species require old substrates. However, the efficacy of such lichen indicator systems has rarely been tested beyond narrow geographic areas, and their reliability has not been established with well-replicated quantitative research. Here, we develop a continuous lichen conservation index representing epiphytic macrolichen species affinities for late successional forests in the Pacific Northwest, USA. This index classifies species based on expert field experience and is similar to the “coefficient of conservatism” that is widely used for evaluating vascular plant communities in the central and eastern USA. We then use a large forest survey dataset to test whether the community-level lichen conservation index is related to forest stand age. We find that the lichen conservation index has a positive, linear relationship with forest stand age. In contrast, lichen species richness has only a weak, unimodal relationship with forest stand age, and a binary indicator approach (where species are assigned as either old growth forest indicators or not) has a substantially weaker relationship with forest stand age than the continuous lichen conservation index. Our findings highlight that lichen communities can be useful indicators of late successional habitats of conservation concern, and that indicator systems based on expert experience can have strong biological relevance.